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Mr. Aragon February 5, 2010 Page 2 study of the additives that were included in the tetra-ethyl lead mixture when added to gasoline was conducted. Tetra-ethyl lead mixtures included approximately 35% of 1,2- dibromoethane and 1,2-dichloroethane. The presence of these compounds in either Site soil or soil gas would be significant, because it would indicate that tetra-ethyl lead likely also is present. However, neither of these compounds was detected in either Site soil samples or soil gas samples. Soil detection limits for both compounds (1,2- dibromoethane and 1,2-dichloroethane) were less than 1 microgram per kilogram. As a result, we are confident that tetra-ethyl lead is not a compound of concern in Site soil or soil gas. It is anticipated that the approach for remediation of impacts identified at the Site will be excavation and off-site disposal; thus eliminating the potential source of on-site impacts, including tetra-ethyl lead. In light of the information provided above and including the anticipated remedial approach, if DTSC still considers tetra-ethyl lead to be of concern at the Site, this issue will be addressed through post remediation sampling. CLOSING We appreciate your review of the subject document and your comments. If the DTSC agrees with the handling of the comment as identified in the response above, the RI Report will be finalized and the Removal Action Workplan/Health Risk Assessment will be prepared for the Site. It is anticipated that the final RI Report will be submitted to the DTSC approximately 15 working days after receipt of the approval from DTSC accepting the response to the above identified comment. If you have any questions, please contact Ms. Melitta Rorty at (925) 415-6328 or myself at (626) 440-6067. With Regards, Parsons, Inc. )&_�' P. Thomas P. Blaney Project Manager cc: Melitta Rorty, PG&E Adrienne LaPierre, Iris Env. Paul Farmanian, Parsons