ARCHIVED REPORTS_XR0009258 - Laserfiche WebLink

Home Browse Search

QUARTERLY GROUNDWATER MONnIDF ING REPORT 4445 Pershing Avenue Stockton California I In December 1991, Aegis installed, developed, and sampled one groundwater monitoring well, MW-4, in response to the San Joaquin County Public Health Services Environmental Health Department's letter dated October 7, 1991, requesting, "repeatable sampling from I a monitoring well downgradient from the probable source " The results of the monitoring well installation were reported to Shell in a "Hydrogeologic Assessment Results and Quarterly Groundwater Monitoring Report," dated April 27, 1992 ESince January 1992, Emcon has been retained by Shell to collect quarterly depth-to-groundwater measurements and groundwater samples from the four wells on f site The data, including the laboratory analytical reports, are provided to Aegis for 1 quarterly reporting (Appendices A and B) 4.0 GROUNDWATER MONITORING 4 1 Groundwater Measurements On April 21, 1992, Emcon personnel collected measurements of the depths-to-groundwater in wells MW-1, MW-2, MW-3, and MW-4 Since January 21, 1991, groundwater levels have risen in the four wells (Figure 3) The increase ranged from 0 58 to 0 64-feet (Table 1) On the basis of the April 21, 1992, measurements, groundwater is estimated to flow to the northeast (Figure 4) at a gradient of approximately 0 004 ft/ft Previous groundwater levels are summarized in Table 1 All groundwater elevation measurements were made from the referenced wellhead elevations, measured to the nearest 0 01 foot, and conducted according to the Emcon sampling procedures (SP) referenced in Appendix A 4 2 Water Sampling and Analysis On April 21, 1992, Emcon personnel collected groundwater samples from wells MW-1, MW-2, MW-3, and MW-4 The samples were delivered under chain-of-custody to NET Pacific of Santa Rosa, California, a state-certified analytical laboratory, for chemical analysis Sample collection was conducted according to the Emcon SP referenced in Appendix A The samples were analyzed for concentrations of a) total petroleum hydrocarbons, as gasoline, by GC/FID Method 5030, b) benzene, toluene, ethylbenzene, and total xylenes by EPA Method 8020, and c) ethylene dibromide by EPA Method 504 The analysis indicated benzene concentrations in all four wells were below laboratory detection limits On May 12, 1992, Emcon personnel collected a groundwater sample from well MW-2 The sample was delivered under chain-of-custody to Sequoia Analytical of Sacramento, California, a state-certified analytical laboratory Sample collection was conducted according to the Emcon SP referenced in Appendix A The sample was analyzed for concentrations of fecal coliform The analytical results are summarized in Table 2 The analytical reports and chain-of-custody forms are included in Appendix B IConcentrations of benzene reported for April 21, 1992, are shown on Figure 5 89 015B QMR 2