1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 4
Risk Characterization
The Risk Characterization is the final step in the ERA process whereby evidence linking
COPECs to potential adverse ecological effects in the Lowlands is evaluated using both
quantitative and qualitative methods. This evaluation is completed through the integration
of information gathered in the Problem formulation with the results of the Analysis – the
Exposure Characterization and the Ecological Effects Characterization – to establish a
“weight-of-evidence” for potential risk. For this ERA, the evidence evaluated consisted of
measured chemical concentrations in abiotic and biotic media, exposure estimates for birds
and mammals, results of site-specific toxicity bioassays and bioaccumulation studies for
aquatic organisms, and toxicity information obtained from the literature. In addition, the
proposed restoration plan for the different evaluation areas in the Lowlands was considered
in the overall assessment of risk potential to ecological receptors. The characterization of
risk is accomplished through three interrelated steps: risk estimation, risk description, and
uncertainty analysis. The final product is a listing of COECs for the Lowlands that will be
recommended for further evaluation or remedial action.
The identification of COECs through the Risk Characterization process is presented in
Figure 4-1. All COPECs that exceeded any available RTV as well as chemicals that showed
significant bioaccumulation in Nereis clam worms were retained as COECs. The overall risk
posed by a COEC in a given medium and evaluation area was determined based on the
types of RTVs that were exceeded (i.e., no-effect levels vs. low-effect levels and chronic
effect levels vs. acute effect levels). The overall risk categories were defined as follows:
• Unknown – RTVs were not available, so risk could not be quantified.
• None – Exposure does not exceed any of the available RTVs.
• Uncertain – Exposure exceeds a no-effect level, but risk could not be fully quantified
because a low-effect level was not available (Category U).
• Some Possible Risk – Exposure exceeds a no-effect level, but not a chronic low-effect
level (Category C).
• Possible Risk – Exposure exceeds a chronic low-effect level, but not an acute effect level
(Category B).
• Probable Risk – Exposure represents the highest level that could be quantified. Exposure
exceeds an acute effect level or showed significant bioaccumulation in Nereis clam
worms (Category A).
4.1 Risk Estimation
The risk estimation focuses primarily on quantitative methods to evaluate the potential for
risk. For this ERA, these included numerical estimates of risk, or hazard quotients (HQs),
and evaluation of site-specific toxicity bioassays and bioaccumulation studies.
SAC/143368(004.DOC) 4-1 ERA REPORT
7/31/02