SITE INFORMATION AND CORRESPONDENCE

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%0001 %../ HORIZON ENVIRONMENTAL INC. —.� Specialists in Site Assessment,Remedial Testing. Design and Operation June 30, 2009 Mr. Michael J. Infurna San Joaquin County 1 rivironnlental Health Department 600 East Main Street Stockton, California 95202-3029 Subject: Technical Justification for "No Further Action Required" Quik Stop Station No. 39 2285 bast Freemont Street, Stockton, California Mr. Infurna: At the request of Quik Stop Markets, Inc., .11orizon Environmental Inc. (Horizon) is responding to the San Joaquin County Environmental I-Icaltli Department (EI-ID) letter dated 13 May 2009 (enclosed). The letter contains l,'HD comments on the review of fidditionat Groundwaler Investigation arta Updated Site Coneelmiel jlfodel (Report) dated 14 April 2009. The EHD concurs with the Horizon conclusion that the residual petroleum hydrocarbon plunxe is stable and poses no risk to public health or beneficial use of groundwater. Th.e EFID requested a soil gas work plan or technical justification that addresses the risk and potentW exposure of the residual hydrocarbon impacts to public safety. Ilorizon proposes that a soil gas investigation is not necessary and presents below a discussion and vapor illtrusion evaluation in the form of a technical justification. Site Description and Baelcgrouiirl The Quik. Stop No. 39 site is a convenience market and retail gasoline station located on the northwestern Corner of the intersection of}Bast Frcmont Street and E Street in a commercial and residential area of Stockton, Califiornia as shown on Figure 1. Structures and installations at the site include a station building, gasoline dispenser islands under a canopy, and former and existing gasoline undergrOUnd storage tanks (USTs)as shown on figure 2. Two gasoline underground storage tank (UST) systems were removed in October 1998. Two soil samples were collected from depths of approximately 13 feet from beneath each UST and from depths of approximately 3 feet beneath the dispensers. With the exception of low concentrations of xylenes and tert-butanol in one UST sample, no gasoline constituents were detected in soil samples from the beneath the US`I's or MW-1 through MW-8 well borings. Total petroleum hydrocarbons as gasoline (TPlJg) and volatile aromatic compounds benzene, toluene, ethylbcnzene and xylenes (13TEX) were detected beneath the dispensers. Soil analytical data are summarized in Table I. Eight groundwater monitoring wells, MW-1 through MW-8 (screened across the water table), were installed at the subject site from 1999 to 2006. Soils encountered in borings to 4970 Windplay Drive,#C5 • EI Dorado Hills.CA 95762 • (916)939-2170 • FAX(916)939-202 P.O.Box 5283 • Bakersfield,CA 93388 + (661)589-8389 • FAX(661)589-1456