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I <br /> Treadve118rbb <br /> 7 November 2008 IR CIE RD <br /> Project: 2597.12 <br /> Ms. Vicky McCartney NOV 12 2008 <br /> Senior Registered Environmental Health Specialist ENVIRONMENT HEALTH <br /> San Joaquin County Environmental Health Department PERMIT/SERVICES <br /> 600 East Main Street <br /> Stockton, California 95202-3029 <br /> Subject: Addendum to Investigation Summary Report and Groundwater Monitoring Work Plan <br /> Form Counte�rr Motor Pool <br /> 130 North Hunter Street <br /> Stockton, California <br /> Dear Ms. McCartney: <br /> This addendum to our"Investigation Summary Report and Groundwater Monitoring Work Plan, Former <br /> County Motor Pool, 130 North Hunter Street, Stockton, California"(Work Plan) dated 24-March 2008 is in <br /> response to your letter dated 28 April 2008. 4 rebrv"J <br /> We have accepted your comments regarding additional laboratory analyses during quarterly events and <br /> during annual events. <br /> In your letter dated 28 April 2008, you suggest that a deep monitoring well should be installed in the <br /> vicinity of former monitoring wells MW-1, MW-2, and MW-3 and screened approximately seventy to — <br /> eighty-five feet below ground surface (bgs). In response, we first propose to first perform a soil <br /> boring to 85 feet bgs and collect a deep grab groundwater sample (Boring SB-10, see Figure 1). <br /> We propose to analyze this deep groundwater sample for Total Petroleum Hydrocarbons (TPH) as <br /> gasoline (TPH-g), benzene, toluene, ethyl benzene, and total xylenes (BTEX), methyl tert-butyl ether <br /> (MTBE), and 1,2-dichloroethane (1,2-DCA). <br /> The Work Plan describes the collection of groundwater samples by purging three casing volumes. <br /> We believe that conducting low flow purging and sampling techniques as described by the EPA' are a - <br /> more appropriate method and propose to use this method for groundwater sampling. <br /> Please provide an approval of this addendum with any comments that you have. Please contact us if you <br /> have any questions. <br /> Sincerely, <br /> TREADWELL& ROLLO, INC. <br /> 1 r <br /> Michael D. Chendorain, REA David G. Dixon, PG <br /> Senior Project Scientist Senior Associate <br /> 25971205.MDC <br /> Attachment <br /> ' R. W. Puls, M.J. Barcelona. 1996. Low-Flow (Minimal Drawdown) Ground-Water Sampling Procedures. <br /> EPA/540/S-95/504,April 1996. <br /> ENVIRONMENTAL AND GEOTECHNICAL CONSULTANTS <br /> 555 MONTGOMERY STREET, SUITE 1300 SAN FRANCISCO CALIFORNIA 94111 T 415 955 9040 F 415 955 9041 www.treadwellrollo.com <br />