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ATC Associates Inc. <br /> (M%TC6602 Owens Drive, Suite 100 <br /> Pleasanton, California 94588 <br /> Phone(925)460-5300 <br /> Ass o c l ATE s I N C . Fax(925)463-2559 <br /> www.atcassociates.com <br /> July 28, 2009 <br /> Ms. Victoria L. McCartney <br /> San Joaquin County <br /> Environmental Health Department <br /> 600 East Main Street <br /> �. Stockton, California 95202-3029 <br /> Reference: Additional Investigation Workplan -Addendum <br /> Quik Stop Market No. 132 <br /> 3555 West Hammer Lane <br /> Stockton,California <br /> ATC Project Number: 75.62503.3206 <br /> r Dear Ms. McCartney: <br /> ATC Associates Inc.(ATC)is pleased to present this addendum to our Additional Investigation Workplan, <br /> dated May 18, 2009, to perform an additional subsurface investigation at Quik Stop Market No. 132, <br /> located at 3555 West Hammer Lane in Stockton, California (Site). The purpose of this addendum is to <br /> address comments regarding the Workplan provided in correspondence from the San Joaquin County <br /> i. Environmental Health Department(SJCEHD)dated June 5, 2009. <br /> The Workplan was submitted in response to correspondence dated September 23, 2008, from the <br /> SJCEHD directing the following:assess the lateral extent of petroleum hydrocarbon contamination in the <br /> first water-bearing zone identified by the SJCEHD to be approximately five to ten feet below ground <br /> surface(bgs);assess the vertical extent of petroleum hydrocarbon contamination in groundwater near soil <br /> L borings ATC-5 and SB-2 where methyl tertiary-butyl ether(MTBE)was detected at 39 micrograms per liter <br /> (ug/L)at forty-two feet bgs,and 500 pg/L at twenty-nine feet bgs, respectively;and assess the petroleum <br /> hydrocarbon contamination remaining in soil in the area of soil sample QS-2 collected at approximately ten <br /> feet bgs. <br /> In the May 18, 2009 Workplan,ATC proposed to advance three soil borings (SB-4, SB-5, and SB-6)to <br /> ` address soil and groundwater data gaps that include: <br /> Evaluation of impacted soil that may remain near the original release at the north end of <br /> the pump island (SB-4); <br /> L <br /> Y Evaluation of the"horizontal'and"lateral"extent of impacted groundwater near the former <br /> underground storage tanks (USTs)(SB-5);and, <br /> 'r • Evaluation of the potential for MTBE to migrate down gradient of the source area beneath <br /> r Y U Additional Inmagation Workplan Addatdum <br /> Quik Stop No.132,Stmklon,CA <br /> .....,..., ,... July 28,2009 <br /> i <br /> V <br />