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IWO t <br /> ATC Associates Inc. <br /> 6602 Owens Drive, Suite 100 <br /> Pleasanton, California 94588 <br /> Phone (925)460-5300 <br /> A s s o c I A T E s I N C . Fax(925)463-2559 <br /> www.atcassociates.com <br /> July 28, 2009G� C''l /-L1., -�_ <br /> � <br /> Ms. Victoria L. McCartney <br /> San Joaquin County JUL l 1 2009 <br /> Environmental Health Department <br /> 600 East Main Street ENVIRONNIENT HEALTH <br /> Stockton, California 95202-3029 PERMIU/SERVICES <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 /> 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 /> 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 nearsoil <br /> borings ATC-5 and SB-2 where methyl tertiary-butyl ether(MTBE)was detected at 39 micrograms per liter <br /> (Ng/L)at forty-two feet bgs, and 500 Ng/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 /> • Evaluation of the"horizontal'and"lateral"extent of impacted groundwater near the former <br /> underground storage tanks (USTs) (SB-5); and, <br /> • Evaluation of the potential for MTBE to migrate down gradient of the source area beneath <br /> Additional Investigation Workplan Addendum <br /> VU 3. 1 I Quik Stop No 132,July 28,2009 <br />