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1 <br /> 3 <br /> First Quarter 2002 Monitoring,Sampling,and Air Sparge Test Report <br /> 7-Eleven, Inc,Store#19976, 1399 North Main Street, Manteca, CA May 10,2002 <br /> ' Air Sparge Test <br /> ' Test well SPA is a double-nested sparge well Installed to a total depth of 50 feet below grade, perforated <br /> from 30 to 35 feet and 45 to 50 feet below grade <br /> ' On February 6, 2002, an air sparge test was conducted using well MW-2 for vapor extraction purposes, <br /> and the sparge well for air infection The wells are located 5 feet apart Initially, the soil vapor extraction <br /> ' (SVE) unit (a 150-cubic feet per minute [cfm] King Buck trailer unit)was allowed to warm up on propane <br /> and then set to extract from well MW-2 at between 50 to 65 Inches of water applied vacuum Extracted <br /> vapor levels without air sparging ranged up to 1,000 parts per million by volume (ppm[v]) After <br /> ' conducting SVE for two hours to establish steady-state conditions, air was Infected Into the deeper section <br /> of well SPA using an oil-less air compressor After Initiating air Infection, extracted vapor levels in well <br /> MW-2 were measured for increases expected as a result of the sparging process Air sparging volatilizes <br /> hydrocarbons/oxygenates from saturated-zone soils and groundwater and transfers them to the vadose <br /> zone for capture by SVE After Initiation of sparging, extracted vapor levels in MW-2 increased gradually <br /> over time to 1,600 ppm(v) at about 30 minutes after sparge initiation Dissolved oxygen In well MW-2 <br /> ' increased from baseline levels of 0 72 milligrams per liter(mg/L) to levels of 7 to 8 mg/L after 30 minutes <br /> of sparging <br /> MThese data Indicate the area of sparging influence In SPA includes the region of MW-2, and therefore <br /> treatment using well SP-1 should be successful at reducing dissolved hydrocarbons/oxygenates In well <br /> ' MW-2 and the surrounding area <br /> Also, on February 6, SVE was conducted for a period of two hours using the horizontal vent wells <br /> ' (installed in the former tank pit backfill) Extracted vapor levels ranged up to 4,000 ppm(v) (Attachment 3) <br /> Conclusions and Recommendations <br /> Interim remediation activities appear to have reduced dissolved hydrocarbon/oxygenate levels in well <br /> MW-2 It is recommended that remediation In the area of MAMA continue (using the horizontal vent <br /> wells installed in the tank pit)to reduce dissolved concentrations In this part of the site Air sparging is <br /> recommended to be added to SVE Remediation is recommended to occur on a two-week schedule for at <br /> ' least six months, after which site status and path to closure will be discussed with the San Joaquin County <br /> Public Health Services Department as applicable <br /> • <br /> I <br /> ' 19975021 COC <br />