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p <br />" Tfreadw�eN&F DNO <br /> i <br /> 7 November 2008 � <br /> Project: 2597. 12 %C� T <br /> Ms, Vicky McCartney <br /> Senior Registered Environmental Health Specialist <br /> San Joaquin County Environmental Health Department <br /> 600 East Main Street <br /> Stockton, California 95202-3029 <br /> Subject: Addendum to Investigation Summary Report and Groundwater Monitoring Work Plan <br /> Form Counter Motor Pool <br /> 130 North Hunter Street <br /> Stockton, California <br /> I <br />:I 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. <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 rt rl <br /> boring to 85 feet bgs and collect a deep grab groundwater sample ( Boring SB-10, see Figure 1), S @, 1 <br /> We propose to analyze this deep groundwater sample for Total Petroleum Hydrocarbons (TPH) as ,'i, I , <br /> gasoline (TPH-g), benzene, toluene, ethyl benzene, and total xylenes (BTEX), methyl tert-butyl ether v ^I { <br /> (MTBE), and 1,2-dichloroethane (112-DCA). 6 „ <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 /> 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 />