ARCHIVED REPORTS_XR0008538 - Laserfiche WebLink

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$PATER CLEAR G R O U P ErtVlraMm[RtRI Se Utcrs beneath the 8,000-gallon UST and the fuel island Based on this finding the County requested the that E-Z Serve Petroleum Marketing Company (E-Z Serve) complete a preliminary site assessment Per the County's request NEI, contracted by E-Z Serve, supervised the drilling and sampling of three soil borings in the tank backfill area in August 1991 The results of this investigation found that a 11 three soil boring locations contained measurable quantities of fuel hydrocarbon contamination In June and July 1995 five on-site monitoring wells (MW-1 through MW-5) were installed by TPE to depths of approximately 90 feet bgs In December 1993 three off-site morutoring wells (MW-6 through MW-8) were installed by HETI These wells were also completed to a depth of 90 feet bgs Results of these investigations indicated that moderate concentrations of hydrocarbons remained in the dissolved-phase in the area surrounding the former tank pit In 1994, E-Z Serve directed Brown and Caldwell to initiate remedial actions at the subject site In December 1994 Brown and Caldwell installed one air sparge/soil vapor extraction well (VW-1) and two vapor extraction wells (VW-2 and VW-3) for pilot testing purposes The results of the pilot testing work indicated that the subsurface was responsive to contaminant recovery when soil vapor extraction and air sparge methods were used concurrently Based on these results Brown and Caldwell recommended in their May 1995 Corrective Action Plan (CAP) that a SVE/AS system be installed to restore soil and groundwater quality to acceptable levels Groundwater rose over the course of the site assessment It has risen from almost 90 feet to approximately 50 feet below ground surface (bgs), significantly above the screened interval of the wells installed during the earlier stages of the investigation (MW-1 through MW-8) The vapor wells, however,now serve as monitoring wells, as static water stands within their screened interval with a sufficient water column to allow for representative groundwater samples to be collected Regional Geology and Hydrogeology The subject site lies within the San Joaquin Valley, a north-south trending structural trough which is part of the Great Valley Province The San Joaquin Valley is bounded by the Sierra Nevada Mountain Range to the east and the Coastal Ranges to the West The valley flow beneath the site consists of Quaternary-age alluvial sediments deposited by the San Joaquin river and its tributaries Page 2