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The assessment of hydrocarbon impacted soil indicated that vadose zone contamination was restricted to the area immediately below the former UST location. GeoAudit installed a vapor well near the center of the contaminant plume for remediation and a vapor extraction system (VES) was installed in August 1991. The VES was operated under permit requirements of the San Joaquin Air Pollution Control District order number 91-61. 23 Remediation Remediation began in 1991, and progress has been summarized in periodic reports, the most recent submitted in January 1994. Between August of 1991 and July of 1993, the VES was in operation for approximately 90 percent of the time with total operational hours exceeding 13,500. 3.0 GROUNDWATER DEPTH AND GRADIENT According to the San Joaquin County Flood Control District map, the depth to water in the fall of 1990 was approximately 65 feet with a regional southwest gradient. However, locally the gradient varies widely from northeast to southwest. In August of 1988, GTI reported a flow direction of north-northeast with a gradient of less than 1 percent. 4.0 PROPOSED ASSESSMENT The San Joaquin County Public Health Services - Environmental Health Division (PHS/EHD) is requiring the installation of monitoring wells to investigate if groundwater is still impacted at the site. In a letter dated August 30, 1993, the PHS/EHD recommended that "confirmation soil sampling occur at the same time as replacement of monitoring wells." GeoAudit recommends the installation of three (3)groundwater monitoring wells.The wells should be installed in the general locations of MW-1, MW-2 and MW-3. Additionally, soil samples from the replacement of MW-2(located in the sidewalk along Sierra Nevada Street) will be utilized for confirming the success of the VES remediation. The locations of the monitoring wells are depicted in Figure 3. If needed, an additional soil boring may be drilled near MW-2 and VW-1, to evaluate the removal of hydrocarbons from the soil plume. 5.0 PROCEDURES To meet the project objectives, the following procedures will be performed: 1) Prepare a Site Health and Safety Plan in accordance with the Occupational Safety and Health Guidance Manual for Hazardous Waste Site Activities - Prepared by National Institute for Occupational Safety and Health, Occupational Safety and 0-b�.I A.&5—k—I.e. 2 Cows B.Irq%?X9V 1.1 i