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Vapor Extraction Test Report Former Thrifty Oil Service Station # 172 September 14, 1995 For the purpose of determining the range of hydrocarbons present in the subsurface, soil vapor samples were collected from the test wells (Monitoring Wells VW-A, VW-B, VW-C), during the beginning and end of their respective tests The samples were analyzed for: 0 Total petroleum hydrocarbons as gasoline (TPH-G) using EPA Method 8015 modified for gasoline; and • Benzene, toluene, ethylbenzene, and total xylenes (BTEX) using EPA Method 8020 Refer to Appendix C for copies of the official Laboratory Reports and Cham of Custody Records. 3.0 CAARACTERIZATTON ANALYSIS Stabilized vacuum responses in the observation wells were assumed to represent steady-state conditions, and were used to calculate the soil transmissibility to air ('kh/µ), the soil permeability (k), and an effective radius-of-influence (ERI). In order to estimate these parameters, a steady-state solution of Darcy's law, as applied to compressible gas flow, was used to simulate the subsurface flow conditions. Refer to Appendix D for a mathematical description of the Darcy analytical solution, and for the calculations performed to estimate the soil transmissibility to air, soil permeability, and ERI. ERI was also estimated graphically by plotting the log of distance from the test well versus observed vacuum response. ERI is estimated to be the distance from the extraction well where the vacuum response is equal to 0.1 inches of water, and can be read directly from the graph (Figure 2). 4.0 FINDINGS AND DISCUSSION 4 1 FIELD OBSERVATIONS The amount of vacuum that could be applied to each test well by the internal combustion (IC) engine test equipment was limited by the minimum oxygen requirement of the IC engine and the low oxygen content of the extracted soil vapor. Field observations recorded during the tests were as follows: • During the constant-flow-rate test from Test Well VW-A, a vacuum level of 7.5 in. H,,O was measured in the extraction well while extracting vapors at a flow rate of approximately 16.6 scfm. Vacuum responses ranging from 0.05 to 0.31 in. H2O were detected in Observation Wells VW-B, VW-C, MW-1, MW-3, MW-4, and My-8. These observation wells are located at distances ranging from 26 to 90 feet from the test well. - 2