Site Elevation, Groundwater, Sea Level Rise, and Flooding Information On Record
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Site Elevation
Final Environmental Impact
Report (EIR)
Project Description
Section B.4.1,
Page B-15
Existing elevations on the proposed site range from approximately 7 feet to 17 feet
above mean sea level (amsl).
Final EIR
Project Description
Section B.4.1,
Page B-15
Site topography consists of a flat, previously disturbed pad with a mild slope to the
west and north. Additionally, an on-site, man-made berm—ranging in elevation from
approximately 14 feet to 16 feet amsl—is located along the southern and western ends
of the property, adjacent to a fence that bounds the property (see Figure B-4). There is
an additional man-made berm in the west-central portion of the site that ranges in
elevation from approximately 21 to 23 feet amsl and served as the containment basin
located around the former LNG site storage tanks, enclosing approximately 11 acres of
the LNG site.
Final EIR
Project Description
Section B.6.2,
Page B-48
An estimated 120,000 CY of fill would be required to raise the substation site to the
proposed elevation, which ranges from approximately 16 to 21 feet amsl.
Final EIR
Aesthetics
Section D.2.3.3,
Page D.2-32
While the Bay Boulevard Substation would represent noticeable visible change in the
area, the change would be relatively consistent with the industrial character of the
project area, which includes the existing SBPP and South Bay Substation. Substation
support structures and equipment would be smaller in scale than existing transmission
structures, and the vertical lines associated with these components would be similar to
the linear orientation of existing transmission structures.
Final EIR
Climate Change
Section D.17.3.3,
Page D.17-19
The Proposed Project would include elevated pad construction with a graded elevation
of 16 to 21 feet above mean sea level (SDG&E 2010b).
San Diego Gas & Electric Company
South Bay Substation Relocation Project
March 2014
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Proponent’s Environmental
Assessment (PEA)
Project Description
Section 3.0.1,
Page 3-2
Existing elevations on the proposed site range from approximately 10 feet to 17 feet
above mean sea level (MSL). The site is mostly flat with a mild slope to the west and
north. A man-made berm—ranging in elevation from approximately 14 feet to 16 feet
above MSL—is located along the southern and western ends of the property, adjacent
to the existing fence. This berm inhibits the natural drainage pattern of the site.
Additional portions of the site are elevated as a result of a man-made containment
berm that ranges in elevation from approximately 21 feet to 23 feet above MSL.
PEA
Project Description
Section 3.6.5,
Page 3-51
An estimated 120,000 CY of Structural Fill would be required to raise the substation
site to the conceptual design elevation, which ranges from approximately 16 to 21 feet
above MSL.
Section 4, Page 4
Groundwater was encountered in all borings at the depths between 5 and 13 ½ feet
below the existing grade, corresponding elevations between 2 and 5 ½feet MSL with
an average elevation of 4 feet MSL. These groundwater level readings were taken
directly at the end of several days drilling operations when the boreholes had been
open for one to three days. These readings represent a relatively stable groundwater
condition at the time of field investigation and are considered more reliable as
compared with the estimated data from CPT soundings.
Groundwater Table
Geotechnical Investigation;
July 20, 2007
Groundwater could have a significant influence on construction operations depending
on finished floor elevation, utility invert elevation, and excavation depths. Bottom
stabilization and/or dewatering will likely be necessary for excavations below
approximately 5 ½ feet MSL. In addition, proper surface drainage of irrigation and
rainwater will be critical to the future performance of the project.
Geotechnical Investigation;
July 20, 2007
March 2014
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Section 6, Page 9
6.1.3 Groundwater was encountered between Elevations 2 and 5 ½feet MSL.
Groundwater could have a significant influence on construction operations. Excavation
bottom stabilization with a geo- and crushed rock blanket and/or dewatering using a
wellpoint system will likely be necessary for excavations below approximately 5 ½
feet MSL.
San Diego Gas & Electric Company
South Bay Substation Relocation Project
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Geotechnical Investigation;
July 20, 2007
Section 6, Page 9
6.1.3 Groundwater was encountered between Elevations 2 and 5 ½feet MSL.
Groundwater could have a significant influence on construction operations. Excavation
bottom stabilization with a geo- and crushed rock blanket and/or dewatering using a
wellpoint system will likely be necessary for excavations below approximately 5 ½
feet MSL.
Geotechnical Investigation;
July 20, 2007
Section 6, Page 9
6.1.3 Groundwater was encountered between Elevations 2 and 5 ½feet MSL.
Groundwater could have a significant influence on construction operations. Excavation
bottom stabilization with a geo- and crushed rock blanket and/or dewatering using a
wellpoint system will likely be necessary for excavations below approximately 5 ½
feet MSL.
Geotechnical Investigation;
June 8, 2011
Section 4, Page 5
Groundwater was encountered in all borings at the depths between 5 and 13 ½ feet
below the existing grade, corresponding elevations between 0.7 and 6.2 feet MSL with
an average elevation of 3.5 feet MSL. These groundwater level readings were taken
directly at the end of several days drilling operations when the boreholes had been
open for one to three days. These readings represent a relatively stable groundwater
condition at the time of field investigation and are considered more reliable as
compared with the estimated data from CPT soundings.
Groundwater could have a significant influence on construction operations depending
on finished floor and grade elevation, utility invert elevation, and excavation depths.
Construction of the proposed improvements may be significantly less difficult if
performed during the dry season. Bottom stabilization and/or dewatering will likely be
necessary for excavations below approximately 6 feet MSL. In addition, adequate
surface drainage of irrigation and rainwater will be critical to the future performance of
the project. The groundwater levels at the site are expected to fluctuate slightly (less
than 2 feet) with the tide of San Diego Bay and the water level in the adjacent salt
evaporation pond.
Geotechnical Investigation;
June 8, 2011
Section 6, Page 10
San Diego Gas & Electric Company
South Bay Substation Relocation Project
6.1.6 Groundwater was encountered between Elevations 0.7 and 6.2 feet MSL.
Groundwater could have a significant influence on construction operations. Excavation
bottom stabilization with a geo-fabric (Nicolon HS600 or equivalent) and crushed rock
blanket and/or dewatering using a wellpoint system will likely be necessary for
excavations below approximately 6 feet MSL.
March 2014
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Geotechnical Investigation;
June 8, 2011
Section 6, Page 12
6.3.7 In general, the soils generated during on-site excavations are suitable for reuse a
fill, provided they are free of vegetation, debris, and other deleterious matter. Due to
the proximity of groundwater and resultant high in-situ moisture content, excavated
soil may require significant moisture conditioning prior to reuse as fill. Soils with an
Expansion Index greater than 50 should be kept at least 4 feet below finish grades in
areas of the structural fill or in nonstructural fill areas outside of the substation pad
footprint. All over size materials greater than 6 inches should be buried at least six feet
below finished grade in accordance with SDG&E typical substation grading standard.
Geotechnical Investigation;
June 8, 2011
Section 6, Page 17
6.7.6 For large drilled pier such as used for transmission structures, vertical PVC tubes
(Schedule 40 with a nominal inside diameter of 2 inches) should be installed along
with reinforcing steel cages to allow for integrity testing in the event that significant
problems are encountered during pier construction below groundwater. The test
methods may include nondestructive testing with sonic and/or gamma-gamma logging.
Inspection tubes should be installed around the pile at a uniform spacing not exceeding
33 inches measured along the circle passing through the centers of inspection tubes. At
least 2 tubes should be installed per pile.
Geotechnical Investigation;
June 8, 2011
Section 6, Page 29
6.18.4 …Groundwater was encountered at approximate 10 feet below the existing
grade in the areas planned to receive new steel cable poles. Sloughing or reveling could
occur where relatively clean sands are encountered below groundwater level. Casing
and/or wet methods will be necessary for the construction of proposed pole locations.
PEA
Hydrology,
Section 4.8-2,
Page 4.8-7
The site is located between a fluvial dominated riverine system upstream and a tidally
dominated estuarine system downstream. Groundwater depths range between five and
13.5 feet below the existing grade based on recent test borings. Groundwater levels
within the Proposed Project area are considered to be relatively stable, but groundwater
depths may increase slightly during the summer dry months. The groundwater levels
within the Proposed Project area can fluctuate slightly (generally less than one foot)
with the tide of San Diego Bay and the water level in the adjacent salt marsh and
wetland.
March 2014
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San Diego Gas & Electric Company
South Bay Substation Relocation Project
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PEA
Final EIR
Section/Page #
Hydrology,
Section 4.8-2,
Page 4.8-11 to 12
Hydrology and Water
Quality
Section D.9.1,
Page D.9-2
San Diego Gas & Electric Company
South Bay Substation Relocation Project
Document Text
230 kV Loop-in, 69 kV Relocation, 138 kV Extension, and the South Bay Substation
Demolition
Impacts to groundwater supplies and recharge for the 230 kV loop-in, 69 kV
relocation, 138 kV extension, and the South Bay Substation demolition would be
similar to that identified for the construction of the Bay Boulevard Substation;
however, given that the groundwater is relatively shallow in the Proposed Project area
and trenching and foundation hole drilling would be required, there is the potential to
encounter groundwater during construction of these components. Trenches would be
excavated to a depth of approximately three to six feet, wood pole foundation holes
would be excavated to a depth of approximately eight to 12 feet, and steel pole
foundation holes would be excavated to a depth of approximately 20 to 45 feet. Where
localized shallow groundwater is encountered, dewatering systems, as outlined in
SDG&E’s BMP Manual, may be used to dispose of groundwater. Typically,
groundwater would be pumped into frac tanks and either discharged to land in
accordance with RWQCB regulations or transported to a nearby sewer inlet with
approval from the local wastewater treatment facility owner. In either case, the amount
of groundwater withdrawal is expected to be negligible and not have any effect on
existing groundwater supplies. Demolition of the South Bay Substation would
increase the amount of pervious surfaces at the existing substation site. The existing
South Bay Substation currently contains 5.7 percent impervious surfaces. All of the
impervious surfaces at the existing South Bay Substation site would be removed from
within the fenced facility during construction. Therefore, there would not be a
decrease in groundwater infiltration at the site. There would be a negligible increase in
permeable surfaces at the existing South Bay Substation site once the equipment pads
and foundations are removed. Therefore, impacts to groundwater supplies and
recharge from construction of transmission lines and demolition of the South Bay
Substation would be less than significant.
The depth to groundwater in the project area is between 5 and 13.5 feet. Groundwater
levels within the Proposed Project area are considered relatively stable, but
groundwater depths may increase slightly during the summer dry months. The
groundwater levels within the Proposed Project area can fluctuate slightly (generally
less than 1 foot) with the tide of San Diego Bay (SDG&E 2010a).
March 2014
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Final EIR
Hydrology and Water
Quality
Section D.9.3.3,
Page D.9-13
Due to the level of the groundwater in the project area (between 5 and 13.5 feet),
construction may require localized dewatering activities during the following activities:
trenching for underground duct bank utilities, removing concrete foundations
associated with steel poles, removal of concrete foundations at the South Bay
Substation, excavation activities associated with wood and steel pole foundations, and
excavations for the jack-and-bore operations. The construction activities would
typically occur at depths greater than 6 feet below grade, which would result in
groundwater being encountered during these activities since groundwater is known to
be present in the area between 5 and 13.5 feet below grade. Potentially significant
impacts could occur to nearby water resources if sediment-laden water is discharged
during excavation activities. Typically water produced by dewatering activities would
be placed in a dewatering system and would either be discharged to a sanitary sewer
system or in an upland location in accordance with San Diego RWQCB and the City’s
requirements. Mitigation Measures HYDRO-2a, HYDRO-2b, and HYDRO-2c include
measures to ensure dewatering activities would be completed consistent with local
dewatering requirements and would reduce impacts to a less-than-significant level
(Class II).
Final EIR
Geology and Soils,
Section D.7.1,
Page D.7-7
The Proposed Project site is located within a transitional hydrologic zone of the Otay
River watershed between a fluvial-dominated riverine system upstream and a tidally
dominated estuarine system downstream. The groundwater levels at the site are
expected to fluctuate slightly (less than 1 foot) with the tide in San Diego Bay and the
water level in the adjacent salt marsh and wetland (GEOCON 2007).
During field studies, groundwater was encountered in all borings at depths between 5
and 13 feet below the existing grade, corresponding to elevations between 2 and 5 feet
msl with an average elevation of 4 feet msl (GEOCON 2007). These groundwater level
readings were sampled at the end of drilling operation when the boreholes were
maintained open for one to three days. They indicate a relatively stable groundwater
condition at the time of the field investigation and are considered more reliable as
compared with the estimated data from cone penetration testing (CPT) soundings
(GEOCON 2007). Also see Section D.9, Hydrology and Water Quality, for a
discussion on groundwater.
March 2014
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San Diego Gas & Electric Company
South Bay Substation Relocation Project
Source Document
SDG&E’s Technical
Feasibility Review of Inland
Industries’ Proposed
Modifications to Project
(Exhibit 26 of CCC Staff
Report)
Section/Page #
Document Text
Page 4
Expanding the proposed substation by 6-10 acres also increases the technical and
environmental challenges of the Project. Site development is of particular concern at
this site because of the relatively high level of groundwater and existing soil
conditions. These challenges will require SDG&E to rework approximately 94,000
cubic yards of existing onsite soil during construction and import approximately
140,000 cubic yards of structural fill and Class-2 aggregate base material necessary to
raise the substation site to the final design elevations of the Project. This is necessary
due to drainage concerns, maintaining the majority of foundations, electrical vaults and
electrical duct packages above groundwater, and to mitigate risk of rising sea level.
Expanding the site would potentially result in 70,000 cubic yards or more of additional
fill material. If, for example, expansion would occur to the north, the site has not been
evaluated for drainage impacts, water retention, water-quality control issues, and the
requirement to demolish and remove the former LNG facilities and foundations. There
have been no environmental studies performed for this area, and there is potential
significant environmental impact with contamination and/or jurisdictional water issues.
It is unclear whether Inland has considered the significant cost impacts of expanding
the Project site by 6-10 acres.
Climate Change
Section D.17.3.3,
Page D.17-18 and
D.17-19
Potential adverse impacts of climate change include a rise in sea levels, which could
result in the potential displacement of coastal infrastructure and facilities. According to
the California Climate Change Center, a historical rate of sea level rise approaching 2
millimeters per year (0.08 inch per year) was recorded for California tide gages,
including San Diego, similar to the rate estimated for global mean sea level. Based on
research conducted for the CEC’s Public Interest Energy Research Program
Environmental Impact Report Climate Change Research Program, it is projected that
under medium to medium-high GHG emissions scenarios, mean sea level along the
California coast will rise from 1.0 to 1.4 meters (3 to 4.6 feet) by the year 2100
(California Climate Change Center 2009). Rising sea levels create additional risk for
flooding and an increase in the intensity of floods in areas that are already at risk, as
well as accelerated erosion and shoreline recession.
The National Oceanic and Atmospheric Association also regularly monitors and
predicts daily high and low tides for San Diego in addition to various coastal areas
throughout California. According to current 2010 data, a maximum high tide of 7.37
Sea Level Rise
Final EIR
San Diego Gas & Electric Company
South Bay Substation Relocation Project
March 2014
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feet is predicted for December 5, 2010, which represents the farthest date that can be
projected in terms of tidal activity (NOAA 2010). The Proposed Project would include
elevated pad construction with a graded elevation of 16 to 21 feet above mean sea level
(SDG&E 2010b).
Given the highest sea level rise prediction of 1.4 meters (4.6 feet) and maximum high
tide assumptions of 7.37 feet for the San Diego area, as well as the project pad
elevations designed for the Proposed Project, it is not anticipated that the Proposed
Project would experience an increase in exposure to adverse impacts associated with
sea level rise. The Bay Boulevard Substation would be built approximately 4 feet
above the projected sea level in 2100 considering the combined sea level rise of 4.6
feet and 7.37 feet of high tide, totaling approximately 12 feet. Accordingly, impacts
from this potential adverse effect of climate change, as identified in the 2009
California Climate Adaptation Strategy discussed previously, would be less than
significant (Class III).
Flooding
Final EIR
Hydrology and Water
Quality
Section D.9.1,
Page D.9-5 and Figure
D.9-1
The project area is not located within a 100-year flood zone. Linear components
associated with the 230 kV realignment, 138 kV extension, 69 kV realignment, and the
South Bay Substation demolition are located within the 500-year flood zone. Refer to
Figure D.9-1, Hydrology and Flood Zone Map, for the nearest flood zone.
Final EIR
Hydrology and Water
Quality
Section D.9.3.3,
Page D.9-15
Construction of the Proposed Project would remove the man-made berm on the LNG
site, and approximately 25% of pervious surfaces within the limits of the man-made
berm would be altered to that of impervious surfaces associated with the development
of the Bay Boulevard Substation. The substation pad site would be raised to establish a
higher elevation than the surrounding area with the central portion being the highest
point of elevation to direct flows to the perimeter of the substation site via a slope of
approximately 1%. The project proposes construction of a water quality basin along the
western limits of the Bay Boulevard Substation, as well as an engineered wetland to
the south. Runoff would be directed toward the water quality basin to direct the surface
runoff to the existing concrete-lined ditch at the northwest corner of the property.
Drainage basins have been designed to ensure stormwater flows will not exceed the
capacity of the storm drain system. Therefore, impacts would be less than significant
(Class III).
March 2014
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San Diego Gas & Electric Company
South Bay Substation Relocation Project
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Section/Page #
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Final EIR
Hydrology and Water
Quality
Section D.9.3.3,
Page D.9-15
Proposed Project facilities are not located within a 100-year flood hazard area.
Therefore, no new structures would be constructed that would impede or redirect flood
flow (Figure D.9-1, Hydrology and Flood Zone Map). As a result, the project would
not impact flood flows.
CPUC Data Request
Response #4
Question 2, Page 2
The revised grading plan meets all drainage and water quality requirements as
specified by the City of Chula Vista. Water Quality Basins B and C in the original
grading plan were intended to handle a large portion of the substation site runoff. The
revised grading plan directs nearly all of the site runoff to the westerly basin (Basin A),
resulting in approximately 10.5 acres of tributary area. A small portion of the
substation site discharges from the southeast corner to a point above the proposed
wetland. The site 100-year discharge to Basin A is approximately 35.3 cubic-feet-persecond. The 100-year discharge from Basin A to the existing southwest outfall is
approximately three cubic feet per second (in compliance with the City of Chula Vista
requirements). The proposed 100-year discharge at the southwest outfall, including all
drainage from Basin A and from the proposed wetland is in compliance with the
requirements of the City of Chula Vista.
San Diego Gas & Electric Company
South Bay Substation Relocation Project
March 2014
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