1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 2:PROBLEM FORMULATION
background evaluations, Steffeck, et al. (1996), recommended the use of three samples from
the oil well sites that were collected 8 feet below ground surface (bgs) in an area with an
estimated 6 feet of fill (OW3, OW12, and OW13). It was assumed that these three samples
were not impacted by site activities (i.e., they lacked organic compound contamination) and
that they were representative of soil conditions within 2 feet of the “pre-filled” ground
surface. The results of the inorganic analyses for these three samples were averaged to
estimate preliminary background concentrations for inorganic chemicals in both soils and
sediments from the Bolsa Chica Lowlands (Table 2-12). The preliminary background values
were used for both soil and sediments, because most of the site will be flooded after
remediation. No background values were available for surface water.
Because of the limitations of this background evaluation and the ongoing sampling, results
of background comparisons for inorganic chemicals were not used as the basis for removing
a given chemical from the list of COPECs for the ERA.
2.3.3 Preliminary Evaluation of Chemical Contamination
The preliminary evaluation of chemical contamination during the Scoping Assessment
(CH2M HILL, 1998b) was limited to comparing site data to available screening benchmarks
for soil, sediment, and surface water.
Screening benchmarks for sediment and surface water were selected from available sources,
including toxicological databases, wildlife toxicological reviews, and scientific literature.
Sediment screening benchmarks were selected from U.S. EPA proposed values (U.S. EPA,
1993a, 1993b), U.S. EPA sediment quality criteria and benchmarks (U.S. EPA, 1996b), effects
range low (ER-L) values from Long et al. (1998) and Long and Morgan (1990), lowest effects
levels in the sediment toxicity database compiled by Jones et al. (1997), lowest effect levels
from the Ontario sediment quality guidelines (Persaud et al., 1993), threshold effects levels
from the Florida state sediment quality guidelines (MacDonald, 1994), and threshold effects
concentrations from the Assessment and Remediation of Contaminated Sediment Project
(Jones, et al., 1997; U.S. EPA, 1996c). In addition, sediment screening benchmarks for
nonionic organic chemicals without other available benchmarks were derived using
equilibrium partitioning methodology (Jones et al., 1997). The sediment screening
benchmarks for Bolsa Chica (Table 2-13) were selected using the following hierarchy:
• U.S. EPA values
• Lowest available marine benchmark
• Lowest available freshwater benchmark
Screening benchmarks for aquatic organism exposure to surface water were selected from
marine Ambient Water Quality Criteria (AWQC), where available, and from California
enclosed bays and estuaries proposed criteria and lowest effect levels for marine organisms
(Table 2-14). The surface water benchmark was selected using the following hierarchy:
• Chronic marine ambient water quality criteria
• California enclosed bays and estuaries proposed chronic criteria
• Chronic lowest observed effect level
When a chronic value was not available, but an acute criterion was, the acute value was
divided by an acute-to-chronic factor of 10 to estimate a chronic value.
ERA REPORT 2-10 SAC/143368(002.DOC)
7/31/02