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IGEOCON CONSULTANTS,INC. GEOTECHNICAL ■ ENVIRONMENTAL ■ MATERIALS Project No. E8857-02-01 September 8,2016 San Joaquin County Environmental Health Department 1868 East Hazelton Avenue Stockton,California 95205-6232 Attention: Mr.Nuel Henderson Subject: RESPONSE TO SITE INVESTIGATION REPORT COMMENT LETTER FORMER CITY OF MANTECA POLICE FIRING RANGE Dear Mr. Henderson: We have prepared this letter to respond to the comments you provided in the Site Investigation Report Comment Letter, dated March 3, 2016. Please note that many of the comments are addressed in the recently submitted Remedial Action Plan, Former Police Firing Range, Manteca, California (RAP), prepared by Pacific Edge Engineering. A copy of the comment letter is attached,and the comments and responses are as follows: • Collect sufficient soil samples from the area mapped as less impacted than TCLP>5 mg/1 and analyze for lead, antimony, arsenic, and copper to better define the STLC>5 mg/1 contour and refine the California hazardous waste mass estimate. As outlined in RAP Section 5.1, Geocon will stake the limits of the areas where soil excavation(TCLP>5 mg/l and STLC>5 mg/1) is proposed. Confirmation testing of the limits prior to excavation will include soil sample analysis for lead, antimony, arsenic, and copper, and the use of hand-held x-ray fluorescence (XRF) device. In addition, as outlined in RAP Section 5.4, the remediation contractor will perform disposal profile sampling prior to excavation in accordance with the proposed disposal facility requirements for both the Federal (RCRA)and California hazardous waste streams. • Collect and analyze sufficient soil samples from areas outside the impacted area to establish site-specific background concentrations for lead,antimony,arsenic, and copper. In lieu of establishing background concentrations, residential land use screening criteria are proposed in the RAP as cleanup goals for the site. This should allow unrestricted land use once impacted soils have been removed. As outlined in RAP Section 4.0, the cleanup goals for the chemicals of potential concern (COPCs), with the exception of arsenic, are the May 2016 USEPA Regional Screening Levels (RSLs) for residential soil (Note that the correct cleanup goal for copper is 3,100 mg/kg, not 31,000 mg/kg as listed in the RAP). The RAP proposes a cleanup goal of 12 mg/kg for arsenic, which is consistent with the screening number that the Department of Toxic Substances Control (DTSC) Schools Program uses when evaluating arsenic at school sites. 6671 Briso Sheet 0 Livermore,CA 945502505 0 Telephone 925.3715900 0 Fax 925.371.5915