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Historic Surface/Subsurface Conditions
Source: Geotechnical And Environmental Evaluation, Final Report Volume III, February 12, 2003, pg. 12
More Surface Condition Maps
Source: Geotechnical And Environmental Evaluation, Final Report Volume III, February 12, 2003, pgs. 18, 20, 21
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The geologic and human history of the formation and development
of the project site has shaped and defined the geotechnical and
environmental considerations for development of the project site.
As noted in the geotechnical report (Volume III), considerable
investigation work has been done, and that data, combined with
the history of the site and the current state of practice, indicates
the following (note figure numbers refer to figures in Volume
III):
 Download the Geotechnical
and Environmental Evaluation, Final Report Volume III, February
12, 2003
- Most of the site was an estuary, the delta of the Dominguez
channel behind the barrier sand spit, Rattlesnake Island. Most
of the project area was below sea level with the shoreline cutting
across the northwestern portion of the site; some of the site
was a marsh as shown on Figure 3. The estuary deposits consisted
of soft weak and compressible fine-grained soils (silts and
clays) and sands.
- The site, like most of southern California, will be subject
to strong ground shaking during major earthquakes. The site
is not within any fault special studies zones so the risk of
fault rupture is considered low. Loose sands have the potential
to liquefy during strong earthquakes. The westerly and southwesterly
portions of the site are mapped as potentially liquefiable on
the seismic hazards maps as shown on Figure 10. Current codes
require that liquefaction be addressed and mitigated for new
occupied building construction.
- Initial development consisted of constructing a railroad roughly
along the shoreline, followed by filling the estuary and marsh
using some dry land fill, but mostly material dredged as part
of the reclamation of the marsh and channel development of the
Port of Los Angeles. This eventually resulted in reclaimed land
over the project area up to approximately 15 feet above sea
level. The resulting fill depths range from less than five feet
near the northwest corner of the site to over 25 and 15 feet
in the southwesterly and southeasterly portions of the site,
respectively as shown on Figure 11. Except for recently placed
fills for new building construction, all of the fills should
be assumed to be uncertified and not acceptable for foundation
support under current codes.
- The area was a major oil field with approximately 115 oil
wells in the project area as shown on Figure 5. Nineteen wells
are still active (May 2002). The remaining wells were abandoned
or converted to water injection wells.
- Oil field development resulted in areal subsidence of as much
as 29 feet in the Long Beach harbor area, with subsidence in
the project area of 2 to 6 feet as shown on Figure 6. To arrest
the subsidence, water has been continuously injected into the
underlying formations. Recent (2000, 2001) subsidence monitoring
data shows that the subsidence in the project area has essentially
been stopped.
- Domestic groundwater pumping from the inland aquifers has
resulted in drawing the aquifers down below sea level resulting
in salt water intrusion from the sea. This intrusion is being
controlled by lines of fresh water injection wells that result
in interconnected fresh water mounds, which form a continuous
barrier to the salt water intrusion. Such a barrier extends
across a portion of the site as shown on Figure 9. Water injection
along the barrier creates a continuous flow of groundwater from
the barrier alignment towards the north, where the water table
declines in elevation. Water table elevations beneath the project
area range from sea level beneath the southern half of the WIP
area to 10 to 12 feet below sea level along the northern margin.
The depth to groundwater beneath the project area ranges from
approximately 8 to 20 feet across the site deepening from south
to north. The groundwater beneath the site is not used as a
potable aquifer.
- Much of the near-surface soil in the project area has been
contaminated from oil field operations. Other contamination
has occurred from land uses such as junk and maintenance yards.
In general the contamination is expected to be in the near-surface
soils.
Based on the geotechnical and contamination conditions, and the
current codes, the development of the site will have to consider
the following:
- Groundwater:
- The Water Replenishment District of Southern California
(WRD) manages the adjudication of the basin and supplies
water to LA County DPW for injection in the sea water intrusion
barriers. Groundwater activities are strictly controlled,
and an approval process is required for remedial activities.
While WRD is interested in cleanup of contamination, they
have the power to grant waivers for groundwater cleanups
required by Regional Water Quality Control Board (RWQCB).
- The property owner is typically responsible for contamination.
If investigation finds groundwater contamination requiring
remediation, it would probably be best treated as an area
wide problem rather than parcel-specific.
- There should be an area-wide shallow groundwater investigation
by the CRA to get a more clear perspective on the issue.
- Some cleanup of the upper soils should be anticipated throughout
the development area. In general the depth of contaminated soils
should be less than 5 to 10 feet, and cleanup could generally
be achieved by removal and replacement. It might be possible
to obtain a waiver of cleanup in event the contaminated soil
is not disturbed, and surface paving or encapsulation mitigates
the potential for offsite migration.
- There is potential for gas emission beneath new buildings
because of the oil field. Site specific monitoring can check
this, and some buildings might require under-building gas ventilation.
There are standard code provisions for such ventilation. Generally,
construction of a building over or adjacent to a former well
is not advisable and may not be allowed.
- Existing uncertified fill will not be suitable for foundation
support. Where fills are shallow (less than 10 feet) they
could
be removed and recompacted. I t should be noted that removal
of the fill could be difficult because some of the dredged
fill
material and the underlying estuary soils have been found to
be too soft and weak to support heavy grading equipment. Where
the fill is too deep for removal, pile foundations that gain
support below the fills and the soft underlying soils will
be
required. For intermediate depth fills (5 to 10 feet), methods
are available to improve them in place; however these will
require
requests for modifications to the City of Los Angeles requirements
which will delay permitting and which might not be approved
since they have not been used in the City before. Generalized
interpretations of the zones of fill depth are shown on Figure
12.
- Areas that are potentially subject to liquefaction require
investigation and, if liquefaction threat is confirmed, mitigation.
Liquefaction mitigation in the City has typically taken the
form of pile foundations. However improving the ground using
stone columns and other methods to mitigate the liquefaction
potential could be applicable. A generalized interpretation
of the zones of potential liquefaction is shown on Figure 12.
Source: Wilmington Industrial Park Economic Adjustment
Strategy, Final Report, February 12, 2003, pgs. 9-11
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