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, EPA Comments Response to Comments and the Draft Final Remedial Action Report for SWMUs 2,3, and 33 for DDJC-Tracy April 2002 GENERAL COMMENTS 1. The response and revised RAR does not appear to address General Comment 1. The first sentence of the response states that the original clean up level could possibly be attained but that the clean up is not warranted and the deletion of the cleanup goal for the sum of DDD, DDE, and DDT(DDX) has been approved by Remedial Project Managers and formalized in the final explanation of significant differences (ESD) (URS,2001). However, based on the responses provided, it is still unclear why the exposure assumptions that were considered appropriate at the time the record of decision (ROD) was written, were then subsequently considered 'overly protective". For example, it is indicated that the estimation of risk to killdeer was adjusted since killdeer are the only species likely to spend most of their lives at solid waste management units (SWMUs)2 and 3, and would more likely ingest flying insects as 75% of its diet. Thus, the original assumption of 100% earthworms in the ROD is "incorrect." However, 100% ingestion of the most contaminated food item (e.g., earthworms) is used for the worst case exposure assumption in all U.S. EPA ecological risk assessments, and U.S. EPA considers it an acceptable, conservative estimate of upper-bound or worst case scenarios. Thus, the text should not indicate that the assumption is incorrect. Please revise the text to indicate that receptor-specific and site- specific assumptions were refined in order to represent less conservative exposure conditions, which were agreed to by risk managers to be more representative of potential exposures at this site. The response to General.Comment I also indicates that"Site specific bioaccumulation factors (BAFs) are more appropriate for decisions related to cleanup levels." However, it is not evident that the Defense Logistics Agency(DLA)re-examined or updated any of the other exposure assumptions used in the Ecological Risk Assessment, or collected additional site-specific data to support changing the cleanup goals. The proposed revised text mentions that the use of site- specific BAFs is more appropriate for decisions. However, it remains unclear whether additional site-specific data were gathered in order to develop more specific exposure estimates. Please revise the RAR text to indicate that data were collected in order to support site-specific BAFs to support the adjustment of the environmental risk assessment assumptions and the decision to eliminate DDX from the ROD. 1