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.o, <br /> San Joaquin County DIRECTOR <br /> Donna Heran,REHS <br /> Environmental Health Department ASSISTANT DIRECTOR <br /> 600 East Main Street Laurie Cotulla, REHS <br /> uta Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> J_{S511C_ :.• __ Mike Huggins,REHS,RDI <br /> Cq tvl Website: www.s ov.or /ehd Margaret Clelloo, REHS <br /> �l F O R� 19 g Robert McCleon,REHS <br /> Phone: (209)468-3420 Jeff Carruesco,REHS,RDI <br /> Fax: (209)464-0138 Kasey Foley, REHS <br /> 23 February 2009 <br /> Harold & Dena Knowles <br /> C/O Law Office of Patrick D. Riddle <br /> 1811 Grand Canal Blvd Ste 2 <br /> Stockton CA 95207-8107 <br /> Subject: 102 S Wilson Way <br /> Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) has received and <br /> reviewed Fourth Quarter 2008 Groundwater Sampling Report (4thQR08), dated 11 <br /> December 2008, and has reviewed the data and interpretations in Third Quarter 2006 <br /> Groundwater Monitoring Report & Site Conceptual Model (SCM), dated 12 February <br /> 2007, both prepared on your behalf by Ground Zero Analysis, Inc. (GZA) for the above <br /> referenced site. <br /> The SCM characterizes the three local unauthorized releases from underground storage <br /> tank (UST) systems on the subject site, on the site at 101 S. Wilson Way, referred to <br /> herein as the Top Filling site, and the site at 130 S. Wilson Way, referred to as the Arco <br /> site. The subject site plume is characterized by the presence of total petroleum <br /> hydrocarbons quantified as gasoline (TPH-g), benzene, toluene, ethylbenzene and total <br /> xylenes (BTEX) and 1,2-dichloroethane (1,2-DCA). The Arco site plume consists <br /> primarily of methyl tert-butyl ether (MTBE), while the Top Filling plume consists of all of <br /> these contaminants. <br /> The SCM provides isopach maps of sand occurring between 35 and 60 feet below <br /> surface grade (bsg) and between 60 and 80 feet bsg. The sand thickness patterns <br /> illustrate east-west trending sand units. Other maps in the SCM illustrating TPH-g, <br /> benzene, MTBE and 1,2-DCA concentrations show that the dissolved plume <br /> distributions reflect, but are not identical to, the sand units distribution. Together, with <br /> the eastward groundwater flow direction, the maps demonstrate the hydrogeologic <br /> control of lithology on contaminant migration. GZA estimated that 750 pounds of TPH-g <br /> impacted soil above groundwater and 15,000 pounds of TPH-g impacted soil in <br /> groundwater. <br /> In the 4thQR08, GZA concludes that the contaminant concentrations of the subject site <br /> plume were within the normal concentration range and that the plume was stable and <br /> declining in mass. Monitoring wells along the south and east property margins were <br /> Comment and Directive Letter 0209 <br />