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Monitoring Well Installation Report 10 Quik Stop Market No 121 Page 3 the City of Manteca municipal well No 15, 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 Louis Avenue (in front of the Exxon station) to determine whether groundwater contamination was migrating from that corner toward the Quik Stop site Information obtained during the Cone Penetration Test (CPT) investigation conducted in June 2000, indicated the groundwater was impacted with petroleum hydrocarbons, mainly in the vicinity of Quik Stop Markets' 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 (CPT-3) 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 is associated with the Exxon site Subsurface geologic conditions in the vicinity of CPT-I (Figure 2) 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, a dense sand to gravelly sand was encountered This granular unit was followed by a 12-foot interval of sand, sandy silt and silty clay From 54 feet to 66 feet, a very stiff, clayey silt-to-clay was encountered, with some localized "hard pan" (calcium cemented sand and/or clay) material The "hard pan" material appears to be an impediment to vertical contaminant migration Below 66 feet and extending to the bottom of the bore hole, a 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 500 feet to the southeast of the site Subsurface conditions encountered at this location also consisted of alternating layers of clay, silty clay, sand and gravelly sand to a depth of approximately 43 feet Below this interval and extending to a depth of 62 feet, the soil became less granular and consisted of silty sand to silty clay and clay There were several localized areas of hard pan material CPT-2 was terminated at 62 feet due to refusal Groundwater in the vicinity of monitoring well MW-3 continues to contain the highest petroleum hydrocarbon concentrations at the subject site It appears some MTBE may have migrated to a lower portion of the aquifer, to a depth of 35 to 38 feet, as confirmed by the water sample collected at CPT-I In addition, the water sample collected from CPT-I was also reported to contain low concentrations of tetrachloroethene, a widely used dry cleaning solvent The source of the tetrachloroethene is not known No petroleum hydrocarbon concentrations were detected in the two water samples collected at CPT-2, which was located approximately 500 feet southeast of the site, in the direction of the City of Manteca municipal well No 15