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SOIL AND GROUNDWATER INVESTIGATION <br /> 200 N. BECKMAN STREET <br /> LODI, CALIFORNIA <br /> 1.0 INTRODUCTION <br /> This report presents the results of a soil and groundwater investigation conducted by ROY F <br /> WESTON, INC (WESTON(v) for the San Joaquin County Mosquito and Vector Control District <br /> (SJCMVCD) facility at 200 North Beckman Street in Lodi, California (See Figure 1) The <br /> purpose of the investigation was to generate additional data to assist the San Joaquin County <br /> Public Health Services Environmental Health Division (EHD) in considering site closure <br /> certification <br /> 1.1 Background <br /> In 1986, the SJCMVCD removed three underground storage tanks (USTs) from the site and <br /> excavated soil beneath the gasoline UST to a depth of 31 feet below grade A soil and <br /> groundwater investigation conducted by Weiss Associates on behalf of the SJCMVCD in 1987 <br /> consisted of soil borings and the installation of three groundwater monitor wells (MW-1, MW-2 <br /> and MW-3) to a depth of approximately 50 feet (see Figure 2) While the investigation <br /> identified the presence of hydrocarbon compounds in soil beneath the location of the former <br /> gasoline etectable hydrocarbon compoun presence was found in the three <br /> groundwater monitor wells A low permeability soil layer at approximately 32 feet below the <br /> ground surface was believed to have acted as a barrier to downward migration of hydrocarbon <br /> compounds to groundwater The Weiss Associates study also concluded that, based on <br /> groundwater elevations in the three monitor wells, groundwater beneath the site flowed in a <br />' north-northeasterly direction <br /> In December 1991, ROY F WESTON, INC (WESTON®) began a quarterly groundwater <br />' monitoring program on behalf of the SJCMVCD WESTON's first sampling effort found that <br /> only one of the three monitor wells contained enough water to sample Consequently, the EHD <br /> requested that an additional monitor well be installed on the site northeast of the former tank <br /> area to evaluate the possible downgradient migration of hydrocarbons in groundwater The new <br /> well (MW-4) was installed in July 1992 according to the EHD-approved WESTON work plan <br /> A detailed description of the well installation and sampling activities was presented in the <br />' WESTON report entitled Well Installation and Quarterly Groundwater Monitoring Report, dated <br /> October 14, 1992 <br /> Analysis of the samples from the initial sampling of the new well (MW-4) on August 25, 1992 <br /> showed total petroleum hydrocarbons-gasoline fraction (TPH-G) and benzene, toluene, <br /> ethylbenzene and xylenes (BTEX) to be non-detectable Furthermore, all groundwater sampling <br />' events conducted after August 1992 (November 1992 and January 1993) have shown non- <br /> detectable results for TPH-G and BTEX in the new monitor well and any other wells containing <br /> sufficient water to sample <br />' Srh5RPT51S1CmVCU1 WP <br /> 1 08129!94 <br />