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Quik Stop No 121 Closure Report i CCI Project No 12118 Page 2 were analyzed using EPA Test Method 8260 The laboratory reported all three wells to have detectable concentrations of MTBE Monitoring well MW-3 was reported to contain the highest MTBE Ievel, at a concentration of 49,000 ug/L Monitoring wells MW-2 and MW-I were reported to have detectable concentrations of MTBE, at 3 ug/L and 11,000 ug/L, respectively Based on the January and February 2000 sample results, the Central Valley Regional Water Quality Control Board (RWQCB) and the San Joaquin County, Public Health Services, Environmental Health Department (County) requested a Work Plan to further define the vertical and lateral extent of the petroleum hydrocarbon plume at the Quik Stop site CCI had knowledge that the City of Manteca's municipal well No 15 was located approximately one-quarter mile southeast of the subject site, near the corner of Franciscan Way and Agate Street, therefore, CCI proposed to collect soil and groundwater data between the Quik Stop Market site and the municipal well to determine whether impacted groundwater was migrating toward the well In addition, CCI proposed to collect a grab water sample on the north side of West Louise Avenue (in front of the Exxon station) to determine whether groundwater contamination was migrating from that corner toward the Quik Stop site Due to the high levels of MTBE in well MW-3, CCI contracted Industrial Waste Utilization (IWU) of San Jose, California on March 30, 2000 to pump groundwater from well MW-3 IWU pumped a total of 1,300 gallons from the well In June 2000, CCI conducted an Additional On-Site and Offsite Soil and Groundwater Investigation The information obtained during that investigation indicated the groundwater was impacted with petroleum hydrocarbons, mainly in the vicinity of Quik Stop Market's fuel tanks, on the southeast side of the site, near monitoring well MW-3 Low concentrations of TPHg were detected in the shallow water sample collected on the north side of West Louis Avenue, in front of the Exxon gas station Since this location is up-gradient of the Quik Stop site, it is possible the TPHg detected at CPT-3 was associated with the Exxon site. CCI collected sounding data from CPT-1, located in the vicinity of monitoring well MW-3 The subsurface geologic conditions in the vicinity of MW-3 were found to be composed of alternating layers of silty sand and sand, with some silty clay and clay from the surface to approximately 32 feet The material was found to be dense, with localized areas of very dense material From 32 feet to 42 feet below the ground surface (bgs), dense sand to gravelly sand was encountered This granular unit was followed by a 12-foot interval of sand, sandy silt to silty clay From 54 feet to 66 feet bgs, a very stiff, clayey silt-to-clay was encountered, with some localized "hard pan" (calcium cemented sand and/or clay) material Below 66 feet and extending to the bottom of the bore hole, very dense sand to gravelly sand was encountered to a total depth of 79 5 feet It appears the subsurface geologic conditions encountered at the Quik Stop site are consistent with off-site regional data CCI collected off-site CPT sounding data from CPT-2, located approximately