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SOIL AND GROUNDWATER INVESTIGATION 200 N. BECKMAN STREET LODI, CALIFORNIA 1.0 INTRODUCTION This report presents the results of a soil and groundwater investigation conducted by ROY F WESTON, INC (WESTON@) tar the San Joaquin County Mosquito and Vector Control Distnet i (SJCMVCD) facility at 200 North Beckman Street in Lodi, California (See Figure 1) The ' purpose of the investigation was to generate additional data to assist the San Joaquin County Public Health Services Environmental Health Division (EHD) in considering site closure j certification ' 1.1 Backeround In 1986, the SJCMVCD removed three underground storage tanks (USTs) from the site and excavated soil beneath the gasoline UST to a depth of 31 feet below grade A soil and groundwater investigation conducted by Weiss Associates on behalf of the SJCMVCD in 1987 consisted of soil borings and the installation of three groundwater monitor wells (MW-1, MW-2 and MW-3) to a depth of approximately 50 feet (see Figure 2) While the investigation identified the presence of hydrocarbon compounds in soil beneath the location of the former gasoline UST, no detectable hydrocarbon compound presence was found in the three groundwater monitor wells A low permeability soil layer at approximately 32 feet below the ground surface was believed to have acted as a barrier to downward migration of hydrocarbon compounds to groundwater The Weiss Associates study also concluded that, based on groundwater elevations in the three monitor wells, groundwater beneath the site flowed in a north-northeasterly direction In December 1991, ROY F WESTON, INC (WESTON@) began a quarterly groundwater monitoring program on behalf of the SJCMVCD WESTON's first sampling effort found that only one of the three monitor wells contained enough water to sample Consequently, the EHD requested that an additional monitor well be installed on the site northeast of the former tank area to evaluate the possible downgradient migration of hydrocarbons in groundwater The new well (MW-4) was installed in July 1992 according to the EHD-approved WESTON work plan A detailed description of the well installation and sampling activities was presented in the ' WESTON report entitled Well Installation and Quarterly Groundwater Monitoring Report, dated October 14, 1992 Analysis of the samples from the initial sampling of the new well (MW-4) on August 25, 1992 showed total petroleum hydrocarbons-gasoline fraction (TPH-G) and benzene, toluene, ethylbenzene and xylenes (BTEX) to be non-detectable Furthermore, all groundwater sampling events conducted after August 1992 (November 1992 and January 1993) have shown non- detectable results for TPH-G and BTEX in the new monitor well and any other wells containing sufficient water to sample ,rk\RPrskv(mvc m wN 1 axr_sa,