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H SER�710ESPUBLIC HEALT <br /> SAN JOAQUIN COUNTS <br /> (OGI KHAN`A MD.,M-P.H <br /> HealthO(ficer <br /> P.O. Bax 2009 • (1601 East Hazelton Avenue) <br /> • Stockton, California 95201 <br /> (209) 468-3400 <br /> 1 i <br /> DAN KIRK �, � ,� � � <br /> SHELL OUL COMPANY . <br /> P O BOX 5278JUL 0 71992 <br /> CONCORD CA 94520-9998 -� J <br /> Re: Hammer Lane Shell SITE CODE: 1660 <br /> 7910 Lower Sacramento Road <br /> Stockton CA 95210 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) <br /> has reviewed and has comments on the following submittals prepared by Aegis <br /> Environmental: <br /> -Letter dated June 9, 1992, responding to the PHS/EHD letter dated <br /> April 17, 1992. <br /> -Quarterly Groundwater Monitoring Report dated June 10, 1992. <br /> -Letter dated June 15, 1992, requesting continued reduction in sampling <br /> frequency. <br /> PHS/EHD has continued to evaluate the potential threat that the residual soil <br /> contamination poses to groundwater quality. Residual contamination is associated with <br /> the northern dispenser and former underground storage tanks, #3 and #4. Residual soil <br /> contamination will require further investigation, remediation and possibly additional <br /> groundwater investigation prior to consideration of a closure request. <br /> Aegis used sampling points, SB1 and PI-9, to define the residual contamination associated <br /> with the northern dispenser. According the "Soil Sampling Location Map" prepared by <br /> Delta Environmental and dated September 25, 1989, PHS/EHD estimates the distance <br /> from the northern dispenser sample, T-3, to SB1 is 18 feet and to PI-9 is 12 feet. This <br /> differs from the estimate presented by Aegis. PHS/EHD agrees that gravel backfilled <br /> trenching does provide a conduit for migration of contamination. However, the distance <br /> and sampling depth of SBI and PI-9 do not provide adequate data to define documented <br /> contamination associated with the northern dispenser. <br /> The sampling frequency of monitoring wells, MW1 and MW3, may remain reduced to <br /> semi-annually providing the gradient remains to the northeast. Quarterly measurements <br /> of groundwater elevations of all monitoring wells should continue. Additionally, continue <br /> quarterly sampling of the downgradient monitoring well, MW2. <br /> A Division of San Joaquin(bounty Health tare Services <br />