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Site History Boyett Petroleum(419 S.Main St.,Manteca) ' Page 6 of 11 conducted on foot and residents were contacted by knocking on residential (houses, duplexes/triplexes, and apartments) doors and inquiring of the owner/renter. The actual and potential locations of wells were identified either by a caretaker or by a neighbor living within the SRS area. Three well locations were identified within the study area. No DWR well records were available for two of the three wells. During the 2002 sensitive receptor survey for the site vicinity, a well was thought to be located at 188 W. Oak Street. When asked, the owner indicated there was no well. During the SRS reconnaissance, the resident at 123 W. Stockton Street indicated that a well at this Oak Street location was used by its owner. A well was located at 144 W. Wetmore Street during the 2003 SRS reconnaissance. Condor requested permission from the property owner to sample the well at this location. Based on conversations with the resident at 123 W. Stockton Street, there may be several improperly abandoned wells within the residential area. These wells are potential vertical conduits for hydrocarbon contaminants in groundwater in the vicinity of ' the site. On July 15, 2003, a Condor representative was onsite to collect water level measurements and redevelop monitoring wells MW-1 through MW-3 and MW-6 through MW-9. Attempts were made to redevelop monitoring well MW-9 by surging and pumping the groundwater in the well with a surge block and pump. This redevelopment procedure was ineffective due to large volumes of medium-grained, well- rounded, and well-sorted sand infiltrating the well. The infiltration of sand resulted in a decrease of 0.10 ' feet in the measured total depth of MW-9. The water purged from MW-9 was light brown in color and cleared during redevelopment. Heavy amounts of sand periodically interfered with the pump equipment. Based on the results of the redevelopment procedure applied to MW-9, the previous loss of MW-4 and ' MW-5 to sand infiltration, and the historic high sediment content observed in all the site monitoring wells, the decision was made not to surge or pump the remaining monitoring wells. In addition, it was determined even if redevelopment was successful, the potential benefits would be limited as water level ' • measurements collected from the site monitoring wells indicated the wells contained only two to three feet of water. A provisional increase in the groundwater monitoring frequency was instituted in July 2003 in which water levels in monitoring wells MW-1 through MW-3 and MW-6 through MW-9 will be measured on a monthly basis and groundwater samples will be collected for MTBE laboratory analysis for a period of six consecutive months. On July 22, 2003, a Condor representative was on site to measure water levels in ' and collect groundwater samples from the specified monitoring wells. Laboratory analytical results for the groundwater samples collected at the site on July 22, 2003, indicated that MTBE was detected in the groundwater samples collected from MW-1, MW-2, MW-7, and MW-9. Static water level measurements ' collected on July 22, 2003, generally indicated a groundwater flow direction to the southwest, consistent with that reported in the Second Quarter Monitoring Report June 2003, dated July 30, 2003. In addition, the average groundwater elevation (14.32 feet) decreased with respect to the previous quarterly monitoring event by 1.06 feet. On August 6, 2003, Condor collected a water sample from the well located at 144 West Wetmore Street, ' Manteca, California. Laboratory analytical results of the groundwater sample indicated that TPH-G, BTEX, and gasoline oxygenates/additives were not detected at or above the laboratory reported detection limits. ' On August 19, 2003, a Condor representative was on site to measure water levels and collect groundwater samples at monitoring wells MW-1 through MW-9. Groundwater samples were not collected from MW4 and MW-5 because they were dry. Laboratory analytical results for the groundwater samples collected at the site on August 19, 2003, indicated that MTBE was detected in the groundwater samples collected . from MW-1, MW-2, MW-7, and MW-9. Static water level measurements generally indicated a