GEO 440
Homework 3
Homer Hazardous Waste Site II: Hydrogeologic Investigation
Due: September 19
Overview: We will we be continuing the series of exercises that walk you through the modeling
process. The overall exercise examines a hazardous waste site and the potential contamination at
the site. The exercises are typical of studies that you may encounter as an environmental
consultant.
Purpose: Continued development of a conceptual model, incorporating the hydrogeologic
information.
Objectives: Interpret the available data and evaluate the possible aquifers.
Establish the nature and extent of the hydrostratigraphic unit(s) by making an
isopach map.
Develop a fluid potential map for the aquifer(s), and determine the ground water
flow direction.
PROCEDURES
Define Aquifers
1) In the last exercise (HW 2), you made an interpretation of the hydrostratigraphy of the site.
Did you suggest that there is one or two aquifers? If more than one, were the aquifers part of
the same flow system-that is, are they hydraulically connected-or are there two independent
flow systems?
2) If you could measure standing water levels in two wells side by side, one open at depth and
the other only shallow, how would this information help you answer this question?
a) If the two levels were exactly the same, what would you infer?
b) If the level in the deep well were higher, what would you infer?
3) Return to the cross sections you made in the last lab, and plot on them the water levels
recorded April 8, 1990, in each of the deep wells (Water Levels in Deep Wells, April 8, 1990
[Table 1]). Use a red line to connect the water levels. Note that for GB-2 at the northwest end
of the section, you can use data from 308-D nearby. Similarly, you can get information from
shallow wells that were drilled and monitored next to each of the deep wells. Referring to the
site map, you can see at the northwest end, for example, 308-A, a shallow well, is adjacent to
308-D.
Plot data from Water Levels in Shallow Wells, April 8, 1990 (Table 2), on the cross sections
also, using blue for these measurements.
a) Considering the relationship of the upper potentiometric surface to the stratigraphy, is the
upper aquifer confined, unconfined, or semi-confined?
4) Describe and interpret the relationship of the two potentiometric lines.
Construct an Isopach Map of the Confining Layer
5) Once you have established the relationship of the upper and lower aquifers and your cross
section 1 shows some limitation to the separateness of these aquifers, it would be instructive
to determine the three-dimensional nature of the confining layer. In addition to the geologic
logs, some information is available from a temporary well point program (Table 3). Using
both of these data sources, construct an isopach map for the confining layer on the site base
map, Figure 1.
6) Describe the geometry of the confining layer, and suggest an explanation for it.
Determine the Groundwater Flow in the Upper Aquifer
7) Construct a map of the potentiometric surface of the upper aquifer on Figure 2. With blue
arrows, draw sufficient flow lines to show the groundwater flow throughout the site.
8) One could use this map to estimate actual travel paths of groundwater. For example, where
would you expect groundwater to flow from the area of well 204? Draw a green flow line
from 204B to the Von Fange Ditch. Where along the ditch (nearest which well) would you
expect this flow to occur?
9) Where does recharge to this aquifer probably occur?
Show the Groundwater Flow in the Lower Aquifer
10) Construct a map of the potentiometric surface of the lower aquifer on Figure 3. With red
arrows, draw sufficient flow lines to show the groundwater flow throughout the site.
11) Where does recharge probably occur?
12) Compare the heads from the two potentiometric maps north of the Von Fange Ditch. What do
you think is happening in this area?
Summary of Hydrogeology
13) Summarize, in a few paragraphs, the hydrogeology of the site, making reference to your
maps and sections.
Table 1: Water Levels in Deep Wells
April 8, 1990
Well
Water-Level Elevation
(ft above m.s.l.)
132
140
145
220
221
222
223
224
225
226
227
308D
355
556.80
556.65
556.49
551.59
550.69
551.15
550.82
556.32
556.64
556.91
555.34
555.43
556.62
Table 2: Water Levels in Shallow Wells
April 8, 1990
Well
Water-Level Elevation
(ft above m.s.l.)
131
556.40
133
557.37
134
558.55
135
557.50
136
558.04
137
559.01
138
557.79
141
558.79
142
560.18
144
563.67
146
560.31
147
561.15
200
570.11
201
561.75
202A
559.80
203A
560.80
204A
559.78
205A
559.82
206A
559.16
207A
558.46
208A
558.43
209A
559.08
210A
558.72
211A
557.04
212A
556.78
213A
559.41
305A
557.73
306A
556.54
308A
555.43
A
557.92
B
554.83
F
554.22
G
554.77
M
555.03
N
557.10
Table 3: Supplementary Confining Layer Data from Temporary Well Points
Well Point Ground Elevation Bedrock Elevation Top of Confining
(ft)
(ft)
Layer Elevation
(ft)
1
552
not encountered
502
2
561.7
not encountered
501.7
3
563.1
not encountered
503.1
4
562.7
not encountered
503.7
5
560.9
not encountered
503.9
9
565.5
not encountered
505.5
10
566.0
494.0
506.0
11
562.7
not encountered
501.7
12
562.2
not encountered
503.2
13
562.4
not encountered
507.4
14
562.2
494.0
507.2
15
562.3
492.3
not found
16
561.8
492.8
not found
17
562.3
488.8
not found
18
559.8
494
not found
20
564
496
not found
21
558.7
493.2
not found
Homer
Figure 1: Isopach base map of the confining layer, Homer hazardous waste site.
Homer
Figure 2: Potentiometric surface and ground water flow in the upper aquifer.
Homer
Figure 2: Potentiometric surface and ground water flow in the lower aquifer.