2-YEAR POST-TRANSPLANT
EELGRASS SURVEY
FOR THE SAN DIEGO GAS & ELECTRIC
SILVERGATE 138 KV HORIZONTAL DRILLING FRAC-OUT
AT THE SWEETWATER MARSH, CHULA VISTA, CALIFORNIA
Prepared for:
TRC
Attn: Mr. Michael Mezey
1903 Wright Place, Suite 190
Carlsbad, CA 92008
Prepared by:
Merkel & Associates, Inc.
5434 Ruffin Road
San Diego, CA 92123
Phone: (858) 560-5465
Fax: (858) 560-7779
August 2010
Keith Merkel, Principal Consultant
2-Year Post-Transplant Eelgrass Survey
August 2010
TABLE OF CONTENTS
INTRODUCTION ........................................................................................................................................ 1
TRANSPLANT SITE HISTORY AND LAYOUT...................................................................................... 1
MITIGATION SUCCESS CRITERIA......................................................................................................... 4
SURVEY METHODOLOGY ...................................................................................................................... 4
RESULTS ..................................................................................................................................................... 4
Eelgrass Transplant Site ............................................................................................................................ 4
Reference Site ........................................................................................................................................... 5
DISCUSSION ............................................................................................................................................... 5
REFERENCES ............................................................................................................................................. 7
LIST OF FIGURES
Figure 1. Vicinity Map –Site of SDG&E Project Work, National City, CA .............................................. 2
Figure 2. Eelgrass Coverage in the Area of Potential Effect and Control Site. .......................................... 3
Figure 3. Transplant eelgrass coverage relative to reference area and restoration equirements ................. 6
Figure 4. Transplant area eelgrass shoot density relative to reference area shoot density.......................... 6
LIST OF APPENDICIES
Appendix A. Southern California Eelgrass Mitigation Policy (Revision 11) Monitoring and Reporting
Compliance Summary
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2-Year Post-Transplant Eelgrass Survey
August 2010
INTRODUCTION
Merkel & Associates, Inc. (M&A) was retained by TRC to conduct an eelgrass (Zostera marina)
transplant in support of the SDG&E Silvergate 138kV Horizontal Directional Drilling (HDD) Project
(Project) at the Sweetwater Marsh, Chula Vista, California (Figure 1). The undergrounding of the
Silvergate transmission line across the Sweetwater River Marsh and Sweetwater River Flood Control
Channel was completed using horizontal directional drilling methods; however, frac-outs sometimes
occur where drilling muds and cutting sediments are discharged to the surface through fissures. On
October 16, 2007, a frac-out occurred that discharged materials consisting of sand and drill muds into
the historic channel of the Sweetwater River and overran eelgrass beds at the frac-out location.
Despite clean-up operations conducted by M&A on October 25 and 26, 2007, residual eelgrass bed
disturbance was determined to be 99.6 m2 (0.02 acre).
The Southern California Eelgrass Mitigation Policy (NMFS, Revision 11) (SCEMP) governs eelgrass
mitigation requirements for the proposed work. Based on comparisons between the pre-impact
conditions and the post-impact assessment, the losses are considered to be temporary and less than
100 m2. As such, the impacts meet the exception clause to the 1.2:1 mitigation requirements within
provision 5. Mitigation Size of the SCEMP. This provision allows that mitigation on a 1:1 basis shall
be acceptable for projects that meet these conditions.
The transplant was conducted on July 24, 2008 in accordance with the mitigation plan prepared for
this Project (M&A 2008a). Upon completion of the transplant effort, a monitoring program was
initiated and is scheduled to continue for 60 months (i.e., 5 years). The monitoring program will be
conducted at intervals of 3, 6, 12, 24, 36, 48, and 60 months post-transplant. When monitoring dates
fall outside the normal eelgrass-growing season (April - October), monitoring dates may be shifted to
coincide with the next eelgrass-growing season.
TRANSPLANT SITE HISTORY AND LAYOUT
Eelgrass restoration was conducted within the footprint of damage caused by the frac-out. Early
clean-up of sediments restored the elevations of the channel to pre-discharge conditions and retained
sediment character by removal of all sediments down to the organic layer defined by the dead
eelgrass that was buried by the sediment overrun. As such, this area is anticipated to be an ideal area
for restoration of eelgrass, and risks of transplant failure are considered to be very low.
A total of approximately 99.6 m2 (0.02 acre) of eelgrass was planted within the restoration area
(Figure 2) in a transplant that was conducted on July 24, 2008 at the site of the Silvergate Horizontal
Directional Drilling site in the Sweetwater River Marsh main tidal channel. 400 planting units were
transplanted to the restoration area (M&A 2008b). This eelgrass transplant was performed in
accordance with transplant methods discussed in the Eelgrass Restoration Plan (M&A 2008a).
Eelgrass reference sites were established near the restoration site and include the surrounding native
eelgrass beds within the Sweetwater Marsh channel. These sites were selected based on proximity
to, and similarity in, biological characteristics to the restoration site. Monitoring of the reference
areas will be conducted coincident with the monitoring of the restoration area. Changes in the
reference area over time will be considered when evaluating the performance of the restoration area.
A prior reference area within the Sweetwater River Flood Control Channel (FCC) has been
monitored for purposes of pre-construction and post-construction assessments. This reference area,
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Project Area
Image Source:
USGS
N
W
Project Vicinity Map
E
S
1:24000
Silvergate Directional Boring Work
Frac-Out Damage Recovery Monitoring
Figure 1
August 2008
Merkel & Associates, Inc.
M&A # 05-111-06
Reference Area
Silvergate Frac-out Transplant Area
Eelgrass July 2009
0
Eelgrass August 2010
µ
5
10
Post-Transplant Eelgrass Survey for the
SDG&E Silvergate 138kV Horizontal Directional Drilling Frac Out
Sweetwater Marsh, Chula Vista, California
Twenty-four Month Monitoring
20
Meters
Figure 2
Merkel & Associates, Inc.
2-Year Post-Transplant Eelgrass Survey
August 2010
however, is not considered to be a suitable reference to the present site given its distance from the
frac-out area and differing environmental conditions. As a result, this area will not be monitored as a
reference in the future.
MITIGATION SUCCESS CRITERIA
This eelgrass-monitoring program includes milestone success monitoring to verify that minimum
coverage and density requirements are achieved per the requirements of SCEMP. The coverage and
leaf shoot density of eelgrass within the transplant and control areas will be mapped and measured at
each monitoring interval. The mitigation will be deemed successful when it has met the success
criteria outlined in the SCEMP. Criteria for determination of transplant success will be based upon
measurements of vegetative coverage (area) and leaf shoot density (shoots per square meter) and the
success milestones listed below. Fluctuations in eelgrass coverage and density at the mitigation site
will be compared to the control site in order to account for natural variations in the eelgrass bed. Key
success criteria are as follows:
A)
A minimum of 70 percent areal coverage and 30 percent density should be achieved after the
first year.
B)
A minimum of 85 percent areal coverage and 70 percent density should be achieved after the
second year.
C)
A minimum of 100 percent areal coverage and 85 percent density should be achieved for the
third, fourth, and fifth years.
Areas that do not meet the above success criteria will be replanted, and monitored for another fiveyear period, until the final goal is achieved. Should re-planting of the areas at the project site fail to
meet the success criteria; an alternative mitigation site will be selected to carry out revegetation.
Should the reference area fail or decline alongside the mitigation area for reasons outside the control
of SDG&E, SDG&E will not be held responsible for similar declines in the mitigation area.
SURVEY METHODOLOGY
M&A staff, Keith Merkel and Kathy Rogers, conducted the 24-month post transplant survey on
August 11, 2010. Data were collected at low tide and consisted of eelgrass areal coverage and
density investigation. Delineation of eelgrass location in the APE was made by walking the eelgrass
bed boundary with a hand-held differential GPS at low tide.
The density of actively growing turions (leaf shoots) was determined by conducting turion counts
within a 1/16-m2 quadrat throughout the transplant area. Ten replicate quadrats were randomly
placed within the eelgrass beds of the transplant and reference areas, respectively, to obtain a mean
turion density.
RESULTS
EELGRASS TRANSPLANT SITE
The current 24-month survey revealed 97.3 m2 (0.02 acre) of eelgrass within the transplant area
(Figure 2). The eelgrass leaf shoot densities (± 1 SD) were 851.2 ± 212.0 (n=10) shoots per square
meter.
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2-Year Post-Transplant Eelgrass Survey
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REFERENCE SITE
The current 24-month survey revealed a total of 375.9 m2 (0.09 acre) of eelgrass within the reference
site (Figure 2). This reference site lies partially within the APE for the OMPPA investigations that
have been previously conducted. The APE was selected as a reference area since it has a monitoring
history, appears to be relatively stable, and has fully recovered from prior damage associated with the
OMPPA project. The eelgrass leaf shoot density (± 1 SD) within the reference area was 948.8 ±
491.8 shoots per square meter (n=10).
DISCUSSION
During the transplant at the site of the SDG&E 138 kV Horizontal Directional Drilling Project,
99.6m2 (0.02 acre) of eelgrass were planted (Figure 3). Eelgrass coverage has remained relatively
constant since the initial transplant and cannot exceed the 99.6 m2 (0.02 acre) maximum since the
impact bed occurs completely within the reference area. A slight, 3.6 percent decline in the
transplant area from 99.6 m2 (0.02 acre) to 96.0 m2 (0.02 acre) was observed during the same period
when the reference area exhibited a 6.9 percent decline (Figure 3). In both instances, the declines
observed were defined by a decrease in the eelgrass extent along the shoreline margin where summer
season desiccation stress typically results in losses of eelgrass at higher elevations (Figure 2).
Through time, eelgrass transplant and reference areas have been increasing in density, with the
exception of the slight decline in the reference area density during the initial 6-month monitoring
period (Figure 4). The border between the two areas has been indistinguishable since the 6-month
survey. The transplant area is fully vegetated
with eelgrass throughout its core. Eelgrass
density within both the control and transplant
areas is remarkably high and indicative of the
shallow nature of the site combined with good
tidal flushing across the site. During the August
2010 survey, three replicate quadrats within the
transplant area were found to support a
remarkable 1,000+ turions/m2, and five replicate
quadrats within the reference area were found to
support over 1,000 turions/m2. While these
numbers are not uncommon on high shoreline
margins, the shallow and protected nature of the
historic Sweetwater River has allowed the plants
to obtain fairly robust condition while still High density eelgrass from Silvergate Frac-out
2
achieving the high turion density. This results in restoration transplant in 1/16 m quadrat (August
a closed canopy and thick eelgrass bed over much 2010).
of the monitored area both within and outside of
the transplant location.
Heavy macroalgal loads were observed along the edges on both the transplanted area and native
reference area. While algal loading is fairly heavy on the fringes of the eelgrass bed, the plants
themselves remain healthy. Given the high eelgrass density and warm waters present within the site,
a late summer decline in the beds may be expected. Such significant die-offs of eelgrass in large
patches have been observed in similar situations on numerous occasions. These declines appear to be
natural and generally are of short duration when they do occur. While the mechanisms triggering
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2-Year Post-Transplant Eelgrass Survey
August 2010
450
405
Transplant
400
Eelgrass Coverage (m2)
377
350
376
Reference
314
316
Requirement
300
250
200
150
99.6
100
94.0
99.6
97.3
96.0
50
0
7/24/2008
9/20/2008
1/9/2009
7/24/2009
8/11/2010
Transplant
3-month
6-month
12-month
24-month
36-month
48-month
60-month
Figure 3. Transplant eelgrass coverage relative to reference area and restoration requirements
1600.0
Transplant
1400.0
Reference
2
Shoot Density (turions/m )
1200.0
1000.0
800.0
600.0
400.0
200.0
0.0
7/24/2008
Transplant
9/20/2008
3-month
1/9/2009
6-month
7/24/2009
12-month
8/11/2010
24-month
Transplant
69.1
150.5
230.4
531.2
851.2
Reference
533.0
335.3
227.2
382.4
948.8
36-month
48-month
60-month
Figure 4. Transplant area eelgrass shoot density relative to reference area shoot density
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2-Year Post-Transplant Eelgrass Survey
August 2010
such diebacks remain unclear, they do appear to occur with relatively high frequency when the beds
exhibit conditions similar to those reflected at the Silvergate frac-out transplant site and reference
area. Typically, these diebacks occur during late summer if they are going to occur, and eelgrass
recovers in a less dense condition by the late spring of the subsequent year. It should be noted,
however, that these same conditions existed at the time of the 12-month monitoring, but no die-off
has yet occurred.
The transplant has a target objective of restoring eelgrass to the 99.6-m2 (0.02 acre) frac-out impact
area. After the second year post-transplant, the SCEMP requires eelgrass to achieve 85% of the
coverage and 70% of the reference bed density. This restoration objective is currently being met,
with only one small area along the south-eastern edge currently being unvegetated. The second year
success criterion is a cover of 84.7 m2. While the bed presently achieves a 97.3 m2 coverage, the
density of the reference bed and transplant bed are statistically the same with the mean of the
reference bed exceeding that of the transplant by 10.5% and with both beds exhibiting broad
variability in turion densities.
It is anticipated that during the cooler winter months, beds may expand shoreward allowing the full
restoration of the transplant area. The transplant beds are presently indistinguishable from the
surrounding native beds and are only detectible through the presence of various monument stakes
placed at the time of the transplant. It is anticipated that the site will continue to meet its mitigation
goals over the course of the remaining monitoring period. Monitoring stakes will be pulled upon
satisfaction of the mitigation effort.
The next scheduled 36-month post-transplant monitoring is to occur in July 2011.
Eelgrass exposed along Sweetwater River within Silvergate frac-out transplant area and
surrounding reference area.
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2-Year Post-Transplant Eelgrass Survey
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REFERENCES
Merkel & Associates, Inc. 2008a. Eelgrass Restoration Plan Silvergate 138kV Horizontal
Directional Drilling (HDD) Frac-out at the Sweetwater River Marsh, Chula Vista, California.
Prepared for TRC Environmental Corporation. July 2008.
Merkel & Associates. 2008b. Post-Transplant Eelgrass Report for the SDG&E Silvergate 138 kV
Horizontal Directional Drilling Frac-out at the Sweetwater Marsh, Chula Vista, California.
Prepared for TRC Environmental Corporation. August 2008.
Merkel & Associates, Inc. 2008c. 3-month Post-Transplant Eelgrass Report for the SDG&E
Silvergate 138 kV Horizontal Directional Drilling Frac-out at the Sweetwater Marsh, Chula
Vista, California. Prepared for TRC Environmental Corporation. December 2008.
Merkel & Associates, Inc. 2009. 6-month Post-Transplant Eelgrass Report the SDG&E Silvergate
138 kV Horizontal Directional Drilling Frac-out at the Sweetwater Marsh, Chula Vista,
California. Prepared for TRC Environmental Corporation. January 2009.
Merkel & Associates, Inc. 2009. 1-Year Post-Transplant Eelgrass Report the SDG&E Silvergate
138 kV Horizontal Directional Drilling Frac-out at the Sweetwater Marsh, Chula Vista,
California. Prepared for TRC Environmental Corporation. July 2009.
National Marine Fisheries Service, Southwest Region, 1991. Southern California Eelgrass
Mitigation Policy (adopted July 31, 1991, rev. 11 August 30, 2005).
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APPENDIX A. MONITORING AND COMPLIANCE REPORTING SUMMARY
SOUTHERN CALIFORNIA EELGRASS MITIGATION POLICY
Monitoring and Compliance Reporting Summary
(to be submitted with each monitoring report)
PERMITTEE CONTACT INFORMATION:
Project Name (same as permit reference): Silvergate 138kV Horizontal Directional Drilling Frac-out
at the Sweetwater Marsh, Chula Vista, CA
PERMITTEE INFORMATION
Name
Contact Name
Phone
Email
SDG&E
Chris Terzich
858-637-3712
[email protected]
Address
City, State, Zip
Fax
8315 Century Park Ct
San Diego, CA 92123
858-637-3700
Address
City, State, Zip
Fax
5434 Ruffin Rd.
San Diego, CA 92123
858-560-7779
MITIGATION CONSULTANT
Name
Contact Name
Phone
Email
Merkel & Associates, Inc.
Keith Merkel
858-560-5464
[email protected]
PERMIT DATA:
Permit
Issuance Date
Expiration Date
Agency Contact
ACOE: Permit # 200601820-LAM
December 2006
Robert Smith
CDP:CCC Permit # 6-06-140
June 2007
Toni Ross
CDFG: Permit # 1600-2006-0328-R5
August 2007
Kelly Fisher
CRWQCB: Permit # 06C-077
October 2006
Chris Means
EELGRASS IMPACT AND MITIGATION REQUIREMENTS SUMMARY:
Permitted Eelgrass Impact Estimate (m2):
99.6
Actual Eelgrass Impact (m2):
99.6
On (post-construction date):
Eelgrass Mitigation Requirement (m2):
99.6
Mitigation Plan
Reference:
Impact Site Location:
Sweetwater Marsh, Chula Vista, California
Impact Site Center Coordinates (projection & datum):
LAT/LONG: 32040’33.26”N/117010’07.54”W
Mitigation Site Location:
Sweetwater Marsh, Chula Vista, California
Mitigation Site Center Coordinates (projection & datum):
LAT/LONG: 32040’49.06”N/117010’30.79”W
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October
2007
Merkel & Associates,
July 2008
2-Year Post-Transplant Eelgrass Survey
August 2010
PROJECT ACTIVITY DATA:
Activity
Start Date
End Date
Reference Information
Eelgrass Impact
October 16, 2007
October 16, 2007
Merkel & Associates, July 2008
Installation of Eelgrass Mitigation
July 24, 2008
July 24, 2008
Merkel & Associates, August 2008
Initiation of Mitigation Monitoring
October 2008
July 2013
Merkel & Associates, November
2008
Month
MITIGATION STATUS DATA:
Mitigation
Milestone
Scheduled
Survey
Survey Date
Area
(m2)
Density
(turions/m2)
Reference Information
0
3
6
12
24
36
48
60
July 2008
October 2008
January 2009
July 2009
July 2010
July 2011
July 2012
July 2013
July 24, 2008
September 20, 2008
January 9, 2009
July 24, 2009
August 11, 2010
TBA
TBA
TBA
99.6
94
99.6
96
NA
NA
NA
NA
69.1 ± 73.5
150.5 ± 72.5
230.4 ± 87.4
531.2 ± 224.5
851.2 ± 212.0
N
NA
NA
Merkel & Associates, August 2008
Merkel & Associates, November 2008
Merkel & Associates, January 2009
Merkel & Associates, July 2009
Merkel & Associates, August 2010
NA
NA
NA
FINAL ASSESSMENT:
Was mitigation met?
Not Applicable
Were mitigation and monitoring performed
timely?
Yes (to date)
Was delay penalty required or were supplemental
mitigation programs necessary?
None (to date)
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