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' Meh+uEFS DESICaEliSLIMH1LfINSS SECTION 1.0 ' INTRODUCTION ' 1.1 SCOPE AND PURPOSE ' This Corrective Action Plan (CAP) presents the results of a feasibility study and evaluation of remedial action alternatives performed by Roy F. Weston, Inc (WESTON®) on behalf of the San Joaquin County Capital Projects Division (Capital Projects) and in response to requirements of the San Joaquin County Public Health Services Environmental Health Division (PHSEHD) for the Human Services Administration (HSA) building located at 145 South Sutter Street, Stockton, California. The purpose of the CAP is to provide an assessment of the impacts and, through an evaluation of potential alternatives, select a proposed action that will adequately protect human health, safety, and the environment and will restore or protect current ofr'potential beneficial uses of water The location of the project site is shown on Figure 1 ' 1.2 SITE HISTORY In April 1988, WESTON supervised the removal of nine underground storage tanks (UST's) from a former gasoline station located on the northwest corner of Washington and Sutter Streets. Petroleum hydrocarbons were detected in soil samples collected from beneath the tanks An initial soil and groundwater investigation (Phase I) was performed at the site by WESTON in late 1988 Dissolved hydrocarbons were detected in two of three monitor wells installed ' during this investigation (MW-2 and MW-3) The highest concentrations of petroleum hydrocarbons were detected in monitor well MW-2 In 1989 approximately 2,000 cubic yards of fuel hydrocarbon contaminated soils and one additional fuel storage tank were excavated and disposed of off site (WESTON, 1989b) Soil was excavated until groundwater was encountered (approximately 29 feet below ground surface ' (bgs)) Confirmation sampling of the side walls of the excavation was performed and verified that the target cleanup levels (10 mg/kg of total petroleum hydrocarbon residues) were met except for one area Soil samples taken from south west of the excavation indicated that a ' limited volume of soil in excess of the target level remained but could not be removed because of site constraints ' A Phase II groundwater investigation was completed in August 1991 which consisted of the installation of five additional monitor wells (MW-4 through MW-8), aquifer testing, and a tidal ' influence study However, no product layer (free phase) of fuel hydrocarbons was observed on the water table in any of the wells During this investigation, dissolved hydrocarbons were detected in all five new monitor wells Subsequent quarterly groundwater monitoring results ' indicated that the highest concentrations of dissolved hydrocarbons were present in downgradient monitor well MW-8, which is located near underground tanks owned by the City of Stockton i ' LTROJECTszANfOQ\HSMACP[ONPL L