Nalcor Energy
Three Dimensional (3D) Hydrogeological
Study for the North Spur
Final Report
H346252-0000-00-124-0001
Rev. 0
October 23, 2015
This document contains confidential information intended only for the person(s) to whom it is addressed. The information
in this document may not be disclosed to, or used by, any other person without Hatch's prior written consent.
Nalcor Energy
Three Dimensional (3D) Hydrogeological
Study for the North Spur
Final Report
H346252-0000-00-124-0001
Rev. 0
October 23, 2015
This document contains confidential information intended only for the person(s) to whom it is addressed. The information
in this document may not be disclosed to, or used by, any other person without Hatch's prior written consent.
Nalcor Energy
Hydrogeological Model of North Spur
H346252
Disclaimer
This report has been prepared by Hatch Ltd. (Hatch) for the sole and exclusive use of Nalcor
Energy (the “Client”) for the purpose of assisting the management of the Client in making
decisions with respect to the Muskrat Falls Hydroelectric Project and shall not be (a) used for
any other purpose, or (b) relied upon by any third party.
Hatch acknowledges that this report may be provided to third parties in connection with the
development, construction and operation of the Muskrat Falls Hydroelectric Project; provided
that all such parties shall rely upon these deliverables at their own risk and shall (by virtue of
their acceptance of the report) be deemed to have (a) acknowledged that Hatch shall not
have any liability to any party other than the Client in respect of the deliverables and (b)
waived and released Hatch from any liability in connection with the deliverables.
This report contains opinions, conclusions and recommendations made by Hatch, using its
professional judgment and reasonable care. Any use of or reliance upon this report by the
Client is subject to the following conditions:
a) The report being read in the context of and subject to the terms of the Engineering
Services Agreement between Hatch and the Client (the “Agreement”), including any
methodologies, procedures, techniques, assumptions and other relevant terms or
conditions that were specified or agreed therein;
b) The report being read as a whole, with sections or parts hereof read or relied upon in
context;
c) The conditions of the study area at North Spur of the Muskrat Falls Project may change
over time or may have already changed due to natural forces or human intervention, and
Hatch takes no responsibility for the impact that such changes may have on the accuracy
or validity or the observations, conclusions and recommendations set out in this report;
and
d) The report is based on information made available to Hatch by the Client; and unless
stated otherwise in the Agreement, Hatch has not verified the accuracy, completeness or
validity of such information, makes no representation regarding its accuracy and hereby
disclaims any liability in connection therewith.
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Table of Contents
Executive Summary .................................................................................................................................. vii
1. Introduction ........................................................................................................................................... 1
1.1
Study Objectives ........................................................................................................................... 1
2. Reference Documentation ................................................................................................................... 3
3. Hydrogeological Overview .................................................................................................................. 5
3.1
3.2
3.3
Stratigraphy................................................................................................................................... 5
3.1.1 Upper Sand ...................................................................................................................... 5
3.1.2 Stratified Drift ................................................................................................................... 5
3.1.3 Lower Marine Clay ........................................................................................................... 5
3.1.4 Lower Aquifer Layer......................................................................................................... 5
3.1.5 Bedrock ............................................................................................................................ 6
Hydrogeological Conditions .......................................................................................................... 6
3.2.1 Perched Water Level in the Upper Sand Layer ............................................................... 6
3.2.2 Upper Drift / Intermediate Aquifer Deposits (IA) .............................................................. 6
3.2.3 Lower Aquifer (LA) ........................................................................................................... 6
Existing Stabilization Measures and Pumping Tests .................................................................... 7
3.3.1 Upper Drift / Intermediate Aquifer Deposits ..................................................................... 7
3.3.2 Lower Aquifer................................................................................................................... 7
4. Design Stabilization Measures ............................................................................................................ 9
5. Modeling Methodology ...................................................................................................................... 10
5.1
5.2
5.3
5.4
5.5
Introduction ................................................................................................................................. 10
Model Layers and Extents .......................................................................................................... 10
Meshing ...................................................................................................................................... 11
Lower Aquifer Model ................................................................................................................... 11
5.4.1 General .......................................................................................................................... 11
5.4.2 Material Properties......................................................................................................... 11
5.4.3 Boundary Conditions ..................................................................................................... 12
Upper Drift/Intermediate Aquifer Deposits (IA) Model ................................................................ 13
5.5.1 General .......................................................................................................................... 13
5.5.2 Modifications to the Geologic Model.............................................................................. 13
5.5.3 Material Properties......................................................................................................... 14
5.5.4 Boundary Conditions ..................................................................................................... 14
5.5.5 Modeling Approach - Stabilization Measures, Pumping, and Pressure Relief
Wells .............................................................................................................................. 15
6. Calibration Results ............................................................................................................................. 17
6.1
6.2
Lower Aquifer .............................................................................................................................. 17
6.1.1 Existing Conditions (Case C-1) ..................................................................................... 17
6.1.2 Lower Aquifer Pump Test (Case C-2) ........................................................................... 18
6.1.3 Validation Case (Case C-3) ........................................................................................... 19
Upper Drift and Intermediate Aquifer (IA) ................................................................................... 20
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6.3
6.2.1 Existing Conditions (Case C-4) ..................................................................................... 20
6.2.2 Short-term Pump Test (C-5) .......................................................................................... 21
6.2.3 Long-term Pump Test (C-6)........................................................................................... 22
Summary..................................................................................................................................... 23
7. Model Predictions ............................................................................................................................... 25
7.1
7.2
Lower Aquifer (LA) ...................................................................................................................... 25
7.1.1 General .......................................................................................................................... 25
7.1.2 Do Nothing Case ........................................................................................................... 26
7.1.3 Pressure Relief in the Lower Aquifer ............................................................................. 26
Upper Drift/Intermediate Aquifer Deposits (IA) ........................................................................... 28
7.2.1 Cases Analyzed ............................................................................................................. 28
7.2.2 Stabilization Measures................................................................................................... 28
7.2.3 Results for Reservoir Impoundment without Stabilization Works (Do Nothing) ............ 29
7.2.4 Reservoir at El. 17.5m – with Pump Well System ......................................................... 30
7.2.5 Reservoir at El. 17.5m – with Finger Drains and Pump Well System ........................... 30
7.2.6 Reservoir at El. 25m – Impact of Cut-off Wall, Till Blanket, Finger Drains and
Pump Well System ........................................................................................................ 33
7.2.7 Reservoir at El. 39m – Impact of Cut-off Wall, Till Blanket, Finger Drains and
Pump Well System ........................................................................................................ 35
7.2.8 Impact of Penetration Depth in Lower Clay for Cut-off Wall .......................................... 35
7.2.9 Impact of Reservoir Impoundment on Kettle Lakes ...................................................... 38
8. Summary ............................................................................................................................................. 41
8.1
8.2
8.3
Lower Aquifer .............................................................................................................................. 41
Upper Drift / Intermediate Aquifer Deposits ................................................................................ 42
Future Considerations ................................................................................................................ 45
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List of Tables
Table 3-1: Summary of Short Term Pumping Tests in Intermediate Aquifer (1981) .................................... 7
Table 3-2: Summary of Long Term Pumping Tests in Intermediate Aquifer (1981-1983) ............................ 7
Table 5-1: Hydraulic Conductivity Values Used in Lower Aquifer 3D FEFLOW Model .............................. 12
Table 5-2: Summary of the Boundary Conditions for Lower Aquifer 3D FEFLOW Model .......................... 12
Table 5-3: Hydraulic Conductivities Used in FEFLOW Model for Intermediate Aquifer ............................. 14
Table 5-4: Summary of the Boundary Conditions of 3D FEFLOW Model for Intermediate Aquifer ........... 15
Table 6-1: Summary of the Conditions for Lower Aquifer Model Calibration .............................................. 17
Table 6-2: LA Calibration Results for the Existing Conditions .................................................................... 18
Table 6-3: Summary of the Results for Pumping Test in 1979 from Lower Aquifer 3D FEFLOW Model ... 19
Table 6-4: Summary of the Results for Piezometric Response Due to River Level Increase in 1979 from
Lower Aquifer 3D FEFLOW Model ............................................................................................................. 19
Table 6-5: Summary of the Conditions for Intermediate Aquifer Model Calibration ................................... 20
Table 6-6: Calculated and Measured Initial Conditions in the IA ................................................................ 21
Table 6-7: Summary of the Results for Short-term Pumping Test Based on FEFLOW Modeling.............. 22
Table 6-8: Summary of the Results for Long-term Pumping Tests Based on FEFLOW Modeling ............ 23
Table 7-1: Summary of the Case Studies for 3D FEFLOW Modeling of Lower Aquifer ............................. 25
1
Table 7-2: Summary of the Updated UTM Coordinates of Relief Wells in 3D FEFLOW Model ................ 25
Table 7-3: Calculated Piezometric Head in Lower Aquifer – No Relief Wells ............................................ 26
Table 7-4: Calculated Head in the Lower Aquifer – With Installation of 10 Relief Wells ............................ 27
Table 7-5: Calculated Head in Lower Aquifer at the Relief Wells ............................................................... 28
Table 7-6: Summary of Case Studies of Intermediate Aquifer Model ........................................................ 29
Table 7-7: Calculated Piezometric Heads in the IA – Without Stabilization Measures............................... 30
Table 7-8: Calculated Piezometric Heads at the U/S WL of El.17.5m with Finger Drains and the Existing
Dewatering System ..................................................................................................................................... 32
Table 7-9: Summary of Calculated Piezometric Response at U/S WL=El. 25m with Installation of
Stabilization Elements and Operation of Pump Wells ................................................................................ 34
Table 7-10: Summary of Calculated Piezometric Response at U/S WL = El.39 m with Installation of
Stabilization Elements and Operation of Pump Wells ................................................................................ 37
Table 7-11: Summary of Calculated Response for Kettle Lakes at U/S WL = El.25 m .............................. 40
Table 7-12: Summary of Calculated Response for Kettle Lakes at U/S WL = El.39 m .............................. 40
Table 8-1: Summary with Reservoir at El. 17.5m ...................................................................................... 45
Table 8-2: Summary with Reservoir at El. 25m ......................................................................................... 45
Table 8-3: Summary with Reservoir at El. 39 m ........................................................................................ 45
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List of Figures
Figure 1-1:
Site Location
Figure 1-2:
Aerial Photograph of the Site (Google Earth, 2014)
Figure 1-3:
Ground Topography and River Bathymetry Based on LiDAR Imagery
Figure 3-1:
Hydraulic Conductivity versus Depth in Bedrock Based on Packer Testing in 1979
Figure 3-2:
Layout of the Dewatering Pumpwells Installed in 1981
Figure 3-3:
Location of Lower Aquifer Wells and Piezometers
Figure 5-1:
3D DXF Geological Model (Converted from Catia Data)
Figure 5-2:
Cross Section through Catia Model
Figure 5-3:
3D Finite Element Mesh – Lower Aquifer
Figure 5-4:
3D Finite Element Mesh – Upper Drift Deposits (IA)
Figure 5-5:
Boundary Conditions of 3D FEFLOW Model for LA
Figure 5-6:
Boundary Conditions of 3D FEFLOW Model for LA-Cont’d
Figure 5-7:
Boundary Conditions of 3D FEFLOW Model for LA-Cont’d
Figure 5-8:
Function of the Flux into LA versus Reservoir Heads Based on 2D FE Seepage Analyses
Figure 5-9:
An Impervious Layer Covering the D/S Scarps Slope Surface in 3D FEFLOW Model of IA
Figure 5-10: Boundary Conditions for IA 3D FEFLOW Model
Figure 5-11: Boundary Conditions for IA 3D FEFLOW Model-Cont’d
Figure 5-12: Relationship between the N-W flux and Upstream Reservoir Levels for IA
(Developed from 2D FE Seepage Analyses)
Figure 6-1:
Hydraulic Head Contours in the LA - Initial Conditions (@U/S WL=El.17.5 m)
Figure 6-2:
Hydraulic Head Contours in the LA during Pumping Test
Figure 6-3:
Pump Well F2 Installed in the LA 3D Model
Figure 6-4:
Piezometric Contours for the Upper Drift Deposits - Initial Conditions
Figure 6-5:
Hydraulic Head Contours for Short Term Pumping Test from FEFLOW Modeling
Figure 6-6:
Hydraulic Head Contours after 13 Months Pumping Test from FEFLOW Modeling
Figure 6-7:
Hydraulic Head Contours after 27 Months Pumping Test from FEFLOW Modeling
Figure 7-1:
Pressure Relief Wells A to J in the 3D FEFLOW Model of LA
Figure 7-2:
Hydraulic Head Contours of LA at @ U/S WL=El.25 m
Figure 7-3:
Hydraulic Head Contours of LA at @ U/S WL=El.39 m
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Figure 7-4:
U/S Cut-off Wall and Till Blanket in the 3D FEFLOW Model
Figure 7-5:
D/S Finger Drains in 3D FEFLOW Model
Figure 7-6:
Hydraulic Head Contours of IA at U/S WL=El.25 m before Stabilization (IA-1)
Figure 7-7:
Hydraulic Head Contours of IA at U/S WL=El.39 m before Stabilization (IA-6)
Figure 7-8:
Hydraulic Head Contours of IA at U/S WL=El.17.5m with Pump Well System (IA-0-b)
Figure 7-9:
Hydraulic Head Contours of IA at U/S WL=El.17.5m with D/S Finger Drain (IA-0-c)
Figure 7-10: Hydraulic Head Contours of IA at U/S WL=El.17.5m with D/S Finger Drain and Pumping
(IA-0-c)
Figure 7-11: Hydraulic Head Contours of IA at U/S WL=El.25 m before Stabilization (IA-1)
Figure 7-12: Hydraulic Head Contours of IA at U/S WL=El.25 m after Installation of COWs (IA-2)
Figure 7-13: Hydraulic Head Contours of IA at U/S WL= El.25 m after Installation of COWs + Blankets
(IA-3)
Figure 7-14: Hydraulic Head contours of IA at U/S WL= El. 25 m after Installation of COWs+ Blankets+
Finger Drains (IA-4)
Figure 7-15: Hydraulic Head Contours of IA at U/S WL=El. 25 m after Installation
of COWs+ Blankets+ Finger Drains+ Pump Wells System ( IA-5)
Figure 7-16: Calculated Hydraulic Head Profile in IA at U/S WL= El.25 m after Installation
of Stabilization Works
Figure 7-17: Hydraulic Head Contours of IA at U/S WL= El.39m before Stabilization (IA-6)
Figure 7-18: Hydraulic Head Contours of IA at U/S WL= El.39m after Installation of COWs (IA-7)
Figure 7-19: Hydraulic Head Contours of IA at U/S WL= El.39 m after Installation of COWs + Blankets
(IA-8)
Figure 7-20: Hydraulic Head Contours of IA at U/S WL= El.39 m after Installation of COWs+ Blankets+
Finger Drains (IA-9)
Figure 7-21: Hydraulic Head contours of IA at U/S WL= El.39m after Installation
of COWs+ Blankets+ Finger Drains+ Pump Wells System (IA-10)
Figure 7-22: Calculated Hydraulic Head Profile in IA at U/S WL= El.39m after Installation
of Stabilization Works
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List of Appendices
Appendix A
Modeling Basis for 3D Hydrogeological Study of the North Spur
Appendix B
2D Seepage Analysis for Estimation of Inflow Flux in Lower Aquifer and
Intermediate Aquifer of the North Spur
Appendix C
3D FEFLOW Sensitivity Analyses for Lower Aquifer of the North Spur
Appendix D
3D FEFLOW Sensitivity Analyses for Intermediate Aquifer of the North
Spur
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Executive Summary
This report describes the results of three dimensional (3D) hydrogeological modeling of the
North Spur, which is located at the Muskrat Falls hydroelectric site; part of the Lower
Churchill project (LCP) near Happy Valley/Goose Bay, Labrador (Newfoundland and
Labrador).
The North Spur comprises a body of stratified sediments up to 250 m in depth that forms a
partial closure of the Churchill River at the site of the Muskrat Falls hydroelectric project. A
series of landslides have occurred historically along both the upstream (U/S) and downstream
3
(D/S) shore lines of the North Spur. In November 1978, about 1.0 million m of soil materials
were engaged in a landslide on the downstream slope of the Spur. Figure ES-1 shows the
site and the latest LiDAR based ground topography and river bathymetry.
The stability of the North Spur during and after reservoir impoundment is a major concern of
the project. In order to reinforce the Spur, stabilization works have been designed including
an upstream (U/S) cut-off wall and till blanket, earthworks to reshape the geometry of the
Spur with berms, and downstream (D/S) drainage measures comprising filters, finger drains,
and pressure relief wells. The site has an existing dewatering system installed in 1981, which
has been operating as part of existing stabilization measures.
The objectives of this study were to:
•
model and investigate the initial North Spur groundwater seepage patterns;
•
assess the impact of the stabilizing measures on piezometric levels through the body of
the Spur at various reservoir levels;
•
provide model results to validate the stabilization works design;
•
provided model results that can be used to assess if the existing pumping system can be
discontinued after implementation of the stabilization works;
•
evaluate the effect of reservoir impoundment on the kettle lakes at the north end of the
Spur; and
•
provide a monitoring and forecasting tool of changes in the piezometric head within the
geologic units of the Spur during construction, impoundment and operation.
Model Basis and North Spur Stratigraphy
In this study, two 3D hydrogeological models were developed and analyzed using the
commercial finite element (FE) software FEFLOW Version 6.2. The hydrogeological models
are based on the North Spur interpreted geology as defined in the 3D Catia model developed
by SNC Lavalin Inc. (SLI Catia Model, 2013). The Catia Model is a 3D geologic model of the
site based on data from comprehensive site investigations dating back to the 1970’s and
including recent investigations performed in 2013 to support detailed design.
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Based on the Catia Model, the following soil deposits play a significant role in the
hydrogeologic setting at the site:
Lower Aquifer (LA) and Marine Clay
A lower aquifer (LA) overlies the bedrock at the site. The LA comprises a thick layer of sand
and gravel with boulders, which is overlain by an essentially continuous layer of marine clay.
Based on geologic and hydrogeological data, the marine clay acts as an aquiclude or
confining layer for the lower aquifer within the study area. There is a general lack of evidence
showing hydraulic connection between the lower aquifer (LA) and upper deposits at the site;
however, there is evidence of a local connection downstream of the rock knoll associated with
a scour hole in the Churchill River bed. The scour hole location is illustrated in Figure ES-1.
Upper Drift / Intermediate Aquifer Deposits (IA)
There is a complex sequence of drift deposits overlying the LA and marine clay deposits. The
drift deposits are highly heterogeneous but have the following general layered sequences
from top to bottom:

An upper sand layer

Upper silty clay layer

Upper silty sand (Drift - Zone A)

Lower silty clay layer, and

Lower silty sand (Drift - Zone B)

The silty sand layers are semi-pervious deposits and are referred to as the intermediate
aquifer (IA) in past documentation. The North Spur is formed by these deposits.
Slide Debris
Low permeable slide debris appears to have accumulated in the various landslide scarps
illustrated in Figure ES-1. Seepage models indicate that the debris impedes groundwater
drainage from the Spur toward the east or D/S side. The low permeable slide debris should
be verified by a site investigation program prior to implementation.
3-Dimensional (3D) Seepage Modeling
Separate 3D FEFLOW models were developed for the LA and IA, respectively, to assess
their response during reservoir impoundment. This was considered acceptable given the low
permeable marine clay layer between the upper IA and LA deposits and the paucity of data
showing a connection between the IA and LA. The model extents are illustrated by the
dashed line in Figure ES-1.
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Finite Element (FE) Mesh sensitivity studies were conducted to ensure adequate mesh
refinement and accuracy as described in the main body of this report. Then the models were
calibrated using the following data:
•
Historic piezometric data prior to 1981 (i.e. before installation of dewatering wells);
•
Short-term pumping tests in the lower aquifer deposits;
•
Historic piezometric responses in lower aquifer to the short-term flooding event in the
early 1980s; and
•
Short and long-term pumping tests in the upper drift deposits (intermediate aquifers) after
installation of dewatering wells in 1981.
Scour Hole
Figure ES-1: Ground Topography and River Bathymetry Based on LiDAR Imagery
The main variables during the calibration were the hydraulic conductivities of the subsurface
units, surface infiltration and subsurface inflows to the model area from the regional
groundwater regimes situated north and west of the site. In order to calibrate the models, the
measured hydraulic conductivities for the subsurface units were used ’as is’ with little or no
alteration; the surface infiltration and subsurface inflows (fluxes) were adjusted until good
agreement was obtained between measured and calculated piezometric levels.
st
The U/S reservoir will be raised in two stages to water levels of El. 25m (the 1 stage) and El.
nd
39 m (the 2 stage), respectively. The calibrated FE models were subsequently used to
estimate the response of the IA and LA deposits during reservoir impoundment and the FE
results were used to assess the effectiveness of:
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•
the U/S blanket and cutoff wall;
•
the D/S pressure relief well system;
•
the D/S finger drains; and
•
the existing pumped well system after implementation of the preceding design measures.
The following section summarizes the numerical results.
Modeling Results Summary
Lower Aquifer (LA)
•
There is significant regional groundwater flow entering the site or model domain from the
north and west directions (see the dashed lines in Fig. ES-1). These inflows have a
strong effect on the piezometric levels in the LA and they have been estimated as part of
the model calibration exercise. Based on the calibration exercise, it is estimated that
about 5 times more groundwater enters the North Spur site from the west (i.e. flowing
parallel to the river) compared to the north.
•
The groundwater inflow (flux) entering the model domain from the west increases
approximately linearly with increasing of the reservoir level. Using a 2D seepage model,
-2
3
2
-2
3
2
-2
approximate inflows (i.e. fluxes) of 3 × 10 m /m /day, 4.6 × 10 m /m /day and 7.5 × 10
3
2
m /m /day were estimated to enter the site from the west corresponding to U/S water
st
levels of El. 17.5m (existing condition), El. 25m (the 1 stage reservoir rising) and El. 39m
(the final reservoir rising), respectively.
•
Without installation of the proposed ten D/S pressure relief wells (i.e. Do Nothing case),
the FE model for the LA indicates that average piezometric heads will increase by about
2.2 m compared to the existing condition when the U/S water level is raised to El. 25m;
there will be about 5.2 m increase in piezometric head during the final rise to El. 39 m.
•
After installation of the D/S pressure relief wells, the FE results are identical to the Do
Nothing case indicating that pressure relief wells are expected to be ineffective for the
majority of the LA below the spur as described below in the next bullet point.
•
Piezometric levels (calculated) at the proposed pressure relief well locations in the LA will
rise from about El. 4.3 m corresponding to the existing conditions to El. 5.4 m and El. 6.9
m corresponding to U/S water levels of El. 25 m and El. 39 m, respectively. The
calculated piezometric levels are below the proposed outlet elevation at El. 7.0 m to El.
8.5 m corresponding to the ground surface. Provided the model assumptions are correct
and the lower aquifer is confined under a thick continuous layer of low permeability
marine clay, the relief wells should not be required for the lower aquifer. The pressure
relief wells will have no impact on piezometric levels in the North Spur after impoundment
unless a siphon system is employed or the outlet can be lowered below El. 4.0 m
(approximately).
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•
Significant deviations from the results summarized above for the LA may indicate either
leakage through the marine clay somewhere upstream of the hydroelectric development,
leakage into the lower aquifer through fractured rock at the Muskrat Falls site, or that the
marine clay layer has limited lateral and U/S continuity.
Upper Drift/Intermediate Aquifer Deposits (IA)
This section summarizes the calculated behavior of the upper drift deposits accounting for the
effect of the stabilizing measures. It is noted that the numerical results are dependent on the
model assumptions and these assumptions must be validated in the field during construction
and impoundment.
In the following sections, changes in the North Spur groundwater levels are reported relative
to the piezometric levels in the Spur before installation of the dewatering system in 1981 (i.e.
existing geometry, stratigraphy, and without the pump well system operating); This is
hereafter referred to as Existing Conditions. The impacts of operating the pumping well
system and implementing the proposed stabilization works on the hydraulic heads in the Spur
have been investigated. Relative increases in the piezometric levels correspond to a
reduction in the stability of the Spur slopes relative to the Existing Conditions case;
conversely, decreases in piezometric head indicate improvement.
Currently, there are high piezometric levels present in the southern block of the Spur, which is
the most critical part of the study area. The modeling indicates that the high levels cannot be
attributed to surface infiltration alone. Extensive analyses were performed to investigate
potential sources that could induce such high piezometric readings in the southern block of
the Spur. At the conclusion of the analyses, it was found that FEFLOW models for the IA
could only be calibrated against measured piezometric levels if a layer of low permeable
material (i.e. slide debris) was modeled on the D/S surface of the Spur in the old failure
scarps. This material within the slide zones is thought to consist of low permeable slide
debris from historical landslides; the debris has apparently blocked seepage outlets on the
D/S slope (i.e. adjacent to the rock knoll) leading to the high piezometric readings.
Existing Conditions
This section summarizes analyses results corresponding to an U/S water level of 17.5 m, and
D/S water level of 3 m.
•
Without installation of the existing pump well system, the piezometric heads in the upper
drift deposits are high with an average head of El. 29.6 m in the modeling area. The
average head in the southern block of the Spur is about El. 26.6 m
•
If the pump well system is operating, the piezometric levels in the Spur decrease by 5.3
m on average compared to existing conditions. The average head in the south block of
the Spur decreases by about 9.1 m.
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•
If the finger drains are installed and the existing pump well system is discontinued, the
piezometric levels in the Spur decrease by 3.5 m average compared to existing
conditions. The average head in the south block of the Spur decreases by about 5.9 m.
•
If the finger drains are installed and the pump well system is operated according to
existing pump rates, the piezometric heads are estimated to decrease by 8.9 m on
average compared to existing conditions. The average head in the south block of the
Spur decreases by about 15.9 m.
Accordingly, operation of the existing dewatering system caused a relatively larger drawdown
in the south block but less impact on the rest of the Spur; The D/S finger drains have a
significant impact on lowering the piezometric levels in the southern block of the Spur but the
impact is less than the dewatering system. Operating the pumped well system and installing
D/S finger drains have the biggest impact on piezometric levels in the south block, which is
considered as the most critical part of the North Spur.
Table ES-1 Summary with Reservoir at El. 17.5m
Location
Average All Piezometers
Average South Block only
Existing
Condition
El. 29.6 m
El. 26.6 m
With
Pumping
-5.3 m
-9.1 m
With Finger
Drains
-3.5 m
-5.9 m
Both
-8.9m
-15.9m
First Stage Reservoir Impoundment (El. 25 m)
This section summarizes analyses undertaken for the U/S water level of 25m and a D/S water
level of 3 m.
•
Without stabilization works and assuming the existing pump well system is discontinued
(i.e. Do Nothing), the piezometric levels in the Spur increase by 1.0 m in average
compared to existing conditions. The average head in the south block of the Spur
increases by about 1.3 m.
•
With the cut-off wall only and no till blanket, finger drains, or pumped wells, the
piezometric levels in the Spur decrease by 0.2 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 0.6 m.
•
With construction of the cut-off wall and till blanket but without finger drains and pumping,
the piezometric levels in the Spur increase by 1.4 m on average compared to existing
conditions. The average head in the south block of the Spur increases by about 1.9 m.
This occurs because the U/S blanket impedes drainage toward the U/S slope.
•
With construction of the cut-off wall, till blanket and finger drains implemented but no
pumping, the piezometric levels in the Spur decrease by 2.7 m on average compared to
existing conditions. The average head in the south block of the Spur decreases by about
4.6 m.
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•
With construction of the entire stabilization works and operation of the pump wells, the
piezometric levels in the Spur decrease by 8.0 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 14.6 m.
Table ES-2 Summary with Reservoir at El. 25m
Location
Average All Piezometers
Average South Block only
Do
Nothing
CoW
Only
CoW and
Blanket
+1.0 m
+1.3 m
-0.2 m
-0.6 m
+1.4 m
+1.9 m
CoW,
Blanket &
Drains
-2.7 m
-4.6 m
All
-8.0 m
-14.6 m
Final Stage Reservoir Impoundment (El. 39 m)
This section summarizes analyses undertaken for the U/S water level of 39 m and a D /S
water level of 3 m.
•
Without stabilization works and discontinuing the existing pump well system (i.e. Do
Nothing), the piezometric levels in the Spur increase by 6.7 m on average compared to
existing conditions. The average head in the south block of the Spur increases by about
9.8 m.
•
With the cut-off wall only and no till blanket, finger drains, or pumped wells, the
piezometric levels in the Spur increase by 3.2 m average compared to existing
conditions. The average head in the south block of the Spur increases by about 4.3 m.
•
With construction of the cut-off wall and till blanket but without finger drains and pumping,
the piezometric levels in the Spur increase by 6.6 m average compared to existing
conditions. The average head in the south block of the Spur increases by about 9.4 m.
This occurs because the U/S blanket impedes drainage toward the U/S slope.
•
With construction of the cut-off wall, till blanket and finger drains implemented but no
pumping, the piezometric levels in the Spur decrease by 1.5 m on average compared to
existing conditions. The average head in the south block of the Spur decreases by about
3.6 m.
•
With construction of the entire stabilization works and operation of the pump wells, the
piezometric levels in the Spur decrease by 7.7 m average compared to existing
conditions. The average head in the south block of the Spur decreases by about 15.3 m.
Table ES-3 Summary with Reservoir at El. 39 m
Location
Average All Piezometers
Average South Block only
Do
Nothing
CoW
Only
CoW and
Blanket
+6.7 m
+9.8 m
+3.2 m
+4.3 m
+6.6 m
+9.4 m
CoW,
Blanket &
Drains
-1.5 m
-3.6 m
All
-7.7 m
-15.3 m
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Impact of Penetration Depth in Lower Clay for Cut-off Wall
•
The results of sensitivity analyses indicated that the penetration depth of the cut-off wall
in the lower clay has a negligible impact on the piezometric heads in the intermediate
aquifer drift deposits.
Impact on the Kettle Lakes
•
The following lake levels are predicted corresponding to analysis performed assuming no
stabilization measures and with discontinuation of the pump well system
Table ES-4 Lake Levels without Stabilization Measures
Reservoir Elevation (m)
Upper Lake Water Elevation (m)
Lower Lake Water Elevation (m)
25.0
39.0
39.0
39.5
30.0
31.5
•
The following lake levels are predicted corresponding to analysis performed assuming
implementation of the cut-off wall, till blankets and finger drains and discontinuation of the
pump well system
Table ES-5 Lake Levels with Stabilization Measures
Reservoir Elevation (m)
Upper Lake Water Elevation (m)
Lower Lake Water Elevation (m)
25.0
39.0
37.4
38.7
28.5
29.2
•
Simulation of the pumping system operating according to the current pump rates had an
insignificant impact on the lake levels.
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1.
Introduction
Hatch Ltd. (Hatch) was retained by Nalcor Energy (Nalcor) to perform 3-Dimensional (3D)
seepage modeling of the North Spur at the site of the Muskrat Falls hydroelectric
development near Happy Valley Goose Bay, Labrador. The site location is shown in
Figure 1-1. This study commenced on January 27, 2014, when a Hatch geotechnical
engineer visited the LCP St. John’s project office to collect the data that was used for the
basis of the modeling program.
Figure 1-2 shows an aerial photograph of the site (Google Earth, 2014). Referring to
Figure 1-2, the Churchill River flows west to east through a narrowing of the river where the
Muskrat Falls Generating Station (GS) and dam will be built. When completed, the dam and a
landform referred to as the ‘North Spur’ will provide reservoir containment.
The North Spur (Spur) comprises a body of stratified sediments up to 250 meters in depth
that form a partial closure of the Churchill River at the site of the Muskrat Falls hydroelectric
project. The Spur is essentially a peninsula of natural land extending from the north bank of
the river to a rock knoll that will form the left abutment of the Muskrat Falls dam.
Figure 1-3 shows the latest LiDAR based ground topography and river bathymetry for the
Muskrat Falls site. The dashed lines in Figure 1-3 illustrate the extent of the finite element
models developed in this study. Summarizing, the modeled domain is a roughly squareshaped area approximately 1.65 kilometer long by 1.5 kilometer wide. The south end of the
model corresponds to the Rock Knoll and the north end extends beyond the three kettle
lakes.
Landslide scarps are visible along both upstream (U/S) and downstream (D/S) shorelines of
the North Spur as illustrated in Figure 1-3. In November 1978, a landslide occurred on the
3
downstream slope of the Spur involving about 1.0 million m of soil materials. The landslide
was triggered when an ice dam broke up D/S of the Spur leading to rapid drawdown of the
river level. Consequently, the stability of this natural landform during and after reservoir
impoundment is a major concern of the LCP.
In order to reinforce the Spur, stabilization works have been designed by SNC Lavalin Inc.
(SLI) including a cement-bentonite cut-off wall and till blanket on the U/S side of the Spur,
earthworks to reshape and create stabilizing berms on the D/S slope, D/S filters and finger
drains and pressure relief wells.
There is an existing pump well system on the Spur, which has been operating since its
installation in 1981.
1.1
Study Objectives
The objectives of this study were to:
•
investigate the initial North Spur groundwater seepage patterns;
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•
assess the impact of the construction works on piezometric levels through the body of the
Spur at various reservoir levels;
•
provide model data that can be used to validate the stabilization works design;
•
provide results that can be used to assess if the existing pumping system can be
discontinued after implementation of the stabilization works;
•
evaluate the effect of reservoir impoundment on the kettle lakes at the north end of the
Spur; and
•
provide a monitoring and forecasting tool of changes in the hydraulic pressure within the
geologic units of the Spur during construction, impoundment and operation.
The following sections of this report describe the 3D FE seepage model, its calibration and
the results of case studies that were run to achieve the study objectives.
A summary of the results are provided in Section 8.
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2.
Reference Documentation
Several site investigations and pump well and piezometer installations have been performed
at the North Spur since 1965. The most recent investigation program was carried in 2013 by
AMEC. The geological setting and hydrogeological conditions of the North Spur have been
discussed and assessed in several geotechnical reports, which are listed below. The reports
form part of the basis for the modeling described in this report.
•
Muskrat Falls Development. A report to the British Newfoundland Corporation Limited.
October 1965, Acres Canadian Bechtel.
•
Lower Churchill Consultants. Muskrat Falls Development. Geotechnical Review of 1965
layout. A report to the Gull Island Power Company Limited. June 1976.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. I: Engineering report, 1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. II: Appendices, 1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. III: 1979 Field exploration program-soils investigation-borehole logs & lab results,
1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. IV: 1979 Field exploration program-construction materials-test pits & trenches-logs &
lab results, 1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Dewatering System, Construction Report, Operation and Maintenance
Information, March 1982, Report No. 11.99.18, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Dewatering System, Engineering Assessment, March 1982, Report No.
11.99.18, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Hydroelectric project, Dewatering System Assessment and Rehabilitation,
Feb. 1997, Report No. P11759.01, Acres International Limited.
•
Muskrat Falls, Standpipe Piezometer Installation Program Report, Feb. 1998, Report No.
P11759.02, Acres International Limited.
•
Muskrat Falls Hydroelectric Development, Final Feasibility Study, Vol. 1. Engineering
Report, Jan. 1999.
•
Muskrat Falls Hydroelectric Development, Final Feasibility Study, Vol. 2, 1998
Geotechnical Investigations, Jan. 1999.
•
The Lower Churchill Project, MF 1260- Assessment of Existing Pumpwell System- July
2008.
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•
The Lower Churchill Project, MF 1271- Evaluation of Existing Wells, Pumps and Related
Infrastructure in the Muskrat Falls Pumpwell System, March 2010.
•
The Lower Churchill Project, MF 1272- Installation of New Piezometers in the Muskrat
Falls Pumpwell System, April 2010.
•
Muskrat Falls Geological Report, Part III, Photos for cores and site areas, 1979, LCP
Admin Rec. No. 202-120142-00019.
•
Geotechnical Investigations Report. 2013 Field Investigations- North Spur. Muskrat Falls
Hydroelectric Development. Lower Churchill Project. November 2013.
•
The Lower Churchill Project, Muskrat Falls, North Spur Stabilization Design Drawings,
Sept. 2012, SNC-Lavalin Newfoundland Ltd.
•
MF North Spur Layers, Catia -3D Geological Model, SNC-Lavalin Newfoundland Ltd
(provided to Hatch in Jan, 2014)
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3.
3.1
Hydrogeological Overview
Stratigraphy
The stratigraphy of the North Spur is summarized in the following sections from the ground
surface to bedrock, based on the reports listed in Section 2
3.1.1
Upper Sand
A sand layer covers the surface on the North Spur generally from El.60 m to El.45 m. This
layer mainly consists of compact to dense, grey fine to medium sand with low fines content.
The layer is mostly dry and well drained except for a perched water table above an underlying
clay to silty clay layer. No permeability tests have been performed in this layer. Based on
grain size distribution of the upper sand, a hydraulic conductivity can be estimated as
-4
approximately 1 x 10 m/s.
3.1.2
Stratified Drift
Stratified drift deposits have been observed from approximately El.45 m to El.0 m. The drift
consists of alternating layers of silty clay, and silty sand with occasional cleaner sand seams.
-7
A hydraulic conductivity of about 2.8×10 m/s was obtained from one falling head
permeability test in this layer during 2009 site investigations. Three pumping tests were
carried out in the stratified drift in 1981. The tests led to interpreted hydraulic conductivities of
-6
-7
-8
7.7×10 m/s, 1.3×10 m/s and 3.3×10 m/s for the southern, middle and northern blocks of
the North Spur, respectively.
-6
Laboratory permeability testing indicated a hydraulic conductivity in the order of 10 m/s for
the drift materials.
It should be noted that the hydrogeologic behavior of the stratified drift can be affected by the
presence of low permeable silty clay or clayey silt strata interbedded within the intermediate
sand layer.
3.1.3
Lower Marine Clay
Underlying the stratified drift zone is marine clay layer between approximately El.0 m to El.70 m. This layer mainly consists of low to medium plasticity slightly sensitive clay. Traces of
silt and sandy silt strata have been observed within the lower clay layer. No permeability tests
have been reported for this layer. Pumping tests and the piezometric response of
piezometers above and below this deposit indicated that the lower clay layer forms an
effective aquiclude at the North Spur site.
3.1.4
Lower Aquifer Layer
Below the marine clay is a deposit referred to as the lower aquifer. This unit consists of sand
and gravel with some cobbles and boulders and was generally observed from El. -70 m to the
bedrock surface, which varies in elevation. Pumping tests indicated an average hydraulic
-4
conductivity of about 1.4×10 m/s and the material generally has low fines content.
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3.1.5
Bedrock
The bedrock is generally granite gneiss with pegmatite intrusions. A series of water pressure
tests (packer testing) were performed at various depth intervals in boreholes drilled in the
bedrock across the site. Figure 3-1 shows the measured hydraulic conductivities versus
depth from 1979 packer tests in the bedrock. Based on Figure 3-1, the hydraulic conductivity
-5
-6
of the bedrock lies within the range of 10 m/s to 10 m/s for the upper portion of the bedrock
-7
(approximately 2-5 m). The hydraulic conductivity decreases with depth to between 10 to
-8
10 m/s. For this study, the bedrock is assumed to be an impermeable material relative to
the overlying units.
3.2
Hydrogeological Conditions
Numerous piezometers and wells have been installed at the site to characterize the
hydrogeological conditions. Details of pumping tests and piezometric monitoring data can be
found in the various site investigation reports issued between 1965 and 2003 (see
Appendix A). The following sections provide a brief summary of the existing hydrogeological
conditions based on site investigation information; including the aquifers and perched water
tables observed via piezometers and pumping tests.
3.2.1
Perched Water Level in the Upper Sand Layer
A perched water table was observed in the upper sand layer during the 1979 investigation.
This water table is mainly recharged by precipitation and water infiltration from the ground
surface.
3.2.2
Upper Drift / Intermediate Aquifer Deposits (IA)
An intermediate aquifer has been observed in the stratified drift throughout the Spur. The
Upper Drift is generally between El.0 m and El.45 m.
The North Spur drift deposits are observed to be saturated and are connected to the Churchill
River at both the U/S and D/S sides and are also recharged from the North-West side of the
Spur.
3.2.3
Lower Aquifer (LA)
Based on site investigations, a lower aquifer is generally found below El.-60 m and is mainly
composed of pervious sand and gravel with boulder/cobbles. The average thickness of this
aquifer is about 44 m in the vicinity of the North Spur. The LA was observed to connect to the
downstream side of the river via a deep depression in the bay immediately downstream of the
rock knoll (see Figure 1-3). The connection has been inferred due to measured piezometer
responses in the LA during a short term flooding event in 1979.
-4
The average hydraulic conductivity of the LA was about 1.4x10 m/s based on the 1979
pumping tests. A flow rate of about 18 l/s was estimated across an effective width of 1 km of
the aquifer at the D/S side of the North Spur.
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It should be noted that during the 1979 pump tests in the LA, the piezometric levels installed
in the IA did not change, which confirmed that there was no connection between the two
aquifers and that the lower marine clay layer acts as an aquiclude at the North Spur site.
3.3
Existing Stabilization Measures and Pumping Tests
3.3.1
Upper Drift / Intermediate Aquifer Deposits
In 1978, a major landslide occurred on the south end of the Spur reducing the maximum
width of the Spur in the vicinity of the rock knoll to about 80 m (initial width of approximately
200 m). Additional minor failures occurred in 1980-81. As a result of these incidents, a
dewatering and monitoring well system was installed in 1981 and the system has been
actively pumped since installation as a temporary slope stabilization measure.
Figure 3-2 illustrates the pump well system in the upper drift deposits. The system comprises:
•
22 pumped wells (pumping operation began in November 1981);
•
17 vibrating wire piezometers to monitor the pump drawdown;
During commissioning of the wells, two pumping tests were carried out between 1981 and
1983. The first pumping tests were relatively short-term tests and conducted in wells
numbered 3, 10, and 17, respectively. The second pumping tests were long-term tests from
1981 to 1983 and the 22 pump wells were operated continuously for 13 and 27 months,
respectively. A summary of pumping rates and durations for the pumping tests in 1981 and
1983 are provided in Tables 3-1 and 3-2, respectively. The pumping tests were used to
calibrate the 3D FE seepage model.
Table 3-1: Summary of Short Term Pumping Tests in Intermediate Aquifer (1981)
Well No.
Pumping Rate ( l/s)
Duration (min)
W3
1.25
4140
W10
0.13
520
W17
0.12
90
Table 3-2: Summary of Long Term Pumping Tests in Intermediate Aquifer (1981-1983)
Well No.
W1-W7
W8-W22
3.3.2
Pumping Rate ( l/min)
Duration (months)
56
10
13/27
13/27
Lower Aquifer
One pump test was carried out in the LA in 1979. Figure 3-3 illustrates the location of
piezometers and wells in the lower aquifer.
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3
During the LA pump test, Well F2 had been pumped for 6 days at a rate of 270 m / hour.
Based on the test records, dewatering system rehabilitation and assessments were
performed in 1996, 2008 and 2009, respectively.
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4.
Design Stabilization Measures
The following engineered stabilization measures have been designed to enhance stability of
the North Spur:
•
A diaphragm cut-off wall along the U/S toe of the Spur with a length of 900 m and a
maximum depth of 70 m. The cut-off wall penetrates 2 m into the lower marine clay
deposit;
•
A till blanket over part of the U/S slope of the Spur. The blanket crest level is at EI.
42.1 m;
•
Rock fill slope protection has been designed for both the U/S and D/S faces;
•
The geometry of the North Spur has been redesigned with berms at various elevations to
improve stability and manage erosion;
•
10 pressure relief wells are planned to be installed into the LA near the D/S toe of the
North Spur;
•
A deep transverse toe-drain will be built at the toe of the North Spur. The drain will
involve excavating and backfilling a deep ditch with pervious materials; and
•
A system of finger-drains will be installed on the downstream slope of the Spur.
The primary objectives of the stabilization works are to lower the piezometric level in the IA,
reduce infiltration from the U/S reservoir into the Spur (Cut-off Walls and Till blanket), capture
and provide filtered outlets for seepage water (D/S finger drains), improve the D/S slope
stability, and protect against erosion at the toe and on the slopes.
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5.
5.1
Modeling Methodology
Introduction
The finite element (FE) modeling described below was performed using the commercial
software FEFLOW 6.2. FEFLOW is commonly used for 3D seepage and contaminant
transportation analysis. The software was used in the seepage mode only for this study.
Two 3D FE seepage models were developed and analyzed. The FE models are based on the
3D geological model for the North Spur developed by SLI using the Catia software.
Nalcor provided the Catia model to Hatch and Hatch subsequently exported the model to
AutoCAD DXF format so that it could be imported into FEFLOW 6.2 for mesh generation.
Figure 5-1 shows the converted 3D DXF model. To review the accuracy of the Catia model,
six cross sections were created through the model and the resultant subsurface profiles were
compared to the latest site investigation data. Based on this review, it was concluded that:
•
the 3D Catia model is generally consistent with the latest geotechnical data; and
•
the model provides a good basis for development of 3D FEFLOW models of the site.
As discussed in Section 3, the lower marine clay layer acts as an aquiclude at the site; it
isolates the upper IA from the LA. Accordingly, two separate 3D FEFLOW models were
developed; one for the LA and a second model for the IA.
5.2
Model Layers and Extents
The model boundary extents were based on the 3D Catia model provided by SLI. The model
2
is approximately 2.5 km with extents previously shown in Figures 1-2 and 1-3. Although a
larger regional model domain would have been ideal, data was not available to develop such
a regional groundwater model. Furthermore, a regional groundwater model would not have
allowed the development of a detailed model for the site.
The regional component of the groundwater flow regime was accounted for by introducing
boundary inflows (i.e. fluxes) on the north and west sides of the model domain. The
magnitudes of the fluxes were varied until the in situ piezometric levels and gradients were
adequately modeled.
After impounding the reservoir, additional head will be exerted on the marine clay layer in the
river bottom U/S of the dam site leading to increased recharge to the LA. Locally, such
recharge is negligible but the cumulative leakage through the marine clay over the 16 km
reservoir length due to impounding should result in increased inflows to the model domain
from the west. To account for this, modeled inflows to the site from the west were introduced
and increased versus the reservoir level. Two-dimensional FE seepage models were
developed to estimate the increased leakage. One 16 km long model was developed to
estimate the influence of reservoir level on the LA inflows; a second 5.5 km long model was
used for the IA. Details of the 2D seepage models are summarized in Appendix B.
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Sensitivity analyses indicated that the reservoir level will have a significant impact on inflows
into both the LA and IA.
Seven (7) subsurface layers were modeled based on the 3D Catia model from the ground
surface to the bedrock surface. Figure 5-2 illustrates a cross-section showing the soil layers
within the model area.
Summarizing, the model extends to:
5.3

the mid-point of the rock knoll (Southern extent);

approximately 100 m north of the kettle lakes (Northern extent);

approximately 500 m U/S of the Spur centerline (Western extent);

approximately 200 m D/S of the Rock Knoll past the location of the scour hole in the
Churchill River bed (Eastern extent).
Meshing
Figures 5-3 and 5-4 illustrate the FE meshes for the LA and IA, respectively. The meshes
consist of triangular prism elements; the number of elements was 21,630 for the LA and
64,089 for the IA. The final number of elements is based on mesh sensitivity studies, which
were undertaken to ensure that the generated meshes provided sufficiently accurate
solutions. The outputs (e.g. changes in hydraulic heads, ΔH) were monitored during the mesh
analysis. A coarse mesh was examined first and then the mesh was refined until insignificant
changes were observed in the calculated hydraulic heads. In addition, finer meshing was
applied at the critical parts of the model such as near pump wells, the cut off wall, U/S
blankets, finger drains etc. Accuracy was the primary factor affecting the mesh density;
whereas the simulation time was not used as a basis for the number of elements.
5.4
Lower Aquifer Model
5.4.1
General
Two soil layers were included in the LA model as illustrated in Figure 5-3. The soil layers are
the Lower Marine Clay deposit (from El. 10m to El. -50 m); and the Lower Aquifer (Below El. 50 m to bedrock).
5.4.2
Material Properties
The hydraulic conductivity values of these layers were estimated based on the site
investigation data. Saturated flow properties were used in the 2D and 3D models.
Unsaturated flow was not considered due to the limited thickness of the vadose zone. The
storage properties (storativity) of materials were also neglected, which is appropriate for
modeling dams and/or long-term pump tests but less appropriate for short-term pump tests.
Table 5-1 summarizes the modeled hydraulic conductivity values for the LA and marine clay
layer.
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Table 5-1: Hydraulic Conductivity Values Used in Lower Aquifer 3D FEFLOW Model
5.4.3
Soil Layers
Hydraulic Conductivity
(m/s)
Lower Clay
Lower Aquifer
1.0x10
-4
1.4x10
-8
Boundary Conditions
Table 5-2 summarizes the boundary conditions assigned for the LA model. The boundary
conditions are also illustrated in Figures 5-5 to 5-8, inclusive. The following is a summary of
the modeled boundaries.
First, total head boundary conditions corresponding to the river water level were assigned to
the marine clay layer both U/S and D/S of the North Spur, see Figure 5-5.
The bedrock surface including the Rock Knoll was assumed to be a no-flow boundary, see
Figures 5-6 and 5-7.
A flux boundary was applied to the marine clay where the clay is overlain by the upper drift
deposits (see Figure 5-6). Additional flux boundaries were modeled on the west and north
ends of the model to account for inflows into the site from the regional groundwater system.
It is noted that piezometric levels in the LA are mainly governed by the north and west in-flow
fluxes.
As noted in a preceding section of this report, Appendix B describes how the inflows from the
regional groundwater system were estimated. Figure 5-8 illustrates the input fluxes at various
reservoir levels.
Table 5-2: Summary of the Boundary Conditions for Lower Aquifer 3D FEFLOW Model
Location
U/S Lower Clay Surface – Below
Riverbed
D/S Lower Clay Surface – Below
Riverbed
Lower Clay Surface Area under Upper
Drift Deposits
Boundary Condition
Figure
Total Head, Ht = 17.5m (existing conditions)
Fig.5-5
Total Head, Ht = 3.0m (existing conditions)
Fig.5-5
-11
Infiltration Rate, q = 6×10 m/s
Fig.5-6
North Side of Model, LA
Inflow Flux Boundary Q1 (based on function shown
in Figure 5-8)
Inflow Flux Boundary Q2
South Side of Rock Knoll
No Flow Boundary
Fig.5-6
Bedrock Surface
No Flow Boundary
Fig.5-7
West Side of Model, LA
Fig.5-6
Fig.5-6
Referring to Table 5-2, the input flux at the top of the marine clay layer (i.e. from the overlying
drift deposits) represents 0.2% of the average annual precipitation rate of 950mm/y. This flux
was included in the model primarily to account for and acknowledge all of the relative
hydrogeological inputs to the LA flow regime. There is a groundwater mound in the upper
North Spur where piezometric levels are higher than those in the LA. As such, there will be
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associated downward flow from the IA to the LA through the marine clay deposit. Based on
sensitivity analyses, however, the infiltration rate from the IA to the LA has an insignificant
impact on hydraulic head in the LA due to a very thick low permeable of the clay layer
The flux boundaries Q1 and Q2 in Table 5-2 were estimated using the FE model summarized
in Appendix B. Q1 represents regional groundwater inflow to the model domain from the west;
Q2 is from the north. Sensitivity analyses were carried out to examine the effect of the ratio
Q2/Q1. Values of Q2/Q1 equal to 0.05, 0.2 and 0.5 were examined. A value of 0.2 was found
to best model the natural gradients in the LA and direction of flow. The detailed sensitivity
analyses are summarized in Appendix C.
5.5
Upper Drift/Intermediate Aquifer Deposits (IA) Model
5.5.1
General
The finite element mesh for the IA Model included the following seven (7) soil layers:
•
Upper sand layer
•
Upper silty clay layer
•
Upper silty sand drift- Zone A
•
Lower silty clay layer
•
Lower silty sand drift- Zone B
•
Lower clay
•
Low permeable soil layer block the D/S scarp surfaces
Figure 5-4 shows the 3D finite element mesh and Figure 5-2 shows a cross section through
the IA.
5.5.2
Modifications to the Geologic Model
Currently, there are high piezometric levels present in the southern block of the Spur, which is
the most critical part of the study area. Model studies indicated that the high piezometric
levels cannot be attributed to surface infiltration alone.
Extensive analyses were performed to investigate causes to explain such high piezometric
readings in the southern block of the Spur. The analyses are summarized in Appendix D.
Based on the results summarized in Appendix D, it was concluded that the FEFLOW model
for the IA could only be calibrated if a layer of low permeable material (i.e. slide debris) was
modeled on the D/S surface of the Spur in the old failure scarps. This material within the slide
zones is thought to consist of low permeable slide debris from historical landslides. The slide
debris has apparently blocked seepage outlets on the D/S slope adjacent to the rock knoll
leading to the high piezometric readings.
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Figure 5-9 shows the extent of the modeled slide debris. The low-permeability materials at
the D/S surface of the Spur should be verified by a site investigation program during the early
stages of implementation.
5.5.3
Material Properties
The modeled hydraulic conductivity values for the upper drift layers were estimated from the
site investigation information. Saturated flow properties were used in the 2D and 3D models.
The unsaturated characteristics of the soils were not modeled (i.e. soil characteristic curves
were not specified for the vadose zone above the groundwater table).
The storativity of the aquifer materials was also neglected, which is appropriate for modeling
dams and long-term pump tests but less appropriate for short-term pump tests. As such,
more emphasis was placed on the long-term pump tests during calibration than the short term
tests.
Table 5-3 lists the modeled material parameters. It is noted that these are calibrated
parameters. Appendix D describes a series of sensitivity studies that were performed to
arrive at the final parameters.
Table 5-3: Hydraulic Conductivities Used in FEFLOW Model for Intermediate Aquifer
No.
Soil Layers
Hydraulic Conductivity, K (m/s)
1
Upper Sand
Kxx=Kyy=Kzz= 1x10
-4
2
Upper Silty Clay
Kxx=Kyy=Kzz= 1x10
-7
3
Upper Silty Sand Drift -Zone A
Kxx=Kyy=Kzz= 8x10
-6
4
Lower Silty Clay
Kxx=Kyy=Kzz= 1x10
-7
5
Lower Silty Sand Drift - Zone B
Kxx=Kyy=Kzz= 8x10
-6
6
Lower Marine Clay
Kxx=Kyy=Kzz= 1x10
-8
7
Low Permeable Soil Layer for Blockage of D/S
1
Scarp Surfaces
Kxx=Kyy=Kzz= 1x10
-8
1
Note: Layer 7, Slide Debris Material, was added in the Model based on sensitivity analysis. This layer should be
verified by excavating test pits during the site early works program.
5.5.4
Boundary Conditions
The boundary conditions for the IA model are summarized in Table 5-4 and discussed below.
First, total head boundary conditions were assigned to the riverbed U/S and D/S of the North
Spur (Spur). Additionally, a seepage face boundary was defined for the riverbank slopes and
U/S and D/S slopes of the Spur. The “built- in” seepage face feature in FEFLOW (Hydraulic
Head (BC)) was assigned to nodes on the U/S and D/S faces of the model. The seepage
face boundary treatment in FEFLOW is similar to that found in the 2D Seep/W program.
Initially, nodes on the seepage face are assumed to be no-flow boundaries and the seepage
equations are solved. If a positive pressure is found to have built up at a given node on the
seepage face, then the node is converted to a discharge boundary by setting the total head
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equal to the elevation head of the node; pressure head is zero. The flow equations are
resolved and an iterative solution scheme is followed to converge on the final extent of the
seepage face. Figure 5-10 illustrates the total head and seepage face boundaries.
No flow boundaries were defined at the bottom of the model representing the underlying
marine clay layer, and on the south side of the model near the river centerline representing a
groundwater divide between the north and south sides of the river (see also Figure 5-10).
Finally, three flux boundary conditions were defined to account for the various hydrogeologic
-9
inflows into the model as illustrated in Figure 5-11. A surface flux of 1.2×10 m/s was applied
to the ground surface to account for infiltration. This represents 4% of the annual
precipitation of 950mm/year combined with a runoff coefficient of 0.9, and 6% evapotransportation, which is considered to be reasonable. Notwithstanding the preceding
discussion, the infiltration rate is not a major driving factor for piezometric conditions in the
Spur after impoundment.
In addition, the model boundary extents are small relative to the regional hydrogeology. As
such, flux boundaries were specified at the west and north sides of the model to account for
regional groundwater inflows to the study domain. Appendix B describes how the regional
inflows or fluxes were estimated. Figure 5-12 illustrates the modeled input flux into the IA
versus reservoir levels.
Table 5-4: Summary of the Boundary Conditions of 3D FEFLOW Model for Intermediate Aquifer
Area
Initial Boundary Condition
Figure
U/S River Bed
D/S River Bed
Surface of the North Spur
Total Head Ht=17.5 m (existing conditions)
Total Head Ht=3.0 m (existing conditions)
1
Infiltration Rate, q=1.2e-9m/s
Inflow Flux Boundary Qw (based on the function
shown in Figure 5-12)
Inflow Flux Boundary QN= QW
No flow Boundary
Potential Seepage Face
Potential Seepage Face
Potential Seepage Face
Fig.5-10
Fig.5-10
Fig.5-11
West Side of Model, IA
North Side of Model, IA
South Side of Model, IA
U/S Spur Slope Surface
Kettle Lakes Surface
D/S Surface of Spur
Note:
1-
Fig.5-11
Fig.5-11
Fig.5-10
Fig.5-10
Fig. 5-10
Fig.5-10
The Infiltration rate of q=1.2e-9 m/s into the spur surface is assumed to be 4% of the annual
average precipitation rate of 950 mm/y. Sensitivity analyses indicated that the infiltration rate is not
driving factor.
5.5.5
Modeling Approach - Stabilization Measures, Pumping, and Pressure Relief Wells
The following approach was used to model the cut off wall, U/S blanket, finger drains and
pumped wells:
•
The cutoff wall was modeled as an impermeable surface; whereas, the till blanket was
-8
modeled as a low permeable layer (k=10 m/s) using continuum elements;
•
Finger drains were modeled as a high permeable material zone. The thickness, depth
and location of the zones were established from the SLI design drawings. A table was
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generated from the design drawings of X, Y and Z ASCII data representing the finger
drain location and elevation. These coordinates were imported to FEFLOW and used to
regenerate the mesh locally to account for the drains.
•
Relief wells were modeled using discrete feature elements in FEFLOW. For such
elements, the cross section and conductivity (high permeable materials) are assigned. If
a high conductivity is assigned, the elements model a preferred path of seepage from the
model with reduced head loss. The number and location of relief wells were determined
as per the design drawings except as noted below.
•
Multilayer well features were used to represent the pump well system, which intercept a
number of the layers in the upper drift deposits. Parameters were assigned for the
multilayer wells including top and bottom elevation, radius of the well, pumping rate and
duration.
•
Transient solutions were simulated in FEFLOW (problem setting) by providing initial
simulation time, final time, and time step size. The program defaults were employed.
•
As noted above, the saturated flow region dominates and was the main focus of this
study particularly for the IA because the LA is in a saturated state. As a result, the
saturated mode was used in the analysis. The default convergence parameters in
FEFLOW were used to solve the non-linear flow equations, which include the
convergence error and the maximum number of iterations per time step.
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6.
Calibration Results
6.1
Lower Aquifer
Three calibrations were performed for the LA model. The calibration cases, which are listed in
Table 6-1 included:
•
Case C-1: The existing conditions (i.e. Current and historic piezometric levels);
•
Case C-2: The 1979 pumping tests in the LA; and
•
Case C-3: The LA response during a flood event in 1979 (i.e. the River level raised by
2.82 m).
For calibration Case C-3 (see Table 6-1), the Churchill River level increased by 2.82 m in
about 10 days (see SNC Lavalin Report entitled: Hydrogeology of the site, SNC-LAVALIN
Newfoundland Ltd., Volume 2, Appendix 4). The time-dependent increase and decay of the
river level observed during this event was modeled as a validation exercise.
Table 6-1: Summary of the Conditions for Lower Aquifer Model Calibration
River Level El. (m)
Pumping Test
FEFLOW
Modeling
3
N/A
17.5
3
Diameter=40.6 cm
Tip level= El. -108 m
Pump Rate = 270
3
m /hr
Duration= 6 days
Steady Seepage
Analysis
Rising 2.82 m
Rising 1.9 m
N/A
Case
Description
U/S
D/S
C-1
Existing
Condition
17.5
C-2
Pumping Test in
LA
C-3
River Level
Increase
6.1.1
Transient
Seepage
Analysis
Transient
Seepage
Analysis
Existing Conditions (Case C-1)
Table 6-2 summarizes calculated and measured piezometric levels at piezometer locations in
the lower aquifer corresponding to the existing conditions. Figure 6-1 illustrates the calculated
piezometric head contours.
Referring to Table 6-2, there is generally good agreement between measured and calculated
piezometric levels for the existing conditions. At most of the piezometer locations, the
difference between the model and measurement is less than 4%. At piezometer E1 however,
the difference was 26.7%. The piezometric level at E1 could not be matched without
sacrificing accuracy at other more important piezometer locations closer to the Spur. It is
believed that local heterogeneity is causing the error. The mean absolute error (mean error)
including all piezometers is about 6.3%, which is considered to be reasonable.
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Table 6-2: LA Calibration Results for the Existing Conditions
Piezometers Installed
1
in LA in 1979
Existing Condition (C-1)
Piezometric Readings
(m)
Calculated Values
(m)
Error
%
F2
5.4
5.5
1.8%
P1
5.4
5.6
3.6%
A1
7.0
6.9
-1.5%
B7
4.2
4.1
-2.4%
D5
5.5
5.6
1.8%
4.4
6.0
26.7%
E1
Mean Absolute Error
Note:
6.1.2
1-
6.3%
These observation wells are all the wells that were available at this stage.
Lower Aquifer Pump Test (Case C-2)
Figure 6-2 shows the location of Well F2 that was installed in the LA for the 1979 pumping
tests. Figure 6-3 shows the modeled Well F2 and Table 6-3 compares calculated and
measured drawdown values at piezometers installed in the LA. The corresponding calculated
and measured drawdown cones are illustrated in Figure 6-2.
Based on Figure 6-2 and Table 6-3, it is evident that there are areas of good and poor
agreement between the calculated and measured drawdown during the 1979 pumping test.
First, the calculated and measured drawdown at piezometers P1, B7 and E1 are typically
within 15%, which is considered to be reasonable; whereas, at F2, A1 and D5, there is
considerable error ranging from 28.9% to 81.5%. The error associated with F2 is considered
to be predictable because the seepage model does not account for well losses. As such, one
would expect the measured drawdown to exceed the calculated value. However, the errors at
A1 and D5 (up to 81.5%) are attributed to the anisotropy and heterogeneity of the LA, which
has been highly idealized in the modeling. Although the mean error is 26.5% considering the
plus-minus nature of the errors, the calculated drawdown cone fits within the measured
values, which Hatch considers to be reasonable given the simplified stratigraphy in the
model. The actual drawdown cone appears to be ellipsoid in shape with the elongated axis
toward the east-west direction. The numerical drawdown cone is symmetric due to the
isotropic model and parameters used.
Reiterating, the FE model is judged to be sufficiently accurate and discrepancies between the
measured and calculated drawdown during pumping are considered to be due primarily to
heterogeneity and anisotropy in the aquifer and the neglecting of head losses at the pumped
well (F2).
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Table 6-3: Summary of the Results for Pumping Test in 1979 from Lower Aquifer 3D FEFLOW
Model
Calculated from 3D FEFLOW model
Hydraulic Head
Drawdown
after Pumping Test
(m)
(m)
Piezometers
Installed in LA in
1979
Measured
Drawdown in 1979
Pumping Test (m)
F2
20.4
-9.0
14.5
-28.9%
P1
7.19
-1.8
7.4
2.6 %
A1
1.9
3.2
3.6
81.5%
B7
2.1
2.5
1.8
-14.3%
D5
2.16
2.8
2.8
29.6%
E1
1.84
4.2
1.8
-2.2%
Mean Absolute Error
6.1.3
Error (%)
26.5%
Validation Case (Case C-3)
Table 6-4 compares the calculated and measured piezometric responses to a 2.82 m rise of
the river level in about 10 days during a flood event in the early 1980s. Based on Table 6-4,
the calculated error varies between 4.6% and 54.6% and the mean absolute error is 27.6%.
Again, the difference is considered to be satisfactory for this modeling exercise and c an be
attributed to anisotropy and heterogeneity, which have been neglected. It is noted that there
is also uncertainty with regards to the accuracy of the river level and piezometer readings for
this case.
Table 6-4: Summary of the Results for Piezometric Response Due to River Level Increase in 1979 from Lower
Aquifer 3D FEFLOW Model
Piezometer No.
Piezometric Response of Rising (m)
Measured
Calculated Readings- FEFLOW
Error
%
A1
N/A
0.75
N/A
F2
N/A
1.20
N/A
P1
1.10
1.05
4.6%
D5
1.50
1.10
26.7%
E1
1.30
0.98
24.6%
B7
1.30
2.01
-54.6%
Mean Absolute Error
27.6%
Based on the preceding discussions and comparisons, it is concluded that the model is
adequately calibrated and suitable for investigating the general response of the LA during
reservoir impoundment.
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6.2
Upper Drift and Intermediate Aquifer (IA)
Table 6-5 lists the calibration cases used for the upper drift (IA) seepage model. The cases
include:
•
Case C-4: Existing conditions, i.e. Historical piezometer levels prior to pumping from the
dewatering system (Case C-4);
•
Case C-5: 1981 short-term pumping test in the IA (Case C-5);
•
Case C-6: Long-term pumping tests during 1981 to 1983; 13 months and 27 months
duration, respectively (Case C-6).
Table 6-5: Summary of the Conditions for Intermediate Aquifer Model Calibration
River Level
El. (m)
U/S
D/S
Case
Description
C-4
Existing Condition
17.5
C-5
Pumping Test in IA
C-6
Pumping Test in IA
6.2.1
Pumping Test
FEFLOW Modeling
3
N/A
Steady Seepage Analysis
17.5
3
Short term
Transient Seepage
Analysis
17.5
3
Long-term for 13 and
27 months pumping
between 1981-1983
Transient Seepage
Analysis
Existing Conditions (Case C-4)
Table 6-6 compares calculated and measured piezometric levels for the upper drift deposits
prior to operating the pump well dewatering system. Figure 6-4 illustrates contours of
calculated piezometric head in the IA.
Referring to Table 6-6, the error between measured and calculated piezometer levels in the
upper drift deposit (IA) varies between 0.4% at piezometer P14 and 21.4% at piezometer E1.
The mean absolute error is 7.2%, which is quite good and most monitoring points are within
10% of the readings. Agreement between the measured and calculated piezometric levels is
very good for the southern block of the Spur. The error for this important part of the Spur is
within 5.0%. It is acknowledged that there is more error associated with the north area of the
Spur. The northern block (kettle lakes area) of the model was considered less critical than
southern part during calibration. This is considered as the best match taking into
consideration the budget and available data.
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Table 6-6: Calculated and Measured Initial Conditions in the IA
Piezometer
Measured Hydraulic
Head (m)
Calculated Hydraulic Head
from FEFLOW Model (m)
Error (%)
B6
39.40
38.80
1.5%
E1
27.60
33.50
-21.4%
D4
25.00
29.50
-18.0%
B5
32.50
28.90
11.1%
C4
1
26.30
27.30
-3.8%
C3
1
27.20
26.30
3.3%
D1
1
28.20
26.80
5.0%
B8
1
24.20
26.00
-7.4%
P2
24.95
26.50
-6.2%
P3
30.84
26.80
13.1%
P4
28.91
27.20
5.9%
P5
28.17
27.40
2.7%
P6
26.57
27.60
-3.9%
P14
26.40
26.30
0.4%
P15
28.00
26.70
4.6%
P17
29.03
27.10
6.6%
Mean Absolute Error
7.2%
1-
Note: The highlighted piezometers are installed in the drift within the southern block of the Spur and the mean
absolute error for these piezometers is 4.87%.
6.2.2
Short-term Pump Test (C-5)
Table 6-7 compares calculated and measured piezometer levels during the short term pump
tests conducted in 1981. Figure 6-5 illustrates calculated contours of piezometric head. The
short term tests involved the following pump rates and durations:
3
•
Well W3: 108 m /day for 69 hrs
•
Well W10: 11.23 m /day for 8 hrs and 40 min
•
Well W17: 10.37 m /day for 1.5 hrs.
3
3
Based on Table 6-7, errors between calculated and measured drawdown during the shortterm pumping varies between 6.7% and 86.8%. The mean absolute error is 35.6%. It is noted
that most of the error occurs in piezometers situated very close to the pump wells; whereas,
the error decreases with distance from the wells. In general, differences between the
calculated and measured piezometric response can be attributed to heterogeneity and
anisotropy in the upper drift deposits. The stratigraphy of the upper drift deposits has been
highly idealized and a 35.6% average absolute error is considered to be reasonable. The
error is typically less than 14.8% (i.e. the mean error for W2, W3 and W4 during pumping test
in W3) in the southern block of the Spur, which is more critical than the northern part of the
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Spur. Some of the discrepancy between measured and calculated behavior could also be
due to neglecting the storativity of the aquifer materials. As discussed in Section 5, the
aquifer storage parameters were neglected, which is important during short term pumping but
less critical during long-term pumping, which is described below in Section 6.2.3.
Table 6-7: Summary of the Results for Short-term Pumping Test Based on FEFLOW Modeling
Calculated Hydraulic Head (m)
Piezometer
Error (%)
Before
Pumping
After
Pumping
Drawdown
Drawdown
W1
26.3
25.8
0.5
0.3
66.7%
W2
26.5
24.6
1.9
2.14
W3
26.6
20.8
5.8
6.44
W4
26.7
24.9
1.8
1.46
W5
26.9
25.9
1.0
1.9
W6
26.9
26.5
0.4
0.81
W7
27.4
27.1
0.3
0.38
P1
26.2
26.1
0.1
0.13
P2
26.5
26
0.5
0.32
P3
26.7
25
1.7
1.28
P4
26.8
25.8
1.0
1.88
P5
27.2
27
0.2
1.51
-11.2%
-9.9%
23.3%
-47.4%
-50.6%
-21.1%
-23.1%
56.3%
32.8%
-46.8%
-86.8%
33.3%
-44.8%
-6.7%
9.8%
35.6%
P6
27.7
27.5
0.2
0.15
P15
26.7
25.7
1.0
1.81
P16
26.8
26.1
0.7
0.75
P17
27
26.1
0.9
0.82
Mean Absolute Error
6.2.3
1981 Measurement
(m)
Long-term Pump Test (C-6)
Lastly, Table 6-8 compares calculated and measured piezometric levels for the long-term
pump tests in the upper drift deposit. Figures 6-6 and 6-7 illustrate the calculated piezometric
contours for the 13 and 27 month pumping tests, respectively. The long-term tests had the
following pump rates and durations:
3
•
Wells W1-W7: 80.64 m /day
•
Wells W8-W22: 14.4 m /day
3
The drawdown was measured after 13 and 27 months of pumping. It is noted that the
comparison in Table 6-8 is complicated by the long-term duration of the pump tests. Over the
test period, background piezometric levels would have fluctuated due to seasonal variations
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in precipitation. However, the field records for these tests are insufficient to accurately
quantify seasonal variations. As such, there is significant error (plus and minus) associated
with piezometers that exhibited little to no response during the testing. These piezometers are
ignored in Table 6-8 and noted as NA (not applicable). Furthermore, temporary outages of
the pump system can also have a significant impact on the drawdown. Outages were not
accounted for in the numerical model.
Accounting for the difficulties noted above, the error between measured and calculated
drawdown during the long-term pump tests varied between 4.3% - 78.6% for the 13 months
duration and 1.6% - 99.2% for the 27 months duration. The corresponding absolute mean
errors are 34.8% and 39.0%, respectively.
Table 6-8: Summary of the Results for Long-term Pumping Tests Based on FEFLOW Modeling
3
3
Pump Rate: W1-W7: 80.64 m /day; W8-W22: 14.4 m /day
After 13 months
After 27 months
Piezometer
Calculated
Drawdown
(m)
Measured
Drawdown
(m)
Error
(%)
Calculated
Drawdown
(m)
Measured
Drawdown
(m)
Error
(%)
P1
7.7
0.3
NA
9.9
1.2
NA
P2
13.3
12.45
6.8%
14.4
13.85
4.0%
P3
14.5
11.19
29.6%
16.0
12.44
28.6%
P4
14.2
17.91
-20.7%
16.4
-
-
P5
11.7
16.87
-30.6%
22.2
18.97
17.0%
P6
7
3.92
78.6%
9.5
4.77
99.2%
P7
5
2.8
78.6%
6.3
3.35
88.1%
P8
4.7
4.91
-4.3%
5.65
5.56
1.6%
P9
3.4
0.65
NA
4.2
0.4
NA
P10
2.9
0.14
NA
3.6
0.39
NA
P11
1.8
0.19
NA
2.5
0.49
NA
P12
1.6
-0.25
NA
2.3
-0.3
NA
P13
3.5
1.33
NA
4.3
1.38
NA
P14
1.8
0.1
NA
2.5
0.3
NA
P15
13.9
19.14
-27.4%
15.9
19.69
-19.2%
P16
10.8
8.1
33.3%
12.8
8.8
45.5%
10.1
7.32
38.0%
12.0
8.08
P17
Mean Absolute Error
6.3
34.8%
Mean Absolute Error
48.5%
39.0%
Summary
Considering the effects of heterogeneity, anisotropy, and variations in the infiltration and
background piezometric levels during short and long-term pumping tests, the comparisons
between calculated and measured drawdown in Sections 6.1 and 6.2 are considered to be
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adequate and they substantiate the model for its intended purpose. The following
summarizes the calibration findings:
•
Both IA and LA models match existing piezometer readings within 6.3% and 7.2% mean
error, respectively.
•
For pump tests in the LA, the mean error between calculated and measured drawdown is
26.5%. The majority of this is due to poor agreement between one of the monitoring
piezometers (A1). Excluding A1, which is considered an outlier, the mean error is less
than 15%.
•
Based on the preceding points, the LA model is considered to be reasonably well
calibrated.
•
For short and long-term pump tests in the IA, the mean errors between calculated and
measured drawdown were between 34.8% (13 months pumping) to 39% (27 months
pumping), respectively. The errors are considered to be satisfactory considering the
effects of heterogeneity, variations in infiltration and background piezometric levels in the
Spur and pump outages during long-term pump operating.
•
The IA model is also considered to be adequately calibrated.
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7.
Model Predictions
7.1
Lower Aquifer (LA)
7.1.1
General
The primary objectives for modeling the LA were:
•
to assess the effect of pressure relief wells at the Stage 1 and Final Stage reservoir
levels; and
•
to provide predictions of piezometric heads in the aquifer after impoundment.
Table 7-1 summarizes the model runs (LA-0 to LA-4) that were performed for the lower
aquifer. Figure 7-1 illustrates the modeled relief wells. During development of the FE mesh for
the lower aquifer, four relief wells (RW A – D) were found to be in bedrock rather than in the
lower aquifer. Consequently, the relief wells were shifted north to ensure that the lower
aquifer was intercepted by all wells; Table 7-2 lists the revised pressure relief well
coordinates.
Table 7-1: Summary of the Case Studies for 3D FEFLOW Modeling of Lower Aquifer
Water Level El. (m)
Case
D/S Pressure Relief Wells
U/S
D/S
LA-0
17.5
3
LA-1
25
3
None
LA-2
25
3
10 Relief Wells (see Table 7-2 for coordinates)
LA-3
39
3
None
LA-4
39
3
10 Relief Wells (see Table 7-2 for coordinates)
None
1
Table 7-2: Summary of the Updated UTM Coordinates of Relief Wells in 3D FEFLOW Model
Relief Well
Easting (x)
Northing (y)
A
648586
5902811
B
648585
5902841
C
648587
5902871
D
648591
5902901
E
648594
5902931
F
648594
5902974
G
648594
5903004
H
648594
5903034
I
648594
5903064
648594
5903094
J
1
Note: The tip of the relief wells penetrate 5m into the LA layer and extend to the top elevation of El. 7.0
m corresponding to the existing ground surface.
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7.1.2
Do Nothing Case
Table 7-3 presents the calculated piezometric levels at the existing LA piezometers (F2, P1,
A1, B7, D5 and E1) corresponding to U/S water levels of El.17.5 m, El.25 m and El.39 m. The
results are for no pressure relief wells in the lower aquifer, which is referred to as the Do
Nothing case. The corresponding piezometric contours are illustrated in Figures 6-1, 7-2 and
7-3 for reservoir levels at El.17.5, El.25 m and El.39 m, respectively.
Based on Table 7-3, raising the reservoir level to
•
El. 25 m causes piezometric levels to increase between 1.3 m and 3.1 m compared to
existing conditions. The average rise is 2.2 m;
•
El. 39 m causes piezometric levels to increase between 2.8 m and 7.5m compared to
existing conditions. The average rise is about 5.2 m.
Table 7-3: Calculated Piezometric Head in Lower Aquifer – No Relief Wells
Piezometer
No.
Case LA-0
Calculated
Hydraulic Head @
U/S WL= El.17.5 m
F2
P1
A1
B7
D5
E1
Figure
5.5
5.6
6.9
4.1
5.6
6.0
Fig. 6-1
Case LA-1
Calculated
Hydraulic Head @
U/S WL= El.25 m
7.6
7.7
10.0
5.4
7.7
8.5
Average rise level (m)
Fig. 7-2
∆H (m)
1
2.1
2.1
3.1
1.3
2.1
2.5
2.2
Case LA-3
Calculated
Hydraulic Head @
U/S WL= El.39 m
10.3
10.5
14.4
6.9
10.8
12.0
Average rise level (m)
Fig. 7-3
Note: -∆H is the change between the calculated head compared to the existing (i.e. U/S water level of
1
El. 17.5 m)
7.1.3
Pressure Relief in the Lower Aquifer
Tables 7-4 and 7-5 summarize the calculated piezometric heads at the piezometers and
proposed relief well locations, respectively, for the case where 10 pressure relief wells are
installed in the lower aquifer. The relief well outlets are at El. 7.0 m.
Referring to Tables 7-4 and 7-5, the modeled results indicate:
•
When the U/S water level is raised to El. 25 m, the piezometric levels increase between
1.3 m and 3.1 m compared to existing conditions. The average rise is 2.2 m.
•
When the U/S water level is raised to El. 39 m, the piezometer levels rise between 2.8 m
and 7.5 m compared to existing conditions. The average rise is about 5.2 m.
•
The preceding results are identical to the Do Nothing case.
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∆H (m)
1
4.8
4.9
7.5
2.8
5.2
6.0
5.2
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•
When the U/S water level is raised to El. 25 m, the calculated piezometric heads at the
relief wells vary from El. 5.37 m to El. 5.47 m; this is below the outlet elevation at El. 7.0
m corresponding to the ground surface.
•
When the U/S water level is raised to El. 39 m, the calculated piezometric heads in the
relief wells vary from El. 6.84 m to El. 7.0 m; again, these levels are below the outlet
elevation at El. 7.0 m corresponding to the ground surface.
Summarizing, provided the model assumptions are correct and the lower aquifer is confined
under a continuous thick layer of low permeability marine clay, then relief wells should not be
required for the lower aquifer.
Piezometric levels (calculated) at the proposed pressure relief well locations in the lower
aquifer should rise from about El. 4.3 m corresponding to the existing conditions to El. 5.4 m
and El. 6.9 m corresponding to U/S water levels of El. 25 m and El. 39 m, respectively.
Since the proposed outlets for the relief wells are between El. 7.0 m to El. 8.5 m, the pressure
relief wells will have no impact on piezometric levels in the North Spur after impoundment
unless a siphon system is employed or the outlet can be lowered below El. 4.0 m
(approximately).
Significant deviations from these results may indicate either leakage through the marine clay
deposit somewhere upstream of the hydroelectric development, leakage into the lower
reservoir through fractured rock at the Muskrat Falls site, or that the confining layer has
limited lateral and U/S continuity.
Table 7-4: Calculated Head in the Lower Aquifer – With Installation of 10 Relief Wells
Piezometer
No.
Case LA-0
Calculated
Hydraulic Head @
U/S WL= El.17.5 m
F2
P1
A1
B7
D5
E1
Figure
5.5
5.6
6.9
4.1
5.6
6.0
Fig. 6-1
Case LA-2
Calculated
Hydraulic Head @
U/S WL= El.25 m
7.6
7.7
10.0
5.4
7.7
8.5
Average rise level (m)
N/A
∆H (m)
1
2.1
2.1
3.1
1.3
2.1
2.5
2.2
Case LA-4
Calculated
Hydraulic Head @
U/S WL= El.39 m
10.3
10.5
14.4
6.9
10.8
12.0
Average rise level (m)
N/A
∆H (m)
1
4.8
4.9
7.5
2.8
5.2
6.0
5.2
Note: ∆H is the change between the calculated head compared to the existing (i.e. U/S water level of
1
El. 17.5m)
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Table 7-5: Calculated Head in Lower Aquifer at the Relief Wells
Relief Well
Case LA-0
Calculated Head (m)
@ U/S WL= El. 17.5 m
Case LA-2
Calculated Head (m) @
U/S WL= El. 25 m
Case LA-4
Calculated Head (m) @
U/S WL= El. 39 m
A
B
C
D
E
F
G
H
I
J
Average Value
4.29
4.30
4.31
4.31
4.31
4.32
4.33
4.34
4.34
4.34
4.30
5.37
5.39
5.39
5.39
5.41
5.43
5.44
5.46
5.46
5.47
5.40
6.84
6.87
6.87
6.87
6.86
6.91
6.94
6.96
6.96
7.00
6.90
7.2
Upper Drift/Intermediate Aquifer Deposits (IA)
7.2.1
Cases Analyzed
Table 7-6 summarizes the analyses conducted for the IA. The following sections provide
details on the stabilization measures.
7.2.2
Stabilization Measures
Cut-off Wall
Figure 7-4 illustrates the modeled U/S cut-off wall. The cut-off wall extends from the
centerline of the FE model near the Rock Knoll to the north riverbank along the upstream toe
of the Spur. At the riverbank, the cut-off wall turns North-West heading toward the kettle
lakes.
The wall is designed to penetrate 2 m deep into the lower marine clay. The cut-off wall was
modeled using impermeable elements since the permeability (K) of the plastic concrete (i.e.
-9
K=1×10 m/s) is several orders of magnitude lower than the intermediate aquifer and drift
layers.
U/S Till Blanket
Figure 7-4 also illustrates the modeled U/S till blankets. The blanket was modeled using
continuum elements; the geometry conforms closely to the design geometry.
D/S Finger Drains
Three finger drains will be constructed on the D/S slope of the North Spur within the area of
the slide scarp. The finger drains are intended to penetrate through the slide debris in the
scarp to re-establish drainage exits on the downstream slope. Figure 7-5 illustrates the
modeled finger drains, which penetrate 1m into the modeled slide debris and have a
-3
permeability (K) of 1x10 m/s.
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Existing Pump Wells System
The existing pump well system (22 pump wells) was assessed as part of the stabilization
work. Pumping rates of 56 l/min and 10 l/min were adopted for wells W1 to W7 and W8 to
W22, respectively.
Table 7-6: Summary of Case Studies of Intermediate Aquifer Model
Stabilization Elements
Case
U/S WL
IA-0-a
D/S WL
COWs
Blankets
Finger Drains
Pump Wells




17.5
3
IA-0-b
17.5
3




IA-0-c
17.5
3




IA-1
25
3




IA-2
25
3




IA-3
25
3




IA-4
25
3




IA-5
25
3




IA-6
39
3




IA-7
39
3




IA-8
39
3




IA-9
39
3




IA-10
39
3




7.2.3
Results for Reservoir Impoundment without Stabilization Works (Do Nothing)
Table 7-7 summarizes the predicted response of the IA during U/S reservoir impoundment for
cases where the U/S cut-off wall, U/S blanket and D/S finger drains are not implemented and
the pump well system is off (see Case IA-0-a, IA-1 and IA-6 in Table 7-6).
Summarizing:

At the Stage 1 U/S water level (El. 25 m), the average increase in piezometric head
(Havg) in the southern block is about 1.3 m compared to existing conditions (Note: Havg
= 1.0m for all piezometers). Figure 7-6 shows the calculate piezometric contours;

At an U/S water level of El. 39 m, the calculated average rise of hydraulic heads is about
9.8 m in the southern block (Havg = 6.7m for all piezometers); Figure 7-7 shows the
corresponding calculated piezometric contours;
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Table 7-7: Calculated Piezometric Heads in the IA – Without Stabilization Measures
Case Study
Piezometer
IA-0-a
U/S WL=El. 17.5m
IA-1
U/S WL= El. 25 m
∆H (m)
B6
E1
D4
B5
1
C4
1
C3
1
D1
38.8
33.5
29.5
28.9
27.3
26.3
26.8
39.8
34.1
29.8
29.5
28.6
27.6
28.1
1
26.0
26.6
B8
Average
Hydraulic
Head in
Southern
Block
Figure
Fig. 6-4
IA-6
U/S WL= El. 39 m
∆H (m)
1.0
0.6
0.3
0.6
1.3
1.3
1.3
43.9
36.3
31.2
33.8
37.4
36.9
36.3
5.1
2.8
1.7
4.9
10.1
10.6
9.5
27.3
1.3
35.1
9.1
27.9
1.3
36.4
9.8
Fig. 7-6
2
2
Fig. 7-7
1
Note: The highlighted piezometers (C4, C3, D1, and D8) are installed within the southern block of the
Spur. ∆H is the change between the calculated head compared to the existing (i.e. U/S water level of
2
El. 17.5m)
7.2.4
7.2.5
Reservoir at El. 17.5m – with Pump Well System
Table 7-8 summarizes predicted piezometric levels in the upper drift deposits corresponding
to existing U/S and D/S water levels. The analysis was undertaken to study the impact of the
pumped well system (Case IA-0-b).
•
Referring to Table 7-8, without the pumped well system and finger drains, piezometric
heads in the upper drift deposits are high. The average piezometric level in the southern
block of the Spur is about El. 26.6 m corresponding to the existing condition. Figure 6-4
shows the calculated hydraulic head contours.
•
With operating the pump well system, the piezometric levels drop. The average
piezometric head in the south block of the Spur drops to about El. 17.5 m (i.e. an average
drop of about 9.1 m). Taking into account all piezometers, the corresponding drop is
about 5.3 m. As such, the existing pump well system significantly lowers the piezometric
levels in the southern block of the Spur, which is considered as the most critical part of
the North Spur. Figure 7-8 shows the calculated hydraulic head contours.
Reservoir at El. 17.5m – with Finger Drains and Pump Well System
Table 7-8 also summarizes the analyses undertaken to study the impact of the finger drains
and pumped well system.
•
After installation of the D/S finger drains, the piezometric levels drop. The average head
in the south block of the Spur drops to about El. 20.7m (i.e. a drop of about 5.9m). Taking
into account all piezometers, the corresponding drop is about 3.5 m. As such, the D/S
finger drains also have a significant impact on lowering the piezometric levels in the
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southern block of the Spur; however, the impact is less than the pumped well system.
Figure 7-9 shows the calculated hydraulic head contours.
•
After installation of the D/S finger drains with operation of the existing dewatering system,
the average head in the south block of the Spur drops to about El. 10.7m (i.e. a drop of
about 15.9m). Taking into account all piezometers, the corresponding drop is about
8.9 m. Figure 7-10 shows the calculated hydraulic head contours.
It is concluded that the finger drain system will help to reduce piezometric head in the North
Spur but the drains are less efficient than the existing pumped well system. There is
significant drawdown of the piezometric head in the North Spur when both the wells are
pumped and finger drains operative.
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Table 7-8: Calculated Piezometric Heads at the U/S WL of El.17.5m with Finger Drains and the Existing Dewatering System
U/S WL at El. 17.5 m
Hydraulic Head
Before
Stabilization
(IA-0-a)
Piezometer
With Pumping Well System
(IA-0-b)
With Finger Drains
(IA-0-c)
Hydraulic
Head (m)
∆H (m)
Hydraulic
Head (m)
∆H (m)
2
2
With Finger Drains and
3
Pumping
(IA-0-c)
Hydraulic
2
∆H (m)
Head (m)
B6
38.8
37.6
-1.2
38.0
-0.8
38.0
-0.8
E1
33.5
33.4
-0.1
33.0
-0.5
33.0
-0.5
D4
29.5
29.2
-0.3
28.8
-0.7
28.2
-1.3
B5
28.9
25
-3.9
26.5
-2.4
24.2
-4.7
C4
1
27.3
21.3
-6.0
22.8
-4.5
17.5
-9.8
C3
1
26.3
13.5
-12.8
20.0
-6.3
3.5
-22.8
D1
1
26.8
13.9
-12.9
20.6
-6.2
5.2
-21.6
1
26.00
21.2
-4.8
19.50
-6.5
16.50
-9.5
26.6
17.5
-9.1
20.7
-5.9
10.7
-15.9
B8
Average
Hydraulic
Head in
Southern
Block
Figure
Fig. 6-4
Fig. 7-8
Fig. 7-9
Fig. 7-10
Note: The highlighted piezometers are installed in the drift within the southern block of the Spur; -∆H is the change between the calculated head
1-
2
3
compared to the existing (i.e. U/S water level of El. 17.5m); - The duration of the pumping is assumed 1 year for the case study
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7.2.6
Reservoir at El. 25m – Impact of Cut-off Wall, Till Blanket, Finger Drains and Pump Well
System
Table 7-9 summarizes predicted piezometric levels in the upper drift deposits corresponding
to U/S water level of El. 25m and D/S water level of El. 3 m. These analyses were undertaken
to study the impact of the cut-off wall, till blanket, finger drains and pumped well system.
•
Referring to Table 7-9, at the Stage 1 U/S water level (El. 25 m), the average head in the
south block of the Spur increases to about El. 27.9m (i.e. an increase of about 1.3 m).
Taking into account all piezometers, the corresponding rising is about 1.0 m comparing to
the existing condition ‘Do Nothing’ case. Figure 7-11 shows the calculated hydraulic head
contours.
•
After installation of the U/S cut-off wall, the piezometric levels drop. The average head in
the south block of the Spur drops to about El. 26.0m (i.e. a drop of about 0.6 m). Taking
into account all piezometers, the corresponding drop is about 0.2 m comparing to the
existing condition ‘Do Nothing’ case. Figure 7-12 shows the calculated hydraulic head
contours.
•
Construction of the cut-off wall and till blanket but without finger drains and pumping
resulted in an average head in south block of the Spur increase to about El. 28.5 m (i.e.
an increase of about 1.9 m). Taking into account all piezometers, the corresponding head
increase in the Spur is about 1.4 m compared to the existing conditions. This occurs
because the U/S blanket impedes drainage toward the U/S slope. Figure 7-13 shows the
calculated hydraulic head contours.
•
Analyses with the cut-off wall, till blanket and finger drains implemented but no pumping
shows that the average head in the southern block of the Spur decreases to about El.
22.1m corresponding to about 4.6 m drop. Taking into account all piezometers, the
corresponding head drop in the Spur is about 2.7m compared to the existing conditions.
Figure 7-14 shows the calculated hydraulic head contours.
•
The calculated piezometric levels in the Spur decrease by an average 14.6 m in the
southern block and about 8.0 m drop in the entire Spur compared to existing conditions
assuming the cut-off wall, blankets and finger drains are installed and the pump well
system is operated in accordance with the existing pump rates. Figure 7-15 shows the
calculated hydraulic head contours.
Figure 7-16 shows the calculated hydraulic head profile in IA before and after construction of
stabilization works corresponding to U/S water level of El.25 m (the pumping system is off).
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Table 7-9: Summary of Calculated Piezometric Response at U/S WL=El. 25m with Installation of Stabilization Elements and Operation of Pump Wells
U/S WL at
El. 17.5 m
Piezometer
Hydraulic Head
Before Stabilization
(IA-0-a)
Hydraulic Head (m) @ U/S WL= El.25 m
Before Stabilization
(IA-1)
Hydraulic
Head (m)
∆H (m)
2
COW+
Blankets
(IA-3)
COW
(IA-2)
Hydraulic
Head (m)
B6
38.8
39.8
1.0
40.20
E1
33.5
34.10
0.6
D4
29.5
29.80
0.3
∆H (m)
2
Hydraulic
Head (m)
COW+
Blankets+
Drains+ Pumps
3
(IA-5)
COW+
Blankets+
Drains(IA-4)
∆H (m)
2
Hydraulic
Head (m)
∆H
2
(m)
Hydraulic
Head (m)
∆H (m) 2
-0.4
38.30
-0.5
1.4
39.50
0.7
38.40
35.00
1.5
35.00
1.5
34.00
0.5
34.00
0.5
29.10
-0.4
29.80
0.3
28.60
-0.9
28.10
-1.4
B5
28.9
29.50
0.6
27.50
-1.4
29.80
0.9
26.50
-2.4
24.50
-4.4
C41
27.3
28.60
1.3
26.50
-0.8
30.00
2.7
23.80
-3.5
18.90
-8.4
C31
26.3
27.60
1.3
25.90
-0.4
29.30
3.0
21.40
-4.9
6.70
-19.6
1
D1
26.8
28.10
1.3
26.10
-0.7
29.20
2.4
21.90
-4.9
4.10
-22.7
B81
26.0
27.30
1.3
25.40
-0.6
25.60
-0.4
21.10
-4.9
18.50
-7.5
Average Hydraulic
Head
in Southern Block
26.6
27.9
1.3
26.0
-0.6
28.5
1.9
22.1
-4.6
12.1
-14.6
Figure
Fig. 6-4
Fig. 7-11
Fig. 7-12
Fig. 7-13
Fig. 7-14
Fig. 7-15
Note: The highlighted piezometers (C4, C3, D1 and B8) are installed in the drift within the southern block of the Spur; ∆H is the change between the
1-
2
3
calculated head compared to the existing conditions (i.e. U/S water level of El. 17.5m); The duration of the pumping is assumed 1 year for the case
study
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7.2.7
Reservoir at El. 39m – Impact of Cut-off Wall, Till Blanket, Finger Drains and Pump Well
System
Table 7-10 summarizes predicted piezometric levels in the upper drift deposits corresponding
to U/S water level of El. 39m and D/S water level of El. 3 m. These analyses were undertaken
to study the impact of the COW, till blanket, finger drains and pumped well system.
•
Referring to Table 7-10, at the Stage 2 U/S water level (El. 39 m), the average head in
the south block of the Spur increases to about El. 36.4m (i.e. an increase of about 9.8 m).
Taking into account all piezometers, the corresponding rising is about 6.7 m comparing to
the existing condition ‘Do Nothing’ case. Figure 7-17 shows the calculated hydraulic head
contours.
•
After installation of the U/S cut-off wall, the average head in the south block of the Spur is
about El. 30.9 m (i.e. an increase of about 4.3 m). Taking into account all piezometers,
the corresponding increase is about 3.2 m comparing to the existing condition or ‘Do
Nothing’ case. Figure 7-18 shows the calculated hydraulic head contours.
•
Construction of the cut-off wall and till blanket but without finger drains and pumping
resulted in an average head in south block of the Spur increase to about El. 36.0m (i.e.
an increase of about 9.4 m). Taking into account all piezometers, the corresponding head
increase in the Spur is about 6.6 m compared to the existing conditions. This occurs
because the U/S blanket impedes drainage toward the U/S slope. Figure 7-19 shows the
calculated hydraulic head contours.
•
Analyses with the cut-off wall, till blanket and finger drains implemented but no pumping
shows that the average head in the southern block of the Spur decreases to about El. 23
m corresponding to about 3.6 m drop. Taking into account all piezometers, the
corresponding head drop in the Spur is about 1.5 m compared to the existing conditions.
Figure 7-20 shows the calculated hydraulic head contours.
•
The calculated piezometric levels in the Spur decrease by an average 15.3 m in the
southern block and about 7.7 m drop in the entire Spur compared to existing conditions
assuming the cut-off wall, blankets and finger drains are installed and the pump well
system is operated in accordance with the existing pump rates. Figure 7-21 shows the
calculated hydraulic head contours.
Figure 7-22 shows the calculated hydraulic head profile in the IA before and after construction
of stabilization works corresponding to U/S water level of El.39 m (the pumping system is off).
7.2.8
Impact of Penetration Depth in Lower Clay for Cut-off Wall
Sensitivity analyses were carried out to investigate the impact of the penetration depth of cutoff wall into the lower clay on the hydraulic heads in the IA. The penetration depths of 2 m, 5
m and 10 m were performed in the study. The results indicated that there was almost no
change in the piezometric readings of the IA with changing the penetration depth. It will be
important to ensure the cut-off wall penetrates below sand layers and lenses in the clay
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deposit if they exist at the IA-Marine Clay interface. Such interfaces tend to be transitional in
nature.
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Table 7-10: Summary of Calculated Piezometric Response at U/S WL = El.39 m with Installation of Stabilization Elements and Operation of
Pump Wells
U/S WL at
El. 17.5 m
Piezometer
Hydraulic
Head Before
Stabilization
(IA-0-a)
Hydraulic Head (m) @ U/S WL= El.39 m
Before
Stabilization
(IA-6)
COW+
Blankets
(IA-8)
COW
(IA-7)
COW+
Blankets+
Drains(IA-9)
COW+
Blankets+
Drains+ Pumps
3
(IA-10)
Hydraulic
Head (m)
∆H
2
(m)
Hydraulic
Head (m)
∆H
2
(m)
Hydraulic
Head (m)
∆H
2
(m)
Hydraulic
Head (m)
∆H
2
(m)
Hydraulic
Head (m)
∆H
2
(m)
B6
38.8
43.9
5.1
42.1
3.3
45
6.2
41.2
2.4
41.2
2.4
E1
33.5
36.3
2.8
36
2.5
37
3.5
35.1
1.6
35.1
1.6
D4
29.5
31.2
1.7
30.4
0.9
31
1.5
29.2
-0.3
28.7
-0.8
B5
28.9
33.8
4.9
30.6
1.7
33
4.1
27.3
-1.6
25.1
-3.8
C4
1
27.3
37.4
10.1
31.4
4.1
36.9
9.6
25
-2.3
20.3
-7
C3
1
26.3
36.9
10.6
30.9
4.6
36.6
10.3
22.7
-3.6
1.5
-24.8
D1
1
26.8
36.3
9.5
30.6
3.8
35.7
8.9
22.8
-4
4.2
-22.6
B8
1
26.0
35.1
9.1
30.7
4.7
34.6
8.6
21.6
-4.4
19.3
-6.7
Average
Hydraulic
Head in
Southern
Block
26.6
36.4
9.8
30.9
4.3
36.0
9.4
23.0
-3.6
11.3
-15.3
Figure
Fig. 6-4
Fig. 7-17
Fig. 7-18
Fig. 7-19
Fig. 7-20
Fig. 7-21
Note: The highlighted piezometers (C4, C3, D1 and B8) are installed in the drift within the southern block of the Spur; ∆H is the change between the calculated head
1-
2
3
compared to the existing (i.e. U/S water level of El. 17.5m); - The duration of the pumping is assumed 1 year for the case study
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7.2.9
Impact of Reservoir Impoundment on Kettle Lakes
The modeled response of the water levels in the kettle lakes accounting for the stabilization
works are summarized in Tables 7-11 and 7-12 for reservoir levels of El. 25 m and El. 39 m,
respectively. The following summarizes the results.
U/S Reservoir at El. 25 m
•
Referring to Table 7-11, without the stabilization works and with the pump wells off (i.e.
Do Nothing), the upper lake and lower levels were about El. 39 m and El. 29.8 m
respectively.
•
After installation of the U/S Cut-off wall only, there is no or insignificant change in the lake
levels compared to the Do Nothing case. The upper lake and lower levels were about El.
39 m and El. 29m respectively.
•
With installation of the U/S Cut-off wall and till blanket only (i.e. no D/S finger drains and
no pumping), the lake levels drop to El. 37.9m and El. 28.9 m for the upper and lower
lakes, respectively.
•
With the entire stabilization works installed and the pumping system off, the lake levels
drop to El. 37.4m and El. 28.5 m for the upper and lower lakes, respectively.
•
With the entire stabilization works installed and the pumping system operating according
to the current pump rates, there is a further modest drop in the lake levels. The
calculated lake levels are about El. 37.3m and El. 28 m for the upper and lower lakes,
respectively.
U/S Reservoir at El. 39 m
•
Referring to Table 7-12, without stabilization works and the pump wells are off (i.e. Do
Nothing), the upper lake and lower levels were about El. 39.5 m and El. 31.5 m
respectively.
•
After installation of the U/S Cut-off wall only, there is an insignificant change in the lake
levels compared to the Do Nothing case. The upper and lower lake levels were about El.
39.5 m and El. 31.2 m respectively.
•
With installation of the U/S Cut-off wall and till blanket (i.e. no D/S finger drains and no
pumping), the lake levels drop to El. 38.9 m and El. 30.5m for the upper and lower lakes,
respectively.
•
With the entire stabilization works installed and no pumping, the lake levels drop to El.
38.7m and El. 29.2 m for the upper and lower lakes, respectively.
•
There is a further modest drop in the lake levels with the entire stabilization works
installed and operating the current well system according to the current pump rates. The
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lake levels are at about El. 38.7 m and El. 28.8 m for the upper and lower lakes,
respectively.
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Table 7-11: Summary of Calculated Response for Kettle Lakes at U/S WL = El.25 m
Hydraulic Head (m) @ U/S WL= El. 25 m
Before
Stabilization
COW
COW+Blankets
COW+Blankets+Drains
COW+
Blankets+Drains+Pumps
Upper Lake
39
39
37.9
37.4
37.3
Lower Lake
29.8
29
29.9
28.5
28
Table 7-12: Summary of Calculated Response for Kettle Lakes at U/S WL = El.39 m
Hydraulic Head (m) @ U/S WL= El. 39 m
Before
Stabilization
COW
COW+Blankets
COW+Blankets+Drains
COW+
Blankets+Drains+Pumps
Upper Lake
39.5
39.5
38.9
38.7
38.7
Lower Lake
31.5
31.2
30.5
29.2
28.8
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8.
Summary
Based on the results obtained from the 3D FEFLOW models for LA and IA, a summary of the
findings are provided below.
8.1
Lower Aquifer
•
There is significant regional groundwater flow entering the site or model domain from the
north and west directions (see the dashed lines in Figure 1-2). These inflows have a
strong effect on the piezometric levels in the LA and they have been estimated as part of
the model calibration exercise. Based on the calibration, it is estimated that about 5 times
more groundwater enters the North Spur site from the west (i.e. flowing parallel to the
river) compared to the north. The groundwater inflow or flux from the west increases
approximately linearly with increasing reservoir levels. Approximate groundwater inflows
-2
3
2
-2
3
2
-2
3
2
or fluxes of 3 × 10 m /m /day, 4.6 × 10 m /m /day and 7.5 × 10 m /m /day were
estimated to enter the site from the west at U/S water level of El. 17.5m (existing
st
condition), El. 25m (the 1 stage reservoir rising) and El. 39m (the final reservoir rising),
respectively.
•
Without installation of the proposed ten D/S pressure relief wells (i.e. the ‘Do Nothing’
case), the FE model for the LA indicates that average piezometric heads will increase by
about 2.2 m compared to existing conditions when the U/S water level is raised to El. 25
m; there will be about 5.2 m increase in piezometric head during the final raise to
El. 39 m.
•
After installation of the proposed 10 D/S pressure relief wells, the FE results are identical
to the Do Nothing case indicating that the relief wells are expected to be ineffective for
the majority of the LA below the Spur for the reasons described in the next bullet point.
•
Piezometric levels (calculated) at the proposed pressure relief well locations in the LA will
rise from about El. 4.3 m corresponding to the existing conditions to El. 5.4 m and El. 6.9
m corresponding to U/S water levels of El. 25 m and El. 39 m, respectively. The
calculated piezometric levels are below the proposed outlet elevation at El. 7.0 m to El.
8.5 m corresponding to the ground surface. Provided the model assumptions are correct
and the lower aquifer is confined under a continuous thick layer of low permeability
marine clay, then relief wells should not be required for the lower aquifer. The pressure
relief wells will have no impact on piezometric levels in the North Spur after impoundment
unless a siphon system is employed or the outlet can be lowered below El. 4.0 m
(approximately).
•
Significant deviations from these results may indicate either leakage through the marine
clay somewhere upstream of the hydroelectric development, leakage into the lower
reservoir through fractured rock at the Muskrat Falls site, or that the marine clay layer has
limited lateral and U/S continuity.
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8.2
Upper Drift / Intermediate Aquifer Deposits
Existing Conditions
This section summarizes analyses results corresponding to an U/S water level of 17.5 m, and
D/S water level of 3m.
•
Without the pumped well system and finger drains, piezometric heads in the upper drift
deposits are high. The average head in the southern block of the Spur is about El. 26.6 m
corresponding to the existing condition.
•
With the operating the pump well system, the piezometric levels drop. The piezometric
levels in the Spur decrease by 5.3 m in average compared to existing conditions. The
average head in the south block of the Spur decreases by about 9.1 m. As such, the
existing pump well system has a significant impact on lowering the piezometric levels in
the southern block of the Spur, which is considered as the most critical part of the North
Spur.
•
If the finger drains are installed and the existing pump well system is discontinued, the
piezometric levels in the Spur decrease by 3.5m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 5.9m.
Consequently, the finger drains are not as effective as the pumped well system.
•
If the finger drains are installed and the pump well system is operated according to
existing pump rates, the piezometric heads are estimated to decrease by 8.9 m on
average compared to existing conditions. The average head in the south block of the
Spur decreases by about 15.9m.
As such, the operation of the existing dewatering system caused a relatively larger drawdown
in south block but less impact on the rest of the Spur; The D/S finger drains have a significant
impact on lowering the piezometric levels in the southern block of the Spur but the impact is
less than the pumped well system. Operating both the pumped well system and installing the
finger drains has the biggest impact on the Spur piezometric levels.
First Stage Reservoir Impoundment (El. 25 m)
This section summarizes analyses undertaken for the U/S water level of 25m and a D/S water
level of 3 m.
•
Without stabilization works and assuming the existing pump well system is discontinued
(i.e. Do Nothing), the piezometric levels in the Spur increase by 1.0 m on average
compared to existing conditions. The average head in the south block of the Spur
increases by about 1.3 m.
•
With the cut-off wall only and no till blanket, finger drains, or pumped wells, the
piezometric levels in the Spur decrease by 0.2 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 0.6 m.
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•
With construction of the cut-off wall and till blanket but without finger drains and pumping,
the piezometric levels in the Spur increase by 1.4 m average compared to existing
conditions. The average head in the south block of the Spur increases by about 1.9m.
This occurs because the U/S blanket impedes drainage toward the U/S slope.
•
With construction of the cut-off wall, till blanket and finger drains implemented but no
pumping, the piezometric levels in the Spur decrease by 2.7 m in average compared to
existing conditions. The average head in the south block of the Spur decreases by about
4.6m.
•
With construction of the entire stabilization works and operation of the pump wells, the
piezometric levels in the Spur decrease by 8.0 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 14.6m.
Final Stage Reservoir Impoundment (El. 39 m)
This section summarizes analyses undertaken for the U/S water level of 39m and a D/S water
level of 3 m.
•
Without stabilization works and if the existing pump well system is discontinued (i.e. Do
Nothing), the piezometric levels in the Spur increase by 6.7 m on average compared to
existing conditions. The average head in the south block of the Spur increases by about
9.8 m.
•
With the cut-off wall only and no till blanket, finger drains, or pumped wells, the
piezometric levels in the Spur increase by 3.2 m on average compared to existing
conditions. The average head in the south block of the Spur increases by about 4.3 m.
•
With construction of the cut-off wall and till blanket but without finger drains and pumping,
the piezometric levels in the Spur increase by 6.6 m on average compared to existing
conditions. The average head in the south block of the Spur increases by about 9.4m.
This occurs because the U/S blanket impedes drainage toward the U/S slope.
•
With the cut-off wall, till blanket and finger drains implemented but no pumping, the
piezometric levels in the Spur decrease by 1.5 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 3.6m.
•
With construction of the entire stabilization works and operation of the pump wells, the
piezometric levels in the Spur decrease by 7.7 m on average compared to existing
conditions. The average head in the south block of the Spur decreases by about 15.3 m.
Impact of Penetration Depth in Lower Clay for Cut-off Wall
•
The FE results of sensitivity analyses indicated that penetration depth of the cut-off wall
in the lower clay has negligible impact on the piezometric heads in the intermediate
aquifer drift deposits.
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Impact on the Kettle Lakes
The following lake levels are predicted corresponding to the impact of the stabilization
measures and the existing pump well system with various reservoir levels
a) U/S Reservoir at El. 25 m
•
With no stabilization works and the pump wells are off (i.e. Do Nothing), the upper lake
and lower levels were about El. 39 m and El. 29.8 m respectively.
•
With construction of U/S Cut-off wall only (i.e. no till blanket, pumping and D/S finger
drains), the lake levels changed slightly compared to the Do Nothing case. The upper
lake and lower levels were about El. 39 m and El. 29m respectively.
•
With construction of U/S Cut-off wall and till blanket (no D/S finger drains and operation
of pump wells), lake levels drop to El. 37.9 m and El. 28.9 m for the upper and lower
lakes, respectively.
•
With construction of the entire stabilization works and the pumping system is off, the lake
levels drop to El. 37.4m and El. 28.5 m for the upper and lower lakes, respectively.
•
If the entire stabilization works are implemented and the pumping system operated
according to the current pump rates, the lake levels are at about El. 37.3 m and El. 28 m
the upper and lower lakes, respectively.
b) U/S Reservoir at El. 39 m
•
With no stabilization works or pumping (i.e. Do Nothing), the upper lake and lower levels
were about El. 39.5 m and El. 31.5 m respectively.
•
With construction of U/S Cut-off wall only (i.e. no till blanket, pumping and D/S finger
drains), the lake levels change slightly compared to the Do Nothing case. The upper and
lower lake levels were about El. 39.5 m and El. 31.2 m respectively.
•
With construction of the U/S Cut-off wall and till blanket (no D/S finger drains and
operation of pump wells), lake levels drop to El. 38.9 m and El. 30.5m for the upper and
lower lakes, respectively.
•
With construction of the entire stabilization works and the pumping system is off, the lake
levels drop to El. 38.7m and El. 29.2 m for the upper and lower lakes, respectively.
•
If the entire stabilization works are implemented and the pumping system operated
according to the current pump rates, the lake levels are at about El. 38.7 m and El. 28.8
the upper and lower lakes, respectively.
The following tables summarize the change in piezometric levels in the upper drift deposits
(IA) relative to the Existing Conditions (i.e. the current geometry without the pumped well
system in operation).
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Table 8-1: Summary with Reservoir at El. 17.5m
Location
Existing
Condition
El. 29.6 m
El. 26.6 m
Average All Piezometers
Average South Block only
With
Pumping
-5.3 m
-9.1 m
With Finger
Drains
-3.5 m
-5.9 m
Both
-8.9
-15.9
Table 8-2: Summary with Reservoir at El. 25m
Location
Average All Piezometers
Average South Block only
Do
Nothing
CoW
Only
CoW and
Blanket
+1.0 m
+1.3 m
-0.2 m
-0.6 m
+1.4 m
+1.9 m
CoW,
Blanket &
Drains
-2.7 m
-4.6 m
All
-8.0 m
-14.6 m
Table 8-3: Summary with Reservoir at El. 39 m
Location
Average All Piezometers
Average South Block only
8.3
Do
Nothing
CoW
Only
CoW and
Blanket
+6.7 m
+9.8 m
+3.2 m
+4.3 m
+6.6 m
+9.4 m
CoW,
Blanket &
Drains
-1.5 m
-3.6 m
All
-7.7 m
-15.3 m
Future Considerations
•
Based on the findings from this study updating of the 3D FEFLOW model should be
considered during construction of the project.
H346252-0000-00-124-0001, Rev. 0,
Page 45
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Nalcor Energy
Hydrogeological Model of North Spur
H346252
Figures
H346252-0000-00-124-0001, Rev. 0,
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Figure 1-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Site Location Plan
Kettle Lakes
North Bank
North Bank
U/S
North Spur
Churchill River
Upstream (U/S)
Churchill River
Downstream (D/S)
Rock Knoll
South Bank
Location of Muskrat Falls
Dam
South Bank
Figure 1-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Aerial Photograph of the Site (Google Earth, 2014)
Landslides
Study Area
U/S
Rock Knoll
D/S
Muskrat Falls Hydropower
Station
Figure 1-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Ground Topography and River Bathymetry Based on LiDAR
Figure 3-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Conductivity Versus Depth in Bedrock Based on Packer Testing in 1979
Figure 3-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Layout of the Dewatering Pumpwells Installed in 1981
Figure 3-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Location of Lower Aquifer Wells and Piezometers
North Spur
U/S
Rock Knoll
D/S
Figure 5-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
3D DXF Geological Model (Converted from Catia Data)
Upper Silty Clay
Lower Silty Clay
Upper Sand
Upper Silty Sand (Drift -Zone A)
Lower Silty Sand (Drift- Zone B)
Lower Clay
Figure 5-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Cross Section through Converted Catia Model
U/S
U/S
D/S
D/S
Figure 5-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
3D Finite Element Mesh – Lower Aquifer
Kettle Lakes
1.5 Km
U/S
D/S Knoll
Rock
D/S
D/S Scour Hole
1.65 Km
Figure 5-4
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
3D Finite Element Mesh – Upper Drift Deposits (IA)
Model U/S
Total Head, 17.5m
U/S
Surface of
Lower Clay
Total Head, 3.0m
Model D/S
Figure 5-5
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions of 3D FEFLOW Model for LA
D/S
Side of Model
No Flow
U/S
Inflow Flux from North
(Q2)
Inflow Flux from West
(Q1)
Figure 5-6
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions of 3D FEFLOW Model for LA-Cont’d
Top Surface of
Lower Clay
U/S
Side of Model
No Flow Boundary
D/S
Bedrock Surface
No Flow Boundary
Figure 5-7
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions of 3D FEFLOW Model for LA-Cont’d
4.00E-05
3.50E-05
Unit Flux Q (m3/s)
3.00E-05
2.50E-05
2.00E-05
1.50E-05
1.00E-05
Q of LA-U/S 500m Away from North Spur
5.00E-06
0.00E+00
0
5
10
15
20
25
Upstream WL el. (m)
30
35
40
Figure 5-8
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Modeled Inflow from West to LA Versus Reservoir Heads
(Developed from 2D FE Analysis)
45
Kettle Lake
Region
Rock
Knoll
Low Permeable Material
Blocking D/S Scarps
Model D/S
Figure 5-9
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Impervious Slope Debris Covering the D/S Failure Scarps
White Faces: Seepage
Faces (SF)
SF
North Spur
SF
SF
U/S
U/S River:
Total Head = 17.5 m
D/S River:
Total Head = 3 m
Model Side (Knoll):
No Flow
Figure 5-10
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions for IA 3D FEFLOW Model
Infiltration Rate
1.2×10-9 m/s
Rock Knoll
D/S Riverbed
Infiltration
U/S
Riverbed
Infiltration
Infiltration
Regional Inflows, Flux
D/S
(QW)
Regional Inflows, Flux
(QN)
Figure 5-11
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions for IA 3D FEFLOW Model-Cont’d
1.80E-06
1.60E-06
Unit Flux Q (m3/s)
1.40E-06
1.20E-06
1.00E-06
8.00E-07
6.00E-07
Q of IA-U/S 1000m Away from North Spur
4.00E-07
2.00E-07
0.00E+00
0
10
20
30
Upstream WL el. (m)
40
Figure 5-12
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Relationship Between the N-W flux and Upstream Reservoir Levels for IA
(Developed from 2D FE Seepage Analyses)
50
Figure 6-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in the LA - Initial Conditions ( @U/S WL=El.17.5 m)
In-situ Measurement
3D FEFLOW Model
Figure 6-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in the LA during Pumping Test
Pump Well F2
installed in LA
Figure 6-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Pump Well F2 Installed in the LA 3D Model
Figure 6-4
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Piezometric Contours for the Upper Drift Deposits - Initial Conditions
Figure 6-5
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours for Short Term Pumping Test from FEFLOW Modeling
Figure 6-6
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours after 13 Months Pumping Test from FEFLOW Modeling
Figure 6-7
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours after 27 Months Pumping Test from FEFLOW Modeling
10 Relief Wells ( A-J) installed in LA
with minimum depth of 5m
U/S
J
A
D/S
Figure 7-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Pressure Relief Wells A to J in the 3D FEFLOW Model of LA
Figure 7-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of LA at @ U/S WL=El.25 m
Figure 7-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of LA at @ U/S WL=El.39 m
U/S Till Blanket (k=1x10-8 m/s)
Cut-off Wall
Cross Section
Figure 7-4
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
U/S Cut-off Wall and Till Blanket in the 3D FEFLOW Model
Proposed D/S
Finger Drains with
K of 1 x 10-3m/s
Figure 7-5
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
D/S Finger Drains in 3D FEFLOW Model
Figure 7-6
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL=El.25 m before Stabilization (IA-1)
Figure 7-7
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL=El.39 m before Stabilization (IA-6)
Figure 7-8
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in the IA at U/S WL=El.17.5m with Pump Well System (IA-0-b)
Figure 7-9
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL=El.17.5m with D/S Finger Drain (IA-0-c)
Figure 7-10
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL=El.17.5m with D/S Finger Drain and Pumping (IA-0-c)
Figure 7-11
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL=El.25 m before Stabilization (IA-1)
Figure 7-12
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL=El.25 m after Installation of COWs ( IA-2)
Figure 7-13
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours of IA at U/S WL= El. 25 m after Installation of COWs + Blankets (IA-3)
Figure 7-14
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head contours in IA at U/S WL= El. 25 m with COWs+ Blankets+ Finger Drains ( IA-4)
Figure 7-15
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL=El. 25 with of COWs+ Blankets+ Finger Drains+
Pump Wells System ( IA-5)
Before Stabilization
After Stabilization (COWs+ Blankets+ Finger Drains)
35
Hydraulic Head (m)
30
25
20
15
10
5
0
0
100
200
300
400
500
600
700
Distance (m)
Figure 7-16
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Calculated Hydraulic Head Profile in IA at U/S WL= El.25 m after Installation
of Stabilization Works
800
Figure 7-17
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL= El.39m before Stabilization ( IA-6)
Figure 7-18
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL= El.39m after Installation of COWs (IA-7)
Figure 7-19
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL= El.39 m with COWs + Blankets (IA-8)
Figure 7-20
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head Contours in IA at U/S WL= El.39 m with COWs+ Blankets+ Finger Drains ( IA-9)
Figure 7-21
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Hydraulic Head contours in IA at U/S WL= El.39m with COWs+ Blankets+ Finger Drains+
Pump Wells System (IA-10)
Before Stabilization
After Stabilization (COWs+ Blankets+ Finger Drains)
45
Hydraulic Head (m)
40
35
30
25
20
15
10
5
0
0
100
200
300
400
500
600
700
Distance (m)
Figure 7-22
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Calculated Hydraulic Head Profile in IA at U/S WL= El.39m after Installation
of Stabilization Works
800
Nalcor Energy
Hydrogeological Model of North Spur
H346252
Appendix A
Modeling Basis for 3D Hydrogeological
Study of the North Spur
H346252-0000-00-124-0001, Rev. 0,
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Project Memo
H346252
To:
Bob Ilett
CC:
Regis Bouchard – SLI
Tony Chislett – Hatch
Richard Donnelly – Hatch
Sean Hinchberger-Hatch
Warren Hoyle-Hatch
Ali El-Takch – Hatch
David Parkes – Hatch
From:
George Liang
March 20, 2014
Nalcor Energy
Lower Churchill Project
Modelling Basis for 3D Hydrogeological Study of the North Spur
1.
Introduction
Hatch has been retained by Nalcor Energy (Nalcor) to undertake a three dimensional (3D)
hydrogeological study for the North Spur of the Muskrat Falls hydroelectric project in
Labrador. The study was started on January 27, 2014. A Hatch geotechnical engineer visited
LCP St. John’s project office to collect the data for this study during the period of January 28
to 31, 2014. A review of this data was conducted following the site visit. This memorandum
summarizes the modelling basis for this study.
2.
Data Collection
The following background information/data were obtained from SNC Lavalin Inc. (SLI) during
the site visit:
•
Muskrat Falls Development. A report to the British Newfoundland Corporation Limited.
October 1965, Acres Canadian Bechtel.
•
Lower Churchill Consultants. Muskrat Falls Development. Geotechnical Review of 1965
layout. A report to the Gull Island Power Company Limited. June 1976.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. I: Engineering report, 1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. II: Appendices, 1980, SNC-Lavalin Newfoundland Ltd.
H346252-0000-00-219-0001, Rev. 0
Page 1
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. III: 1979 Field exploration program-soils investigation-borehole logs & lab results,
1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Power Development and 345 kV Transmission Intertie to Churchill Falls,
Vol. IV: 1979 Field exploration program-construction materials-test pits & trenches-logs &
lab results, 1980, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Dewatering System, Construction Report, Operation and Maintenance
Information, March 1982, Report No. 11.99.18, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Dewatering System, Engineering Assessment, March 1982, Report No.
11.99.18, SNC-Lavalin Newfoundland Ltd.
•
Muskrat Falls Hydroelectric project, Dewatering System Assessment and Rehabilitation,
Feb. 1997, Report No. P11759.01, Acres International Limited.
•
Muskrat Falls, Standpipe Piezometer Installation Program Report, Feb. 1998, Report No.
P11759.02, Acres International Limited.
•
Muskrat Falls Hydroelectric Development, Final Feasibility Study, Vol. 1, Engineering
report, Jan. 1999.
•
Muskrat Falls Hydroelectric Development, Final Feasibility Study, Vol. 2, 1998
Geotechnical Investigations, Jan. 1999.
•
The Lower Churchill Project, MF 1260- Assessment of Existing Pumpwell System- July
2008.
•
The Lower Churchill Project, MF 1271- Evaluation of Existing Wells, Pumps and Related
Infrastructure in the Muskrat Falls Pumpwell System, March 2010.
•
The Lower Churchill Project, MF 1272- Installation of New Piezometers in the Muskrat
Falls Pumpwell System, April 2010.
•
Muskrat Falls Geological Report, Part III, Photos for cores and site areas, 1979, LCP
Admin Rec. No. 202-120142-00019.
•
Geotechnical Investigations Report. 2013 Field Investigations- North Spur. Muskrat Falls
Hydroelectric Development. Lower Churchill Project. November 2013.
•
The Lower Churchill Project, Muskrat Falls, North Spur Stabilization Design Drawings,
Sept. 2012, SNC-Lavalin Newfoundland Ltd.
•
MF North Spur Layers, Catia -3D Geological Model, SNC-Lavalin Newfoundland Ltd.
•
Engineering Report-North Spur Stabilization (Draft) and related plates, SNC-Lavalin
Newfoundland Ltd, Dec. 2013;
•
Topographic Lidar data;
•
Aerial photographs: 1951, 1975 and 1988;
•
North Spur Stabilization Works Poster-Landslide in Sensitive Clay;
H346252-0000-00-219-0001, Rev. 0
Page 2
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
3.
3.1
3.2
3.3
•
PPT-North Spur-Advisory Board (02-Oct-2013);
•
PPT-North Spur Stabilization Works –Geology (23-Oct-2013);
•
Piezometer and pump-wells water level readings (working excel files to date), SNCLavalin Newfoundland Ltd.
Modelling Plan
Proposed Model Area for the North Spur
•
South Limit: Extends to bedrock knoll;
•
North Limit: Approximately 100 m north of three kettle lakes and the drainage valley;
•
West Limit: Approximately 300 m west of the proposed North-West upstream (U/S) cutoff walls (the existing U/S Churchill River water level is at approximately el. 17.5 m);
•
East Limit: Extends to downstream (D/S) of the Churchill River to the location where it is
assumed to connect with the Lower Aquifer (D/S water level is at approximately el. 3 m);
•
Site Stratigraphy: Extends to the bedrock surface (an impermeable bedrock is
assumed).
Stabilization Design Works Related to this Study
•
U/S cut-off Wall (COW) system, which penetrates 2 m into the lower clay (base case);
•
U/S Till blanket;
•
Existing pump well dewatering system installed in 1981;
•
D/S pressure relief wells (base case: 10 relief wells extending to the lower aquifer based
on the design);
•
D/S finger drain system.
Model Case Studies
Based on data review, during the 1979 pump test in the lower aquifer, the piezometric levels
in the intermediate aquifer did not change, which confirms there is no connection between the
two aquifers and the lower marine clay layer acts as an aquitard. Therefore, two separate
models will be setup for the Lower Aquifer (LA) and the Intermediate Aquifer(IA),
respectively.
3.3.1
Existing Conditions - Before Stabilization Construction
3D Model for IA:
•
Case 1-before installation of pump well dewatering system in 1981; U/S water level
(WL)=17.5 m; D/S WL=3 m;
•
Case 2-after installation of pump well dewatering system in 1981; U/S WL=17.5 m; D/S
WL=3 m.
H346252-0000-00-219-0001, Rev. 0
Page 3
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
3D Model for LA:
3.3.2
•
Case 3-exisitng condition before 1979 pump testing in LA; U/S WL=17.5 m; D/S WL=3 m;
•
Case 4-after pump testing in LA in 1979; U/S WL=17.5 m; D/S WL=3 m.
Reservoir Storage Conditions - After Stabilization Construction
3D Model for IA:
•
Case 5-U/S WL=25 m; D/S WL=3 m with U/S COW and Till blanket, pump wells and D/S
finger drains (in 2016);
•
Case 6-U/S WL=25 m; D/S WL=3 m with U/S COW and Till blanket, D/S finger drains.
The pump well system will be stopped (in 2016);
•
Case 7-U/S WL=39 m; D/S WL=3 m with U/S COW and Till blanket, D/S pump wells and
finger drains (in 2017);
•
Case 8-U/S WL=39 m; D/S WL=3 m with U/S COW, Till blanket and D/S finger drains (in
2017). The pump well dewatering system will be stopped.
3D Model for LA:
•
Case 9-U/S WL=25 m; D/S WL=3 m with D/S pressure relief well numbers 0, 5, 10 and
15 (in 2016);
•
Case 10-U/S WL=39 m; D/S WL=3 m with D/S relief well numbers 0, 5, 10 and 15 (in
2017).
Additional cases studies might be required considering various length of U/S North-West
COW.
3.4
Construction Considerations for North Spur Stabilization
•
The alignment of the U/S COWs is fixed. The penetration depth to the lower clay and
length of North-west Cut-off wall could be optimized if a sensitivity analysis is carried out
with this study.
•
The stabilization works (U/S and D/S) will be completed before an increase in reservoir
storage is developed.
GL:cdh
Attachment
Appendix A: 3D DXF Geological model converted by Catia
H346252-0000-00-219-0001, Rev. 0
Page 4
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Appendix A
3D DXF Geological Model Converted by
Catia
H346252-0000-00-219-0001, Rev. 0
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Nalcor Energy
Hydrogeological Model of North Spur
H346252
Appendix B
2D Seepage Analysis for Estimation of
Inflow Flux in Lower Aquifer and
Intermediate Aquifer of the North Spur
H346252-0000-00-124-0001, Rev. 0,
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table of Contents
1. Introduction ........................................................................................................................................... 3
2. Background ........................................................................................................................................... 3
2.1
2.2
Geological and Hydrogeological Setting ....................................................................................... 3
Typical Cross-Section for 2D Seepage Analysis .......................................................................... 4
2.2.1 2D Seepage Model for LA ................................................................................................... 4
2.2.2 2D Seepage Model for IA .................................................................................................... 4
3. Methodology ......................................................................................................................................... 5
3.1
Seepage Analysis ......................................................................................................................... 5
3.1.1 Hydraulic Conductivity......................................................................................................... 5
3.1.2 Boundary Conditions ........................................................................................................... 6
3.2 Estimated Quantity of Seepage Flux ............................................................................................ 6
4. Results ................................................................................................................................................... 7
4.1
Seepage Model Calibration .......................................................................................................... 7
4.1.1 Calibration for LA Model ..................................................................................................... 7
4.1.2 Calibration for IA Model ...................................................................................................... 7
4.2 Case Study ................................................................................................................................... 7
5. Summary ............................................................................................................................................... 8
6. References ............................................................................................................................................ 8
Page 2
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
1.
Introduction
Hatch was retained by Nalcor Energy (the Client) to perform three dimensional (3D) seepage
modeling for the North Spur of the Muskrat Falls hydroelectric project.
2
The model area for the North Spur is about 2.5 km , which is a limited in extent compared to
the regional geological and hydrogeological setting. Currently, upstream recharge to the
lower aquifer (LA) and intermediate aquifer (IA) are unknown; however, the regional recharge
rates should be estimated and entered as input for the 3D models.
The lower aquifer is generally confined, but recharge from the river, as leakage through the
overlying clay for a distance several kilometres upstream may be significant. The primary
source of recharge for the upper drift deposits is surface infiltration of precipitation.
To estimate recharge rates for the LA and IA, 2D seepage finite element (FE) analyses were
conducted using Geo-Studio 2012 package. The objective of the 2D seepage analysis was
to develop functions of inflow flux into the LA and IA versus the reservoir level, which will be
used to define boundary conditions for 3D FEFLOW model.
2.
Background
2.1
Geological and Hydrogeological Setting
Several investigation campaigns, pumping well installations and piezometer installations have
been performed on the North Spur since 1965. The most recent investigation program was
carried in 2013. The geological setting and hydrogeological conditions of the North Spur have
been addressed in the various geotechnical investigation reports.
Based on site investigation information, the geological settings of the North Spur from the
ground surface can be summarized as the following:
•
Upper sand (el. 60m to el.50m)
•
Stratified drift (el. 50m to el. 10 m)
•
Lower marine clay (el. 10 to el.-50 m)
•
Lower aquifer (el. -50 to Bedrock level-min. el.-210 m)
The existing hydrogeological condition consists of the presence of three aquifers:
•
An upper perched aquifer
•
Intermediate aquifer (IA) and
•
Lower aquifer (LA)
During the 1979 pumping tests in the LA, the piezometric levels in the IA did not change,
which confirmed there was no connection between the two aquifers and the lower marine clay
layer acts as an aquitard. Site investigation records in 1979 indicated that LA (in NS-2) is
connected with the downstream river water level.
Page 3
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2.2
Typical Cross-Section for 2D Seepage Analysis
2.2.1
2D Seepage Model for LA
Figure B-1 shows the location of the cross section of LA to develop 2D seepage model.
Figure B-3 illustrates the representative section used for the 2D FE seepage analysis with a
total model length of 15km along the river bed. Planner 2D vertical sections used in the 2D
seepage analysis are approximately along the centerline of the river. No regional
hydrogeological data are available to develop 2D seepage models with various orientations in
a horizontal plan. To facilitate the modeling, the layered drift materials in the North Spur were
simplified and the major soil layers were assumed to extend the full modeled distance
upstream.
The subsurface soils considered in the model for LA include:
a) The North Spur drift material (from El.60-El.10m);
b) Lower Clay (from El. 10m to El. -50m)
c) Lower Aquifer (sand and gravel/cobble, from El. -50m to El. -100m)
2.2.2
2D Seepage Model for IA
Figure B-2 shows the location of the cross section of IA to develop 2D seepage model. Figure
B-4 illustrates the representative section for the IA. This section was modeled using 2D FE
seepage analysis. The total model length is 5.5 km. The subsurface soils considered for the
IA model include:
a) The Upper Sand (from El.60-El.45m);
b) The North Spur drift material (from El.45-El.10m);
c) Lower Clay (from El. 10m to El. -50m)
Page 4
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3.
Methodology
3.1
Seepage Analysis
Steady state 2D FE seepage analyses were performed using commercial software GeoStudio (2012). Although the problem of the regional seepage for the site is actually threedimensional, 2D seepage analyses were used and considered satisfactory to develop the
boundary conditions for 3D FEFLOW models for both aquifers.
3.1.1
Hydraulic Conductivity
Table B-1 summarizes the hydraulic conductivities of the soil layers used for 2D FE Seepage
models.
Table B-1: Summary of Hydraulic Conductivity for Seepage Analysis
Permeability(m/s)
Soil Layer
Material
Kxx
Kyy
-4
1
2
Upper Sand
North Spur Drift Material
1.4×10
-5
5.86×10
3
4
Lower Clay
Lower Aquifer (Sand/Gravel/Cobble)
2×10
-4
1.4×10
-8
-4
1.4×10
-6
5.86×10
-8
2×10
-4
1.4×10
Page 5
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3.1.2
Boundary Conditions
3.1.2.1
Lower Aquifer
The boundary conditions for the LA model consist of:
•
A total head boundary is set up at the upstream surface of lower clay(river bed) and
North Spur. The total heads of 17.5m, 25m and 39m are assigned, respectively to
simulate the existing condition and two stages of reservoir raising;
•
A total head boundary of 3.0m is set up at the downstream side of the North Spur;
•
No flow boundaries at the left and at the bottom of the lower aquifer ( assuming the
bedrock is impermeable);
•
A potential seepage face boundary is applied on the downstream surface of the North
Spur above the water level.
Boundary conditions for the 2D seepage model are shown in Figure B-3
3.1.2.2
Upper Drift Deposits (Intermediate Aquifer)
Boundary conditions for the 2D IA model consist of:
-9
•
An infiltration rate of 1.2×10 m/s corresponding to 4% of the average annual precipitation
of 950mm/yr at the site was assigned on the top surface of the model;
•
A total head boundary is set up at the upstream end of the model North Spur. The total
head of 17.5m, 25m and 39m are assigned, respectively to simulate the existing
condition and two stages of reservoir raising.
•
A total head boundary of 3.0m is set up at the downstream end of the North Spur;
•
A no-flow boundary is set up at the bottom of the lower clay;
•
A potential seepage face boundary is applied on the downstream surface of the North
Spur above the water level.
The boundary conditions for the 2D seepage model is shown in Figure B-4
3.2
Estimated Quantity of Seepage Flux
For the LA 2D seepage model, two seepage flux sections were setup in the model (see
Figure B-3):
•
one flux section 500m upstream of the North Spur, where is the upstream boundary of 3D
FEFLOW model exists
•
a second flux section at downstream end.
The unit seepage fluxes passing through the sections were calculated for various reservoir
levels.
For the IA 2D seepage model, the following flux sections were setup in the model (See Figure
B-4) included:
Page 6
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•
One flux section in IA at 1000m North-West end of the North Spur, where the upstream
boundary of the 3D FEFLOW model exists
•
a second flux section in at the downstream surface.
Similarly, unit seepage fluxes passing through the sections were calculated for various
reservoir levels.
4.
Results
4.1
Seepage Model Calibration
4.1.1
Calibration for LA Model
The LA model was calibrated using the in-situ piezometer readings and estimated total flux in
the 1979 SLI investigation report.
For the existing conditions, the upstream water level is El. 17.5m and downstream water level
is 3 m. The calculated hydraulic head in the LA below the North Spur was in the range of 4-6
m with an average head of 5.0 m, which is comparable to about 5.4m average head reported
in the 1979 site investigations report.
3
In addition, a unit flux of 1.75m /s (unit width) was also obtained from seepage analysis for
LA at the downstream toe. This corresponds to a total flux of 17.5 l/s over the 1 km length of
LA at downstream side, which compares favourably to the estimated 18 l/s outflow from the
LA in the 1979 SLI investigation report (SNC-Lavalin Report, 1979).
Based on these results, the 2D seepage model is considered to be well calibrated. Figure B5 shows the contours of the hydraulic heads and unit flux under existing conditions.
4.1.2
Calibration for IA Model
The seepage model for IA was calibrated based on the in-situ piezometer measurements
installed in the spur. For the existing conditions corresponding to an upstream water level of
El. 17.5m and downstream water level of 3m, the calculated hydraulic head distribution (i.e.
the mounting groundwater table of the spur) in IA is comparable to the historic piezometeric
measurements in the spur. Figure B-9 shows calculated results for IA under existing
conditions.
4.2
Case Study
Tables B-2 and B-3 summarize the calculated results for the LA and IA corresponding to the
following U/S water levels::
•
reservoir at El. 25m;
•
reservoir at El. 32m; and
•
reservoir at El. 39m.
Figures B-6 to B-8 present the FE calculations for case study of LA; figures B-9 to B-11 show
results for the IA.
Figures B-12 and B-13 show the relationship between the reservoir water level and upstream
flux entering the 3D model domain in both the LA and IA, respectively.
Page 7
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From Figure B-12, it can be seen that an approximate liner relationship between inflow flux
and reservoir head was obtained in LA:
•
For the U/S flux section situated 500m from the North Spur, the unit inflow flux increased
-5 3
-5 3
from 1.47×10 m /s to 3.66×10 m /s corresponding to the reservoir level raising from El.
17.5m to 39m;
•
For the flux section at the D/S toe of the North Spur, the unit flux increased from
-5 3
-5 3
1.75×10 m /s to 4.34×10 m /s corresponding to the reservoir level raising from El. 17.5m
to 39m;
From Figure B-13, the similar trend was obtained:
•
For the U/S flux section situated 1000m from the North Spur, the unit inflow flux
-6 3
-6 3
increased from 1.26×10 m /s to 1.69×10 m /s corresponding to the reservoir level
raising from El. 17.5m to 39m;
•
For flux section at the D/S slope of the North Spur, the unit inflow flux increased from
-6 3
-6 3
1.93×10 m /s to 2.34×10 m /s corresponding to the reservoir level raising from El. 17.5m
to El.39m;
The flux values listed in Tables B-2 and B-3 should be utilized as input in 3D seepage models
of the site.
Table B-2:Seepage Flux Estimation in LA at Various Reservoir Levels
U/S WL
D/S WL
Unit Flux from U/S LA-500m away
3
from North Spur (m /s)
Figure
17.5
3
1.47E-05
B-5
25
3
2.24E-05
B-6
32
3
2.95E-05
B-7
39
3
3.66E-05
B-8
Table A-3:Seepage Flux Estimation in IA at Various Reservoir Levels
5.
U/S WL
D/S WL
Unit Flux from U/S IA-1000m away
3
from North Spur (m /s)
Figure
17.5
3
1.26E-06
B-9
25
3
1.35E-06
B-10
39
3
1.69E-06
B-11
References
1979 Field Exploration Program-Soil Investigation. Borehole logs & Lab Results. Volume I-III.
SNC-Lavalin Newfoundland Ltd. Plan et Profile 2011-07-14.dgn, Profiles A and B.
Page 8
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
A
A
Figure B-1: Location of Cross Section for LA
Page 9
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Figure B-2: Location of Cross Section for IA
Page 10
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Figure B-3: 2D Seepage Model for LA
Figure B-4: 2D Seepage Model for IA
Page 11
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Figure B-5: 2D Seepage Analysis for LA at WL of El.17.5m
Figure B-6: 2D Seepage Analysis for LA at WL of El. 25m
Page 12
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Figure B-7: 2D Seepage Analysis for LA at WL of El. 32m
Figure B-8: 2D Seepage Analysis for LA at WL of El. 39m
Page 13
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Figure B-9: 2D Seepage Analysis for IA at WL of El. 17.5m
Page 14
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Figure B-10: 2D Seepage Analysis for IA at WL of El. 25m
Page 15
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Figure B-11: 2D Seepage Analysis for IA at WL of El. 39m
Page 16
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4.00E-05
3.50E-05
Unit Flux Q (m3/s)
3.00E-05
2.50E-05
2.00E-05
1.50E-05
1.00E-05
Q of LA-U/S 500m Away from North Spur
5.00E-06
0.00E+00
0
5
10
15
20
25
Upstream WL El. (m)
30
35
40
45
Figure B-12: Unit flux in LA Versus Reservoir Head Based on 2D Seepage Analysis
1.80E-06
1.60E-06
Unit Flux Q (m3/s)
1.40E-06
1.20E-06
1.00E-06
8.00E-07
6.00E-07
Q of IA-U/S 1000m Away from North Spur
4.00E-07
2.00E-07
0.00E+00
0
5
10
15
20
25
30
35
40
45
Upstream WL El. (m)
Figure B-13: Unit flux in IA Drift Versus Reservoir Head Based on 2D Seepage Analysis
Page 17
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Nalcor Energy
Hydrogeological Model of North Spur
H346252
Appendix C
3D FEFLOW Sensitivity Analyses for Lower
Aquifer of the North Spur
H346252-0000-00-124-0001, Rev. 0,
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table of Contents
1. Sensitivity Analysis for LA .................................................................................................................. 3
2. Changing of Inflow Flux Ratio ............................................................................................................. 3
3. Changing of Hydraulic Conductivity .................................................................................................. 3
Page 2
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1.
Sensitivity Analysis for Lower Aquifer
The following sensitivity analyses have been preformed to investigate the impact of the main
factors on the piezometric response of LA:
2.
i)
Inflow flux ratio, Q1/Q2., where Q1 and Q2 are the inflow flux from the West and North
side of the study area, respectively;
ii)
Anisotropic features of the hydraulic conductivity.
Changing of Inflow Flux Ratio
Sensitivity analyses were performed to investigate the effect of inflow flux rates from the West
(Q1 from U/S) and North side (Q2) on the piezometric response of LA. Table C-1 summarizes
the calculated results of changing the flux ratio of Q1/Q2. Based on Table C-1, it can be seen
that:
3.
•
Inflow flux rates from both West and North direction in LA affect the piezometers reading.
Inflow flux Q1 from the west side (i.e. U/S of the North Spur) dominate the response of
the LA.
•
The calculated hydraulic heads at the specific locations of piezometers installed in the LA
increased with increasing the influx rates of Q1 and Q2.
•
The calculated results for influx ratio Q1/Q2 of 1/0.2 have a good match with the in-situ
measurement (Case S-1 in Table C-1). The error between the calculation and the
measurement is less than 1.8%. As a result, this flux ratio is determined for using of the
further model calibration.
Changing of Hydraulic Conductivity
Sensitivity analyses were also performed to investigate the anisotropic properties of the LA
materials on the hydraulic head in LA, which is for the case study of pumping tests in 1979.
Table C-2 summarized the results and the calculated drawdown values were compared with
the piezometer measurements.
From Table C-2, it can be seen that calculated drawdown values for S-7 are considered as
more reasonable comparing with the in-situ measurements. Therefore, the isotropic hydraulic
-4
conductivity of 1.4x10 m/s is used for further model calibration and case study.
Page 3
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Table C-1: Summary of the Sensitivity Analyses for Changing Influx Ratio of Q1/Q2
Piezometer No.
A1
F2
P1
D5
E1
B7
In-situ Piezometric Measurement in 1979 (m)
6.8
5.5
5.58
5.6
6
4.3
A1
F2
P1
D5
E1
B7
6.8
5.4
5.5
5.6
6.0
4.3
0.0%
-1.1%
-1.8%
0.0%
0.0%
-0.5%
6.6
5.4
5.4
5.5
5.8
4.2
-2.6%
-2.2%
-2.9%
-2.7%
-3.2%
-2.3%
7.2
5.8
5.9
5.9
6.4
4.5
5.6%
5.5%
5.0%
5.9%
7.0%
3.5%
5.9
5.0
5.1
5.1
5.5
4.1
-14.0%
-10.0%
-9.5%
-8.9%
-8.8%
-5.8%
6.4
5.3
5.3
5.4
5.8
4.2
-6.6%
-4.5%
-5.0%
-4.5%
-4.2%
-2.8%
5.4
4.7
4.8
4.8
5.2
4.0
-20.3%
-14.5%
-14.9%
-13.6%
-13.3%
-8.1%
Q1/Q2
West Flux
Q1 (m/s)
North Flux
Q2 (m/s)
S-1
1:0.2
3.00E-07
6.00E-08
S-2
1:0.05
3.00E-07
1.50E-08
S-3
1:0.5
3.00E-07
1.50E-07
S-4
0.6:0.6
1.80E-07
1.80E-07
S-5
0.8:0.4
2.40E-07
1.20E-07
S-6
0.4:0.8
1.20E-07
2.40E-07
Sensitivity
Analysis
1
3D FEFLOW
Model
Error
Error
Error
Error
Error
Error
Note:1- The highlighted case indicated that the calculated results were comparable with existing piezometers measurements.
Page 4
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Table C-2: Summary of the Sensitivity Analyses for Changing Hydraulic Conductivity of LA (1979 Pump Testing)
Piezometer No.
A1
F2
P1
D5
E1
B7
Measured drawdown during pump testing in 1979
1.9
20.4
7.19
2.16
1.84
2.1
Sensitivity
Analysis
1
Permeability for LA Material
(m/s)
Kx
Ky
Kz
S-7
1.40E-04
1.40E-04
1.40E-04
S-8
2.80E-04
1.40E-04
1.40E-04
S-9
1.40E-04
2.80E-04
1.40E-04
3D FEFLOW Model
Calculated Drawdown based on 3D FEFLOW Model (m)
A1
F2
P1
D5
E1
B7
3.6
14.5
7.38
2.8
1.8
1.8
89.5%
-28.9%
2.6%
29.6%
-2.2%
-14.3%
5.1
11.5
7.33
3.15
2.7
2.2
168.4%
-43.6%
1.9%
45.8%
46.7%
4.8%
2.9
10.5
5.48
2.8
2.25
1.5
52.6%
-48.5%
-23.8%
29.6%
22.3%
-28.6%
error
error
error
Note:1- The highlighted case indicated that the calculated results were comparable with the piezometers measurements.
Page 5
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Nalcor Energy
Hydrogeological Model of North Spur
H346252
Appendix D
3D FEFLOW Sensitivity Analyses for
Intermediate Aquifer of the North Spur
H346252-0000-00-124-0001, Rev. 0,
Ver: 04.00
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table of Contents
1. Sensitivity Analysis for 3D FEFLOW Modelling for IA ...................................................................... 3
2. Initial Geological Model of IA .............................................................................................................. 3
3. Hydraulic Conductivity ........................................................................................................................ 3
4. Initial Boundary Conditions for IA Model ........................................................................................... 4
5. Piezometeric Response under Initial Boundary Conditions ............................................................ 4
6. Calibration Scenarios (Sensitivity Studies) ....................................................................................... 5
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
Scenario 1-Sensitivity Study by Changing North-West Inflow Flux Rates .................................... 5
Scenario 2- Sensitivity Study by Changing Infiltration Rate ......................................................... 6
Scenario 3- Extending the INF Surface to Cover D/S Scarp Surface .......................................... 7
Scenario 4- Extending the INF Surface and Changing K of Drift Material Zone-B of
Southern block .............................................................................................................................. 7
Scenario 5- Extending the INF Surface Area and Introducing INF from Rock Knoll
Surface .......................................................................................................................................... 8
Scenario 6 - Increasing the INF Surface, Introducing Additional INF from Rock Knoll
Surface and Adjusting Permeability of Drift Materials .................................................................. 9
Scenario 7- Increasing the INF Surface, Introducing Additional INF from Rock Knoll
Surface and Increase Permeability for Silty Clay layers ............................................................. 10
Scenario 8 - Increasing the INF surface and Conducting Flux from Southern Fractured
Bedrock Surface ......................................................................................................................... 11
Scenario 9-Blockage of D/S Scarps Slope Surface.................................................................... 13
Page 2
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1.
Sensitivity Analysis for 3D FEFLOW Modelling for IA
A total number of nine (9) Scenarios with twenty four (24) case studies were conducted to
determine the best Scenario for IA FEFLOW model calibration and case study. The details
are summarized in the following sections.
2.
Initial Geological Model of IA
The initial geological settings are included six (6) soil layers in IA 3D FEFLOW model:
3.
•
Upper sand layer
•
Upper silty clay layer
•
Upper silty sand drift zone A
•
Lower silty clay layer
•
Lower silty sand drift zone B
•
Lower clay
Hydraulic Conductivity
Hydraulic conductivity values were estimated based on the site investigation information
assigned to the soil layers in the 3D FEFLOW model. Table D-1 summarizes the hydraulic
conductivities for the soil layers of IA used in this study.
Table D-1: Hydraulic Conductivities Used in FEFLOW Model for IA
No.
Soil Layers
Hydraulic Conductivity, K (m/s)
1
Upper Sand
Kxx=Kyy=Kzz= 1x10
-4
2
Upper Silty Clay
Kxx=Kyy=Kzz= 1x10
-7
3
Upper Silty Sand Drift -Zone A
Kxx=Kyy=Kzz= 8x10
-6
4
Lower Silty Clay
Kxx=Kyy=Kzz= 1x10
-7
5
Lower Silty Sand Drift -Zone B
Kxx=Kyy=Kzz= 8x10
-6
6
Lower Clay
Kxx=Kyy=Kzz= 1x10
-8
1
Note: 1- Hydraulic conductivity for the soil layers of IA were based on 1981 pumping tests results. Kxx, Kyy and Kzz are the
hydraulic conductivities in three directions in 3D FEFLOW model.
Page 3
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4.
Initial Boundary Conditions for IA Model
Table D-2 summarized the initial boundary conditions assigned for IA 3D FEFLOW model,
which are shown on Figures D-1 to D-2, respectively.
Table D-2: Summary of the Initial Boundary Conditions of 3D FEFLOW Model for IA
Area
Initial Boundary Condition
Figure
U/S River Bed
Total Head Ht=17.5 m (existing conditions)
Fig.D-1
D/S River Bed
Total Head Ht=3.0 m (existing conditions)
Surface of the North Spur
Fig.D-2
North Side of the Drift
Infiltration rate, q=1.2e-9m/s
Inflow flux boundary Qw (based on the function developed from
2D seepage analyses)
Inflow flux boundary QN= QW
South Side of Rock Knoll
No flow boundary
Fig.D-1
U/S Spur Slope Surface
Potential Seepage Face
Fig.D-1
Kettle Lakes Surface
Potential Seepage Face
Fig.D-1
D/S Surface of Spur
Potential Seepage Face
Fig.D-1
West Side of the Drift
Note:
1-
1
Fig.D-1
Fig.D-2
Fig.D-2
The Infiltration rate of q=1.2e-9 m/s into the spur surface was assumed to be 4% of the annual average
precipitation rate of 950 mm/y.
5.
Piezometeric Response under Initial Boundary Conditions
The results of steady seepage analysis from 3D FEFLOW model under initial geologic setting
and boundary conditions (see Table D-2) are summarised in Table D-3. The calculated
hydraulic contours in the drift is present in Figure D-3. From Table D-3, it can be seen that the
results from FEFLOW modelling significantly underestimated the hydraulic head in the
southern block of the model (piezometers C4, C3, D1, B8) for the initial boundary conditions,
which is the most critical part of the spur.
Table D-3: Summary of Comparison of the Calculated Piezometric Response with the
Measurement in IA Drift under Initial Boundary Conditions
Piezometers
Hydraulic Head (m)FEFLOW
Hydraulic Head (m)- 1979
Investigation
Error (%)
B6
E1
D4
B5
1
C4
1
C3
1
D1
1
B8
B7
37.20
32.40
27.90
25.20
21.80
19.80
19.70
17.00
10.00
39.40
27.60
25.00
32.50
26.30
27.20
28.20
24.20
9.20
5.58
17.39
11.60
22.46
17.11
27.21
30.14
29.75
8.70
1-
Note: the highlighted piezometers were installed in the drift within the southern block of the spur
Page 4
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6.
Calibration Scenarios (Sensitivity Studies)
A series of sensitivity studies (Scenarios) have been conducted to determine the main factors
could have induced a relatively high hydraulic head distribution within the southern block of
the Spur. The objectives of the sensitivity studies are to better understand the mechanism of
high piezometric readings in the southern block of the spur, and to determine the best and
most reasonable solution for the IA 3D FEFLOW model calibration, which is the basis to
simulate the proposed stabilization work for the North Spur.
6.1
Scenario 1-Sensitivity Study by Changing North-West Inflow Flux Rates
The objective for this study is to investigate the effect of various North-West (N-W) inflow flux
on the hydraulic head response of southern block. A total of 5 cases were carried out with the
-7
-7
N-W inflow flux rate increasing from 1x10 m/s to 6x10 m/s, respectively. Table D-4 shows
the results, which can be summarized as the following:
i)
The calculated hydraulic heads in the drift increased with increasing of the N-W flux
rates;
ii)
The hydraulic heads in southern block of the Spur (C4, C3,D1, B8 and B7) were
relatively less sensitive to the N-W flux compared to Northern block.
iii) The calculated hydraulic heads at the piezometers located in the southern block were
-7
still significantly underestimated even a maximum flux rate of 6x10 m/s was
assigned for the model.
Table D-4: Summary of Results of Scenario 1 (Changing the North-West Flux Rate)
N-W FLUX
(m/s)
1x10
2.5x10
Piezometer
Calculated
Head
Calculated
Head
Calculated
Head
Calculated
Head
Calculated
Head
Measured
Head
25.40
35.53
22.80
17.39
19.50
22.00
18.70
42.46
17.30
34.22
16.10
40.81
16.10
42.91
14.20
41.32
9.50
3.26
37.20
5.58
32.40
17.39
27.90
11.60
25.20
22.46
21.80
17.11
19.80
27.21
19.70
30.14
17.00
29.75
10.00
8.70
41.50
5.33
33.50
21.38
28.80
15.20
25.80
20.62
22.00
16.35
20.20
25.74
20.30
28.01
17.80
26.45
10.10
9.78
44.00
11.68
34.00
23.19
29.20
16.80
26.20
19.38
22.70
13.69
20.50
24.63
20.60
26.95
18.00
25.62
10.10
9.78
46.20
17.26
34.50
25.00
29.80
19.20
26.80
17.54
22.90
12.93
20.80
23.53
20.80
26.24
18.00
25.62
10.20
10.87
39.40
Error (%)
27.60
Error (%)
25.00
Error (%)
32.50
Error (%)
26.30
Error (%)
27.20
Error (%)
28.20
Error (%)
24.20
Error (%)
9.20
Error (%)
B6
E1
D4
B5
C4
1
C3
1
D1
1
B8
1
B7
-7
-7
-7
4x10
-7
5x10
-7
6x10
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
Page 5
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
6.2
Scenario 2- Sensitivity Study by Changing Infiltration Rate
The objective for this study is to investigate the effect of the infiltration rate (INF) on the
hydraulic heads distribution of the North Spur. The INF rates were increased from a minimum
-9
-8
value of 1.2x10 m/s to a maximum value of 7.5x10 m/s, which is corresponding to 4% and
248% of the average annual precipitation of 950mm/y, respectively. Table D-5 shows the
results, which can be summarized as the following:
i)
The calculated hydraulic heads in the drift increased with increasing of the INF rate
on the surface of the North Spur;
ii)
The calculated hydraulic heads at the piezometers located in the southern block were
-8
underestimated when the INF is less than 5x10 m/s, which is corresponding to
166% of the annual average precipitation of 950mm/y;
iii) The calculated piezometeric heads showed a comparable results to the
-8
measurement at INF rate of 7.5x10 m/s corresponding to about 248% of the annual
average precipitation. However, it should be noted that the assumed maximum INF
rate is 2.5 times higher than the average annual precipitation and is physically not
possible.
Table D-5: Summary of the Results of Scenario 2 (Changing INF rate)
-9
-8
-8
-8
-8
INF (m/s)
1.2x10
1x10
2.5x10
5x10
7.5x10
Piezometer
Calculated
Head
Calculated
Head
Calculated
Head
Calculated
Head
Calculated
Head
B6
E1
D4
B5
C4
1
C3
1
D1
1
B8
1
B7
Measured
Head
37.2
37.8
39.3
41.9
44
39.4
5.58
4.06
0.25
6.35
11.68
Error (%)
32.4
32.9
33.8
35.2
36.3
27.6
17.39
19.20
22.46
27.54
31.52
Error (%)
27.9
28.2
28.8
29.8
30.6
25
11.60
12.80
15.20
19.20
22.40
Error (%)
25.2
25.9
27.2
29.4
31.2
32.5
22.46
20.31
16.31
9.54
4.00
Error (%)
21.8
22.6
24.1
26.5
28.6
26.3
17.11
14.07
8.37
0.76
8.75
Error (%)
19.8
20.5
22.4
24.4
26.5
27.2
27.21
24.63
17.65
10.29
2.57
Error (%)
19.7
20.4
22.2
24.2
26.2
28.2
30.14
27.66
21.28
14.18
7.09
Error (%)
17
18
19
20.4
21.5
24.2
29.75
25.62
21.49
15.70
11.16
Error (%)
10
10.1
10.4
10.8
10.9
9.2
8.70
9.78
13.04
17.39
18.48
Error (%)
1-
Note: the highlighted piezometers were installed in the drift within the southern block of the spur
Page 6
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
6.3
Scenario 3- Extending the INF Surface to Cover D/S Scarp Surface
In this case study, the INF surface area was extended to cover the D/S scarps surface, which
was formed during past landslides. Figure D-4 shows modified boundary conditions for D/S
scarp surface. Table D-6 summarized the results. It can be seen that the extending INF
surface area caused an increasing in the piezometric readings of the IA drift (in particular
southern block). However, the hydraulic heads in the southern block were still significantly
underestimated for this scenario (i.e. the calculated results did not match the high existing
piezometric readings in the southern block of the spur).
Table D-6: Summary of the Results of Scenario 3 (Extending the INF Surface Area)
Piezometer No.
Hydraulic Head (m)
Measurement in1979
Hydraulic Head (m)
FEFLOW
Error (%)
B6
E1
D4
B5
1
C4
1
C3
1
D1
1
B8
B7
39.40
27.60
25.00
32.50
26.30
27.20
28.20
24.20
9.20
38.80
33.10
28.40
26.30
23.60
22.20
22.50
20.50
12.90
1.52
19.93
13.60
19.08
10.27
18.38
20.21
15.29
40.22
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
6.4
Scenario 4- Extending the INF Surface Area and Changing Hydraulic
Conductivity of Lower Silty Sand Drift Zone-B of Southern Block of the
Spur
For Scenario 4, the permeability values for the lower silty sand drift -Zone B material has
-6
-8
been decreased from 8x10 m/s to 8x10 m/s, and the INF surface area was extended to
D/S scarps. Table D-7 is a summary of the results for this scenario. It can be seen that the
calculated hydraulic heads just slightly increased with decreasing the permeability values of
the lower drift zone B of the southern block of the Spur, but the modeling results were still
significantly underestimated the measured hydraulic heads in the southern block of the spur.
Page 7
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-7: Summary of the Results of Scenario 4 (Extending INF Surface Area and Changing K of
Lower Silty Sand Drift Zone B)
kx=ky= 8x10 m/s
kx=ky= 8x10 m/s
kx=ky= 8x10 m/s
Measured
Hydraulic Head
(m)
38.8
1.52
33.1
19.93
28.4
13.60
26.3
19.08
23.6
10.27
22.2
18.38
22.5
20.21
20.5
15.29
12.9
40.22
38.9
1.27
33.1
19.93
28.4
13.60
26.6
18.15
24.4
7.22
22.8
16.18
23.2
17.73
21.5
11.16
13.9
51.09
38.9
1.27
33.1
19.93
28.5
14.00
26.6
18.15
24.8
5.70
22.9
15.81
23.4
17.02
21.8
9.92
14
52.17
39.4
Error (%)
27.6
Error (%)
25
Error (%)
32.5
Error (%)
26.3
Error (%)
27.2
Error (%)
28.2
Error (%)
24.2
Error (%)
9.2
Error (%)
Calculated Hydraulic Heads (m)- FEFLOW
Piezometer
-6
B6
E1
D4
B5
C4
1
C3
1
D1
1
B8
1
B7
-7
-8
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
6.5
Scenario 5- Extending the INF Surface Area and Introducing INF from
Rock Knoll Surface
In this scenario study, the infiltration from the rock knoll surface has been taken into
consideration to investigate the effect on the hydraulic heads in southern block of the Spur. It
should be noted that the rock knoll was not included in the current 3D FEFLOW model.
Therefore, the assumed flux from the rock knoll surface was transferred to the southern block
of the Spur (i.e. introduce an additional flux into southern block which was equivalent to the
flux into rock knoll area). The following summarized the flux calculation:
2
i)
Total surface area of the rock knoll, AR is about 134,400 m ;
ii)
INF rate in the North Spur area is 1.2x10 m/s;
-9
-4
3
iii) Total flux from Rock Knoll, QR is about 1.61x10 m /s (QR * INF)
2
iv) Total of surface area of the north sour neck, AN is about 20,458 m ;
-8
v) Additional flux rate per unit area into the spur neck area is rounded 1x10 m/s (QR /
AN)
Figure D-5 shows the modified boundary conditions on the neck of the Spur area. Table D-8
summarized the results for this Scenario. It can be seen that this additional flux caused the
hydraulic heads in the southern block to increase, but still significantly underestimated the insitu piezometeric measurements.
Page 8
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-8: Summary of the Results of Scenario 5 (Introducing Additional Flux from Rock Knoll
Surface Area)
Measured Hydraulic
Calculated Hydraulic Head from
Piezometer
Error (%)
Head in 1979 (m)
FEFLOW Model (m)
B6
39.40
38.80
1.52
E1
27.60
33.10
19.93
D4
25.00
28.50
14.00
B5
32.50
26.40
18.77
C4
1
26.30
23.90
9.13
C3
1
27.20
22.40
17.65
D1
1
28.20
22.60
19.86
1
24.20
20.80
14.05
9.20
13.10
42.39
B8
B7
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
6.6
Scenario 6 - Increasing the INF Surface Area, Introducing Additional INF
from Rock Knoll Surface and Adjusting Permeability of Drift Materials
This scenario considered the comprehensive factors including: a) increase the INF surface
area to include the D/S scarps surface; b) introduce an additional INF from the Rock Knoll
surface area and; c) decrease the permeability for both the drift materials zone A and zone B
-9
to 8x10 m/s. Table D-9 summarizes the results for this Scenario. From Table D-9, it can be
seen that a comparable results were obtained from FEFLOW model comparing with the
existing piezometric data under long-term steady seepage conditions.
To calibrate the model for pumping test based on the boundary conditions of Scenario 6, a
transient seepage analysis was carried out to simulate the pumping tests of 1981. Three
pump wells (W3, W10 and W17) were operated at different pumping rates and durations.
Figure D-6 shows the location of the pump wells. Table D-10 is the summary of the pumping
test results (drawdowns) from FEFLOW model and in-situ piezometric measurement data. It
can be seen that in general most of piezometers in the IA showed no response (drawdown),
which could be mainly due to low permeability of drift materials. Therefore, the FE model
cannot be calibrated for pumping tests for this scenario.
Table D-9: Summary of the Results for Scenarios 6 under Steady Seepage Condition
Piezometer
Measured Hydraulic
Head in 1979 (m)
Calculated Hydraulic Head
from FEFLOW Model (m)
Error (%)
B6
E1
D4
B5
1
C4
1
C3
1
D1
1
B8
B7
39.4
27.6
25
32.5
26.3
27.2
28.2
24.2
9.2
39.2
33.3
28.8
28
27.2
26.4
26.4
25.2
18
0.51
20.65
15.20
13.85
3.42
2.94
6.38
4.13
95.65
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
Page 9
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-10: Summary of Results of Pumping Tests for Scenario 6
3
W3: 108 m /day for 69 hours (2.875 day)
3
W10: 11.23 m /day for 8 hours and 40 mins (0.36 day)
3
W17: 10.37 m /day for one and half hours (0.0625 day)
Calculated Hydraulic Head from
FEFLOW Model (m)
Piezometric Measurement in
1981 during Pumping Test
Piezometers
Before
pumping (m)
After
pumping (m)
Drawdown
(m)
Drawdown
(m)
W1
26.3
26.3
0
0.3
W2
26.4
26.2
0.2
2.14
W3
26.5
-190
216.5
6.44
W4
26.7
26.5
0.2
1.46
W5
26.8
26.8
0
1.9
W6
26.9
26.9
0
0.81
W7
27
27
0
0.38
P1
26.1
26.1
0
0.13
P2
26.2
26.2
0
0.32
P3
26.4
26.4
0
1.28
P4
26.7
26.7
0
1.88
P5
26.8
26.8
0
1.51
P6
26.8
26.8
0
0.15
P15
26.5
26.5
0
1.81
6.7
Scenario 7- Increasing the INF Surface Area, Introducing Additional INF
from Rock Knoll Surface and Increase Permeability for Silty Clay layers
of the Spur
Scenario 7 has been carried out to investigate the impact of permeability of the silty clay layer
in the drift on the hydraulic heads response of IA. The permeability values of the silty clay
-7
-6
layers were increased from 1x10 m/s to 1x10 m/s in the model. Table D-11 summarizes
the results. From Table D-11, the calculated hydraulic heads in the IA decreased with
increasing K values of the silty clay layers and the calculated results still underestimated the
hydraulic heads in southern block of the Spur.
Page 10
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-11: Summary of the results for Scenario 7
Piezometer
B6
E1
D4
B5
C4
1
C3
1
D1
1
B8
1
B7
Calculated hydraulic Head from FEFLOW Model (m)
-7
-7
-6
K= 1x10 m/s
K= 5x10 m/s
k= 1x10 m/s
38.9
1.27
33.1
19.93
28.6
14.40
26.6
18.15
24.2
7.98
22.8
16.18
22.8
19.15
20.6
14.88
13
41.30
36.3
7.87
32.9
19.20
27.8
11.20
25
23.08
23.8
9.51
22.2
18.38
22.2
21.28
19.8
18.18
12.2
32.61
Measured Hydraulic Head (m)
35.9
8.88
32.8
18.84
27.3
9.20
25.2
22.46
23.4
11.03
21.8
19.85
21.5
23.76
19.2
20.66
11.9
29.35
39.4
Error (%)
27.6
Error (%)
25
Error (%)
32.5
Error (%)
26.3
Error (%)
27.2
Error (%)
28.2
Error (%)
24.2
Error (%)
9.2
Error (%)
Note:1-the highlighted piezometers were installed in the drift within the southern block of the spur
6.8
Scenario 8 - Increasing the INF Surface Area and Conducting Flux from
Southern Fractured Bedrock Surface
This Scenario assumed additional flux sources coming from the fractured bedrock surface
-6
around the south side to feed the IA. A flux rate of 3x10 m/s per unit area was estimated to
enter the IA along the interface of Rock Knoll-to-IA with a total flux feeding area of about
2
10,000 m . Figure D-7 shows the modified boundary conditions for this scenario. Tables D12, D-13, and D-14 summarizes calibration results for the existing steady seepage condition,
short term pumping test and long-term pumping tests, respectively.
Based on the results, it can be seen that the calculated results from FEFLOW model were
very comparable with the in-situ measurements for both steady seepage conditions and
transient condition for pumping tests. However, the introduced flux from the fractured bedrock
rock surface at the south side need to be confirmed because the bedrock at site has low
permeability based on the packer testing.
Page 11
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-12: Summary of the Results for Scenario 8 under Steady Seepage Conditions
Piezometer
Measured Hydraulic Head in 1979 (m)
Calculated Head from FEFLOW Model (m)
Error (%)
B6
39.40
39.50
0.25
E1
27.60
33.30
20.65
D4
25.00
28.80
15.20
B5
32.50
27.80
14.46
C4
1
26.30
27.70
5.32
C3
1
27.20
28.50
4.78
D1
1
28.20
27.20
3.55
1
24.20
24.00
0.83
9.20
13.50
46.74
B8
B7
1-
Note: the highlighted piezometers were installed in the drift within the southern block of the spur
Table D-13: Summary of Results for Short Term Pumping Test of Scenario 8
3
W3: 108 m /day for 69 hours (2.875 day)
3
W10: 11.23 m /day for 8 hours and 40 mins (0.36 day)
3
W17: 10.37 m /day for one and half hours (0.0625 day)
Piezometers
Before pumping
(m)
After pumping
(m)
Drawdown
(m)
1981 PUMPING
TEST
Drawdown
(m)
W1
28.4
27.9
0.5
0.3
W2
27.9
26.3
1.6
2.14
W3
27.6
21.7
5.9
6.44
W4
27.4
25.7
1.7
1.46
W5
27.4
26.2
1.2
1.9
W6
27.3
26.6
0.7
0.81
W7
27.2
26.8
0.4
0.38
P1
31.9
31.8
0.1
0.13
P2
27.8
26.1
1.7
0.32
P3
27.5
25.6
1.9
1.28
P4
27.2
26
1.2
1.88
P5
27
26.5
0.5
1.51
P6
26.6
26.4
0.2
0.15
P15
27.2
25.8
1.4
1.81
P16
27.2
26.2
1
0.75
P17
27.2
26.3
0.9
0.82
FEFLOW 3D MODEL
Page 12
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-14: Summary of Long Term Pumping Test for Scenario 8
3
Pump Wells
Duration
Piezometer
6.9
W1-W7: 80.64 m /day;
After 13 months
Calculated
Measured
Drawdown (m)
Drawdown (m)
3
W8-W22: 14.4 m /day
After 27 months
Calculated
Measured
Drawdown (m)
Drawdown (m)
P1
4.5
0.3
5.9
1.2
P2
20.6
12.45
22.8
13.85
P3
23.2
11.19
9.5
12.44
P4
22.0
17.91
24.0
-
P5
15.0
16.87
17.0
18.97
P6
6.5
3.92
7.8
4.77
P7
3.0
2.8
4.2
3.35
P8
4.0
4.91
4.3
5.56
P9
2.9
0.65
3.2
0.4
P10
1.5
0.14
2.0
0.39
P11
1.3
0.19
1.4
0.49
P12
1.0
-0.25
1.4
-0.3
P13
1.1
1.33
1.3
1.38
P14
1.2
0.1
1.7
0.3
P15
21.4
19.14
24
19.69
P16
14.7
8.1
16.7
8.8
P17
7.5
7.32
9.0
8.08
Scenario 9-Blockage of D/S Scarps Slope Surface
The Scenario considered a layer of low permeable materials blocked the D/S surface in the
old failure scarps. This material is thought to be slope debris from prior landslides (adjacent to
Rock Knoll of southern block). The thickness of the impermeable layer is assumed 1 m in the
-8
FEFLOW model with the permeability of 1 × 10 m/s . Figure D-8 shows the blockage of D/S
scarps surface. Tables D-15, D-16 and D-17 show the results relative to the different case
studies for model calibrate, including existing steady seepage condition, short term pumping
test and long-term pumping tests, respectively. Figures D-9 to D-12 show the hydraulic head
contours for both steady seepage and transient analysis.
The results obtained from FEFLOW model were in a good agreement with the piezometric
measurements for all the calibration cases.
Based on the results from FEFLOW model for scenario 9, the FEFLOW model for IA was in
general successfully calibrated by the consideration of the blockage of D/S scarps slope
surface, this low permeable materials were from the debris of the old landslides which
prevents the free drainage path of IA from downstream and cause a relatively high
piezometric readings in southern block of the spur. Consequently, Scenario 9 was selected to
be the basis model for further case studies.
Page 13
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-15: Summary of the Results for Scenario 9 under Steady Seepage Condition
Piezometers
Measured Hydraulic
Head (m)
Calculated Hydraulic Head
from FEFLOW Model (m)
Error (%)
B6
39.40
38.80
1.52
E1
27.60
33.50
21.38
D4
25.00
29.50
18.00
32.50
28.90
11.08
C4
B5
1
26.30
27.30
3.80
C3
1
27.20
26.30
3.31
D1
1
28.20
26.80
4.96
1
24.20
26.00
7.44
P2
24.95
26.50
6.21
P3
30.84
26.80
13.10
P4
28.91
27.20
5.91
P5
28.17
27.40
2.73
B8
P6
26.57
27.60
3.88
P14
26.40
26.30
0.38
P15
28.00
26.70
4.64
P17
29.03
27.10
6.65
1-
Note: the highlighted piezometers were installed in the drift within the southern block of the spur
Table D-16: Summary of the Results Short Term Pumping Test for Scenario 9
3
W3: 108 m /day for 69 hours (2.875 day)
3
W10: 11.23 m /day for 8 hours and 40 mins (0.36 day)
3
W17: 10.37 m /day for one and half hours (0.0625 day)
Piezometers
Before pumping (m)
After pumping (m)
Drawdown (m)
Measurement in
1981 PUMPING TEST
Drawdown (m)
W1
W2
W3
W4
W5
W6
W7
P1
P2
P3
P4
P5
P6
P15
P16
P17
26.3
26.5
26.6
26.7
26.9
26.9
27.4
26.2
26.5
26.7
26.8
27.2
27.7
26.7
26.8
27
25.8
24.6
20.8
24.9
25.9
26.5
27.1
26.1
26
25
25.8
27
27.5
25.7
26.1
26.1
0.5
1.9
5.8
1.8
1.0
0.4
0.3
0.1
0.5
1.7
1.0
0.2
0.2
1.0
0.7
0.9
0.3
2.14
6.44
1.46
1.9
0.81
0.38
0.13
0.32
1.28
1.88
1.51
0.15
1.81
0.75
0.82
Calculated Hydraulic Head from FEFLOW Model (m)
Page 14
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Table D-17: Summary of the Results Long Term Pumping Tests for Scenario 9
3
W1-W7: 80.64 m /day;
Piezometers
After 13 months Pumping
Calculated
Measured
Drawdown (m)
Drawdown (m)
3
W8-W22: 14.4 m /day
After 27 months Pumping
Calculated
Measured
Drawdown (m)
Drawdown (m)
P1
7.7
0.3
9.9
1.2
P2
13.3
12.45
14.4
13.85
P3
14.5
11.19
16.0
12.44
P4
14.2
17.91
16.4
-
P5
11.7
16.87
22.2
18.97
P6
7
3.92
9.5
4.77
P7
5
2.8
6.3
3.35
P8
4.7
4.91
5.65
5.56
P9
3.4
0.65
4.2
0.4
P10
2.9
0.14
3.6
0.39
P11
1.8
0.19
2.5
0.49
P12
1.6
-0.25
2.3
-0.3
P13
3.5
1.33
4.3
1.38
P14
1.8
0.1
2.5
0.3
P15
13.9
19.14
15.9
19.69
P16
10.8
8.1
12.8
8.8
P17
10.1
7.32
12.0
8.08
Page 15
© Hatch 2015 All rights reserved, including all rights relating to the use of this document or its contents.
Seepage Faces
U/S Ht= 17.5 m
D/S Ht = 3 m
No Flow
Figure D-1
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions for IA 3D FEFLOW Model
Rock knoll
Infiltration (1.2x10-9 m/s)
D/S
U/S
D/S
Inflow Flux QW
Inflow Flux QN
Figure D-2
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Boundary Conditions for IA 3D FEFLOW Model-Cont’d
Figure D-3
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Response of IA at Initial Conditions
Extended Area of Infiltration (1.2x10-9 m/s)
U/S
Rock Knoll
D/S
Figure D-4
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Extended INF Surface Covering D/S Scarps
Neck Area = 20458.5 m2
QN= 1x10-8 m/s/unit area
Rock Knoll Surface Area= 134,400 m2
INF = 1.2 x 10-9 m/s/unit area
QR= 1.62x 10-4 m3/s
Figure D-5
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Assumed Possible INF Coming from the Rock Knoll Surface
Existing dewater system installed in 1981
Figure D-6
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Pump Well System (W1-W22) in the 3D FEFLOW Model
Area= 10,000 m2
FLUX= φS= 3x10-6 m/s
A
B
B
A
Cross section A-B
Rock knoll
Figure D-7
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Plan View and Cross Section of Rock Knoll-to-IA Interface with Flux from Fractured Bedrock Surface
Blockage of D/S Scarps slope surface
U/S
D/S
Figure D-8
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
FEFLOW 3D Model Showing the Impervious Layer Covering the D/S Slopes
Figure D-9
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Calculated of Hydraulic Head Contours under Steady Seepage Conditions
for Scenario 9 -Blockage of D/S Slopes
Figure D-10
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Contours of Calculated Hydraulic Heads for Short Term Pumping Test (Scenario 9)
Figure D-11
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Contours of Calculated Hydraulic Heads for 13 months Pumping Test (Scenario 9)
Figure D-12
Ontario Power Generation
3D Hydrogeological Study for the North Spur
PGS Reservoir Assessment of Protective Measures
Contours of Calculated Hydraulic Heads for 27 months Pumping Test (Scenario 9)
Suite E200, Bally Rou Place, 370 Torbay Rd.
St. John's, Newfoundland, Canada A1A 3W8
Tel (709) 754 6933  Fax (709) 754 2717
Suite E200, Bally Rou Place, 370 Torbay Rd.
St. John's, Newfoundland, Canada A1A 3W8
Tel (709) 754 6933  Fax (709) 754 2717