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wall'i <br /> l <br /> Mul <br /> ON <br /> WE <br /> I , <br /> Clayton <br /> (-%%fil lA71;i�, <br /> Cfl\51.[iS\I: <br /> Executive Summa <br /> Clayton Environmental Consultants, Inc., was retained by Orchard Supply Hardware (OSH) <br /> to summarize the results of soil and groundwater investigations and soil remediation <br /> conducted at the northeast corner of MacArthur Drive and Grant Line Road in Tracy, <br /> California (Figure 1). <br /> Since January 1990, Clayton has completed the following work at the site: <br /> 1. Phase I environmental assessment of approximately 40-acre vacant parcel <br /> 2. Installation of three monitoring wells (MW-1, MW-2, and MW-3) and sampling and <br /> ` analysis of soil and groundwater <br /> 3. Excavation and aeration of 1,650 cubic yards of soil in the vicinity of a former fuel <br /> pump island and septic tank near the southwest corner of the property <br /> 4. Installation of an additional monitoring well (MW-3B) downgradient of the excavation <br /> and stimpling and analysis of soil and groundwater <br /> 5. Installation of five boreholes downgradient of the excavation and sampling and <br /> analysis of soil, sampling and analysis of groundwater from MW-3B <br /> Based on completion of the above tasks, Orchard Supply Hardware requested that San <br /> Joaquin County Public Health Services, Environmental Health Division (SJC/EHD) <br /> ' recommend site closure to the Central Valley Regional Water Quality Control Board <br /> (RWQCB). Ms. Laurie Cotulla, Program Manager for the SJC/EHD recommended site <br /> closure in a letter to Ms. Beth Thayer, Associate Engineer for the RWQCB, dated July 16, <br /> 1991. <br /> Ms. Thayer responded with several concerns about site closure,which were presented in a <br /> letter dated August 19, 1991. Ms, Thayer's concerns are listed in italics.below, brief- <br /> responses.to these concerns follow. The body of this report summarizes all work completed <br /> at iiic:site by Clavton. As requested by the RWQCB, our intention in preparing this report <br /> Ib was to consolidate and clarify reports, addendums, letters, and personal communication that <br /> transpired 'between Clayton and the SJC/EHD. <br /> f About the soil excavation in the-vicinity of the former fuelpumpisland and septic tank, Ms. - <br /> i , Thayer states: <br /> "Contaminants in five soil samples ranged from 60 ppm to 1100 ppm oil and grease <br /> hydrocarbons. Apparently, additional lateral excavation (over-excavation) occurred towards <br /> the northeast. However, it is unclearfrom either the re ort or the addendum� h' p alum whether the <br /> i excavation was extended vertically below 10.5 feet." <br /> Orchard Supply must present a precise description of the.over-excavation activities before <br /> closure may be considered, including the fallowing information: <br /> { <br /> 3 1. Total depth of excavation below sanmples V 1, NW-1, MN-1, NE-1, and ME-1; <br /> E, <br /> L. <br /> E <br />