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t <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> m Donna K.Heron,R.E.H.S. Carl Bor man,R.E.H.S. <br /> Q, 304 East Weber Avenue, Third Floor g <br /> Director Mike Huggins,R.E.H.S.,R.D.I. <br /> , <br /> At OlsenR.E.H.S. Stockton, California 95202-2708 <br /> - - Douglas W.Wilson,R.E.H.S. <br /> Program Manager Telephone: (209) 468-3420 Margaret Lagorio, R.E.H.S. <br /> 6 I j <br /> Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-0138 Robert McClelloq R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> KAREN PETRYNA SEP ] 6 2002 <br /> SHELL OIL PRODUCTS USA <br /> PO BOX 7869 CAFILE COPY <br /> BURBANK CA 91510-7869 <br /> RE: Shell Service Station #204-7524-4 Site Code:1883 <br /> 3011 W. Ben Holt Dr. RO#: 0000486 <br /> Stockton, CA., 95207 <br /> San Joaquin County Environmental Health Department (EHD) has reviewed <br /> Cambria's "Work Plan Approval" dated August 28, 2002 and has the following <br /> comments. <br /> Due to Cambria's great reluctance to installation of a repeatable sampling point at <br /> 119 feet below ground surface (' bgs) and preference for a phased approach to the <br /> vertical assessment of impacted groundwater, EHD has reevaluated the data <br /> submitted to date for the site and will concur with Cambria's preferred approach, <br /> but may require confirmational sampling of groundwater at SB-13-119 at a later <br /> date to resolve the issue. EHD notes that it is the responsibility of the consultant to <br /> select the appropriate sampling techniques to suit site conditions and to supervise <br /> the sampling to ensure that valid data is acquired. To date, Cambria has <br /> speculated that cross-contamination has occurred, but has offered no observations <br /> or data to support the argument. EHD accepts the data in question as being valid <br /> until demonstrated otherwise. <br /> As a result of EHD's reexamination of the available data, two currently /_ <br /> unaddressed concerns were identified. 0 <br /> 1. The plume of MtBE impacted groundwater appears to be unstable and <br /> actively migrating since September 2001 as evidenced by increasing <br /> concentrations in samples from MW-1 and MW-5. The northern and <br /> northeastern margins of the dissolved MtBE plume are not delineated. <br /> 2. Four laterally continuous, significant sand intervals underlie the site, with the <br /> shallowest being the only one monitored at present, with the third to be <br /> assessed through MW-1-82 and MW-2-82. The second sand interval, <br /> extending roughly from 40' to 50' bgs is not currently monitored and has only <br /> been 'grab-sampled' in the top of the interval possibly two times. In view of <br /> the unstable state of impacted groundwater in the monitored zone, the <br /> second sand interval should be immediately assessed and permanent <br /> monitoring wells installed where most advantageous to collect repeatable <br /> groundwater samples. <br />