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early in the quarter, resulted in significant volatilization of hydrocarbons that previously had not been <br /> recovered by the extraction unit However, it is uncertain whether the hydrocarbons were volatilized <br /> ' from groundwater or soil, because no groundwater samples had been collected from the deep well in <br /> prior quarters <br /> ' Comparison of the laboratory result (Appendix B) of the sample collected on January 2 with the PID <br /> reading on that date yields unsatisfactory correspondence When converted from parts per million by <br /> volume (ppmv) to parts per million by weight, the laboratory result of 1,033 ppm is more than 50% <br /> ' greater than the value of the PID reading of 620 ppm Similarly, the laboratory result of 20 ppm for the <br /> exhaust sample is 500% higher than the 4 ppm measured by the PID The daily PID readings may <br /> therefore be incorrect on the low side during the quarter If so, it implies that air sparging had an even <br /> greater effect than is indicated by the PID data <br /> 4.2 Weight of VOC's Destroyed <br /> ' Th6 weight of VOC's extracted during the quarter can be computed by using the average PID <br /> g g p <br /> concentration from Figure 5 and the cumulative volume of extracted vapors from Figure 4 <br /> tWEIGHT OF VOUS =CF x VAPOR x 10-6 x 100 moVwt <br /> ' 379 cf/mole <br /> =4 608 x 10� ft' x 970 x le x 100 moVwt <br /> 379 cf/mole <br /> =4 470 x 10 SIbs <br />' 379x102 <br /> = 1179 lbs <br /> 5.0 GROUNDWATER MONITORING <br />' 5.1 Monitoring Procedures <br /> r <br />' Groundwater monitoring took place on February 20, 1996 The depth to groundwater was measured <br /> in all six monitoring wells and in the Aep vapor extraction well Depth measurements were recorded <br /> on the Well Monitor Report (Appendix C) Per prior agreement with San Joaquin County PHS/EHD, <br />' monitoring well MW-5 was purged of approximately 3 well volumes (3 gallons) before sampling, but <br /> none of the other wells were purged or sampled except the deep vapor extraction well Due to the <br /> minimal amount of water in that well and its slow recharge rate, however, VE-I was sampled without --- <br />'- purging The water purged from MW-5 was stored in a 55-gallon drum near the vapor extraction unit <br /> for later disposal <br /> 1 4 , <br />