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spa Chevron a Chevron Chevron Products Company March 2, 1997 6001 Bollinger Canyon Road Budding L San Ramon CA 94583 P 0 Box 6004 San Ramon CA 94583-0904 Mr Harlin Knoll Marketing—Sales West San Joaquin County Public Health Services Phone 510 842 9500 P O Box 388 Stockton, CA 95201-0388 Re Former Chevron Slafion 4 9-8632 575 Grantline Rd Tragy, CA Attached Groundwater Monitoring Report(Blaine Tech, 1/30/97) Dear Mr Knoll Please find attached a report dated January 30, 1997 which was prepared by Chevron's consultant, Blaine Tech Services (Blaine Tech), to descnbe the results of groundwater monitoring that was performed at the$ subject site on January 7, 1997 In January Blaine Tech gauged and sampled all five site-related wells, including the sump pump on the property to the north Samples from each monitoring well were analyzed for the presence of TPHGas, TPHDiesel, BTEX constituents, and MTBE Samples from well MW-1 were also analyzed for HVOC's, SVOC's, soluble metals, and total oil and grease The samples collected from the sump pump were analyzed for TPHGas, BTEX constituents, MTBE, HVOC's, and total recoverable petroleum hydrocarbons The measured direction of groundwater flow was again, toward the northwest There were reported detections of dissolved petroleum hydrocarbons at each monitoring well and at the sump well The reported concentrations were similar to those detected during previous monitoring events Unidentified hydrocarbons within the diesel range of analysis were reported at all monitoring wells MTBF,was detected at wells MW-1 through MW-3 only There was no MTBE detected at well MW-4 or the sump well There were no detectable concentrations of HVOC's SVOC's or total oil and grease at well MW-1 There were unusually high concentrations (160 ppb) of Zinc detected in groundwater at well MW-1 All other metals were non-detect There were no HVOC's present at the sump well The measured hvdrocarbon concentrations at this well were consistent with regards to its location within the estimated contaminant plume boundary ' In evaluating groundwater data from the subject site, several consistent trends have been recognized For example, the direction of groundwater flow has always been toward the northwest With one exception, there have been no detections of HVOC's, SVOC's or total oil and grease at well MW-1 Except for what are thought to be background levels of Zinc, no soluble metals have been detected at well MW-1 MTBE has consistently been detected at wells MW-1 through MW-3 but, not at well MW-4, and unidentified hydrocarbons within the diesel range are present at all four wells Considering these trends, Chevron proposes the following modifications to the current monitoring and reporting program - Gauge and sample wells MW-1 through MW-4 and the sump well quarterly -Analyze samples from MW-1 through MW` 4 for TPHG, TPHD, BTEX, and MTBE Analyze samples from the sump well for TRPH, BTEX, and MTBE