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URS <br /> 1E <br /> D Eav <br /> September 29, 2003T - 3 2003 <br /> dC <br /> ENVIRONMU4� 1�'Lnl <br /> PERMI�ISERVICES <br /> Mr Mike Infurna, Senior REHS <br /> LOP/Site Mitigation Unit IV 6020 <br /> San Joaquin County Environmental Health Department 06 a4 <br /> 304 East Weber Avenue, Third Floor <br /> Stockton, California 95202 <br /> Re: Momtormg Well Installation, Site Conceptual Model,and <br /> Third Quarter 2003 Groundwater Monitoring Report <br /> ARCO Service Station#6020 <br /> 1711 East Yosemite Avenue,Manteca, California <br /> Dear Mr Infurna <br /> URS Corporation Americas (URS) on behalf of Atlantic Richfield Company (ARCO) is submitting this <br /> Monitoring Well Installation, Site Conceptual Model, and Third Quarter 2003 Groundwater Monitoring <br /> Report for ARCO Station No 6020 located at 1711 East Yosemite Avenue in Manteca,California The report <br /> was prepared to document the installation of three additional groundwater monitoring wells at the site as <br /> requested by the San Joaquin County Environmental Health Department(SJCEHD)in a letter dated April 2, <br /> 2003 (Attachment A) <br /> SITE BACKGROUND <br /> The site is located at 1711 East Yosemite Avenue in Manteca, California (Figure 1) The site is currently <br /> operating as a gasoline station Site structures include three double-walled fiberglass underground storage <br /> tanks (USTs) with associated piping, two dispenser islands, and a convenience store(Figure 2) <br /> 1n 1996, ARCO was granted case closure at this site by SJCEHD and subsequently destroyed four on-site <br /> groundwater monitoring wells (MW-1 through MW-4) <br /> Three gasoline USTs and associated product lines and dispensers were removed from the site in April of <br /> 1999 Petroleum hydrocarbon impacts to soil and groundwater were documented in the vicinity of the UST <br /> cavity during sampling activities associated with the removal of the USTs and product lines (Appendix B) <br /> The highest concentrations of gasoline-related compounds were reported in soil samples collected beneath the <br /> two dispenser islands Soils were over-excavated to a maximum depth of seven feet below ground surface <br /> (bgs)beneath the dispenser islands and 17 feet bgs beneath the former USTs Total petroleum hydrocarbons <br /> as gasoline (TPHg) and methyl tert-butyl ether(MtBE) were reported at maximum concentrations of 1,430 <br /> and 20 8 milligrams per kilogram(mg/kg),respectively, in post-excavation soil samples Additionally,MtBE <br /> was reported at a maximum concentration of 310 micrograms per liter(Ag/]L)from grab groundwater samples <br /> collected in the UST cavity Three new gasoline USTs were installed at the site in August of 2000 under the <br /> supervision of IT Corporation <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive Suite 300 <br /> Sacramento CA 95833 <br /> Tel 916 679 2000 <br /> Fax 916 679 2900 <br />