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w A S S O C I A T E S I N C 4, seven feet away, but helium was measured at 20% in well VW-5s, located 17 feet away several hours after the test was terminated During vapor the p extraction act on test, extraction flowrates ranging from 35 to 42 cfm resulted in vacuums of up to 0 6 inches of water in vadose well VW-5s located 17 feet from the extraction well Vacuums measured in wells VW-5d, VW-2d, and RW-1 were less than those measured during the first pilot test because the subsurface had not equilibrated following the sparge test ' Again, no response was observed in wells MW-1 and VW-4, located dust 6 to 7 feet from the extraction well, indicating that preferential pathways for airflow in the subsurface exist Influent VOC vapor concentrations monitored with a flame ionization detector were measured at 476 and ' 609 parts per million Laboratory results of the vapor samples indicated that volatile hydrocarbons were detected in the influent samples Approximately 0 16 pounds of TPHg was removed during the pilot test Laboratory results of the effluent vapor sample indicated a destruction efficiency of over 98 percent for all constituents analyzed 4.3.3 Conclusions The helium detected in well VW-5s, 17 feet from the sparge well but not in well VW-4, 7 feet from the sparge well indicated a preferential airflow pathway The unmeasurable flowrates were likely attributed to a combination of the silts and clays found in the subsurface and to the size of the compressor The radius of influence of vapor extraction during vapor extraction testing varied from less that 6 ' feet to approximately 17 feet Petroleum hydrocarbons were removed at an average rate of 19 pounds per day 4_4 Air Sparge Testing—June 30, 1999 4.4.1 Methods and Procedures On June 30, 1999, ATC performed a short-term air sparge test The purpose of the test was to determine if the lack of airflow during the previous pilot test was due to subsurface stratigraphy and/or equipment size, evaluate petroleum hydrocarbon removal rates from the saturated zone as a result of sparging, evaluate the propagation of air and helium injected below the groundwater ' surface, and collect infection flowrate and pressure data for the possible design of an air sparge system The pilot test involved air sparging only, no vapor extraction was involved Well MW-1 was used as the air injection point Prior to the test, a grab groundwater sample was collected from well MW-1, the infection point Two air compressors capable of producing flows up to 10 cfin were connected in series and used to pressurize the well casing to 10 psi Airflow was initiated at a flowrate of 2 cfm and gradually increased to 4 cfm Helium was then infected at a flowrate of 2 ' W 162574 011pilot-fs report doc 7