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1 <br /> wwcers oes�s consutir.wrs <br /> PHASE III SITE INVESTIGATION REPORT <br /> SAN JOAQUIN COUNTY HUMAN SERVICES AGENCY PROJECT <br /> 145 SOUTH SUTTER STREET <br /> STOCKTON, CALIFORNIA <br /> 1.0 INTRODUCTION <br /> This report presents the results of a soil and groundwater investigation performed by Roy F <br /> Weston, Inc (WESTON®) on behalf of the San Joaquin County Capitol Projects Division <br />' (Capitol Projects) and in response to requirements of the San Joaquin County Public Health <br /> Services Environmental Health Division (PHSEHD) The proposed work is based on field <br />' activities conducted between 10 July and 26 July 1995, and on data generated since work began <br /> in April 1988 The purpose of the July 1995 work was to evaluate the impact of petroleum <br /> hydrocarbons to soil and groundwater in the vicinity of a former UST cluster on the site. The <br />' location of the project site is shown on Figure 1 <br />' 2.0 BACKGROUND <br /> In April 1988, WESTON supervised the removal of nine underground storage tanks (USTs) from <br />' a former gasoline station located on the northwest corner of Washington and Sutter Streets. Soil <br /> samples collected from beneath the tanks indicated elevated petroleum hydrocarbons in soil <br />' Additional excavation and removal of approximately 2,000 cubic yards of soil was completed <br /> and the pit was backfilled with clean soil <br />' An initial soil and groundwater investigation (Phase I) was performed at the site by WESTON <br />' in late 1988, these results were presented in the Problem Assessment Report (PAR) entitled <br /> "Underground Fuel Storage Tank Site Investigation"dated February 20, 1989 Analytical results <br /> from this investigation indicated the presence of dissolved hydrocarbons in two of three monitor <br />' wells installed (MW-2 and MW-3), with the highest concentration present in MW-2 <br /> A Phase 11 groundwater investigation was completed in August 1991 which consisted of the <br /> installation of five additional monitor wells (MW-4 through MW-8), aquifer testing and a tidal <br />' influence study The results of this investigation indicated hydrocarbon concentrations were <br /> quantifiable in all five wells Subsequent quarterly groundwater monitoring results indicated the <br /> highest concentration of hydrocarbons alternating between downgradient monitor wells MW-7 <br />' and MW-8 <br /> • <br /> I <br /> LIPROJECrs\sANJoQ%HSAPtWE III 1 29 Autu"19" <br /> I <br />