1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 2: PROBLEM FORMULATION
The available screening benchmarks used to evaluate preliminary data in the Scoping
Assessment are presented in Table 2-12 (preliminary soil background concentrations),
Table 2-13 (sediment screening benchmarks), and Table 2-14 (surface water screening
benchmarks). These benchmarks were updated in EEC Report and, again, as necessary for
this ERA. Preliminary soil background values were discussed in the previous section.
The screening process used for this phase of the evaluation was limited to comparing the
maximum concentrations of chemicals detected in soil, sediment, and surface water that
were retained in the data evaluation process (Section 2.3.1) to the selected screening
benchmarks (Tables 2-9, 2-13, and 2-14).
The maximum detected soil concentration in each area or site activity (e.g., waste sumps,
pipelines, or service roads) was screened against the preliminary background
concentrations for inorganic chemicals and the identified sediment screening benchmarks
(Table 2-15). Soils were screened against sediment benchmarks because most of the site soils
will become flooded as a result of proposed site restoration activities. Chemicals that
exceeded either background values or the sediment screening benchmarks were identified
as COPECs for the ERA. Chemicals that did not have an available benchmark were also
retained for further evaluation in the ERA.
The maximum detected sediment concentration in each area was screened against
preliminary background values and sediment benchmarks (Table 2-16). Chemicals that
exceeded either background values or the sediment screening benchmarks were identified
as COPECs for the ERA. Chemicals that did not have an available benchmark were also
retained for further evaluation in the ERA.
The maximum detected surface water concentration in each area or site activity was
screened against the selected surface water benchmark for chronic exposure (Table 2-17).
Chemicals that exceeded the surface water screening benchmark were identified as COPECs
for the ERA. Chemicals that did not have an available benchmark were also retained for
further evaluation in the ERA.
The COPECs identified in the Scoping Assessment (CH2M HILL, 1998b) for further
evaluation are presented by area for soil (Table 2-18), sediment (Table 2-19), and surface
water (Table 2-20). These COPECs, along with any others identified based on the ERA and
focused sampling efforts, were further evaluated in this ERA (Section 3).
2.4 Assessment Endpoints and Measures
The overall objective of the Problem Formulation is to describe ecological characteristics
of the Bolsa Chica Lowlands, summarize previously existing data, compare contaminant
concentrations to readily available screening benchmarks, and thereby assess whether
ecological risks may exist. To meet this objective, potential ecological effects of the site
contaminants important to decision making must be identified. Assessment endpoints
and measures relevant to ecological resources in the Lowlands are defined in this section.
SAC/143368(002.DOC) 2-11 ERA REPORT
7/31/02