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'f L A May 24, 1996 Quarterly Monitoring Report Chapin Brothers Automobile Repair Facility Stockton, California 2.3 Groundwater Sampling yky f L Following purging, each monitoring well was allowed to recover to greater than 90% of the original well volume. Each monitoring well was sampled using a 1.5-in diameter disposable polyethylene bailer lowered approximately half-way through the groundwater surface in the well. Groundwater samples were then transferred into two sterile 40-m1 glass vials equipped with Teflon septa. Each via]was checked to,,ensure that no air bubbles were entrapped, and then each sample container was labeled, logged on a chain-of-custody form, and placed into an ice chest kept at 4°C using ice. The samples were transferred the following day into the custody of Sparger Technology Environmental Laboratories. No free product was found in the wells. Water purged from the wells was sealed in 55- gallon drums and temporarily stored onsite. 3.0 GROUNDWATER SAMPLE ANALYSIS Groundwater samples were analyzed for TPHg using EPA Method $015 (modified) and purgeable aromatic hydrocarbons (BTEX) using EPA Method 8020. All analyses were conducted by Sparger Technology Analytical Laboratories of Sacramento, California, which is certified by the State of California for the requested analyses. Results of analytical testing indicate that gasoline is present in the two onsite wells nearest the former tanks, MW I and MW4, at concentrations of 23 and 70,parts per million(ppm) respectively. The volatile constituents BTEX were also detected in those wells at relatively high proportions. Except for xylenes at 0.0009 ppm, no gasoline or petroleum constituents were detected in MW2 located north of the site. Gasoline was detected in MW3 and MW5, located on properties west of the site, at concentrations of 1.7 and 2.9 respectively. All of the volatile constituents were also detected in these wells. Analytical results for each constituent tested are listed in Table 2. Analytical reports and completed chain-of-custody forms are presented in Appendix A. .p 4.0 GROUNDWATER GRADIENT The groundwater gradient beneath the site was calculated from surveyed wellhead elevations and groundwater surface elevation measurements collected from the monitoring wells. Well casing elevations were measured to the nearest 0.01 ft by Underwood and Rosenblum of San Jose, California, a licensed surveyo''. These data were used to calculate the elevation of the R 530-001 - 4 - LUSH GEOSCIENCES