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! .t ^� X_ A S S O C l A 7 E S I N C During the vapor extraction test, extraction flowrates ranging from 3 5 to 42 cfin 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 lust 6 to 7 feet from the ' extraction well Laboratory results of the vapor samples indicated that volatile hydrocarbons were detected in the influent samples Approximately 0 16 pounds of TPHg were removed during the pilot test Laboratory results of the effluent vapor sample indicated a destruction efficiency of ' over 98 percent for all constituents analyzed t 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 Well MW-1 was used as the air injection point Prior to the test, a grab ' groundwater sample was collected from well MW-1 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 cfrn Helium was then ' injected at a flowrate of 2 cfin in addition to the air for a total flowrate of 6 cfin After 80 minutes of operation, helium was detected in well VW-5d but no helium was detected in well VW-4, seven feet away It was determined that the injected air and helium were channeling through the subsurface to well VW-5d At the direction of PHS/EHD, the air sparge test was terminated to prevent the migration of the plume to the north Results and field readings from the short-term air sparge test performed on June 30, 1999 are included in Appendix B ' Laboratory results of the groundwater samples collected from MW-1 before and after the test indicated that petroleum hydrocarbons increased during the test An injection rate of 4 cfm was attainable using two small air compressors Positive pressure was observed approximately 20 feet away from the injection point, with the highest measurements in well VW-5d Helium was also detected in this well at 18% ' 4.0 SUMMARY OF SOIL AND GROUNDWATER CONDITIONS ' 4_1 Extent of Hydrocarbon-Impacted Sail ' The lateral extent of gasoline hydrocarbons in soil is delineated by borings B-6 and B-7 to the west, boring B-5 to the south, boring Bpi to the east, and boring B-15 to the north The highest concentrations of residual gasoline hydrocarbons appear to be north and west of tank T3, from ' approximately 15 feet bsg to the top of the groundwater surface at the tune of the investigation(42 feet bsg) TPHg was detected in soil samples at concentrations ranging from nondetect to 5,100 parts per million The extent of TPHg In soil is shown on Figure 5 4_2 Extent of Hydrocarbon-Impacted Groundwater Based on the analytical results from groundwater samples collected from wells MW-1 through MW-5, RW-1, VW4, VW-5s and VW-5d on July 6, 1999, and from wells PZ-1, VW-1, VW-2d ' W 162574 011CAP mpost doe 5