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It would also be possible to estimate several other parameters from <br /> this information. The results of this analysis are presented <br /> I below. <br /> 3 . 0 SAMPLE COLLECTION <br /> 3. 1 Photo-ionization data <br /> I Hydrocarbon concentrations in recovered soil vapors have been <br /> reduced from a high approaching 2 , 500 ppm in mid-1991 to <br /> approximately 500 ppm at the end of 1992 to the current 200-300 <br /> ppm. A plot of the inlet hydrocarbon vapor concentrations versus <br /> time is presented in Figure 3 . Comparison of inlet and outlet <br /> concentrations indicates that the hydrocarbon destruction <br /> efficiency continues to be greater than 90 percent. <br /> 3.2 Collection of Air Samples <br /> I On February 22 , 1993 a representative of GeoAudi.t collected an air <br /> sample from a port located between the moisture drop-out drum and <br /> the supplemental fuel intake source. while the engine was running, <br /> the sample was collected in a vacuum container supplied by Coast to <br /> Coast Analytical Services. The sample was then transported to <br /> Coast to Coast for analysis . <br /> IOn April 28 , 1993 a second air sample was collected from the sample <br /> port between the moisture drop--out drum and the supplemental fuel <br /> intake source. The sample was collected using an air pump and two <br /> tedlar bags supplied by Calscience Environmental Laboratories, Inc. <br /> Because the air pump was unable to pull against the vacuum of the <br /> vapor extraction system, the sample was collected while the engine <br /> was stopped. The engine was shut off, a valve between the sample <br /> port and the supplemental fuel intake was closed (to avoid the <br /> possibility of contamination from this source) and the sample was <br /> immediately collected. It was transmitted to Calscience for <br /> analysis. The chain of custody and laboratory report are attached. <br /> 4 . 0 FINDINGS <br /> 4 . 1 Relationship Between PID Measurements and Actual <br /> Hydrocarbon (TPH as gasoline) Concentration <br /> IThe results of the laboratory analysis of the air samples and the <br /> PID values collected at the same time are presented in Table 4 . <br /> I PID readings exceeded laboratory measurements by better than a <br /> factor of 2 during both monitoring events. Actual concentrations <br />• were roughly 43e of PID measurements. Current PID values are <br /> ranging from 200 ppm to 300 ppm; assuming that the actual <br /> concentrations being removed remain at 43% of the PID values, <br /> actual hydrocarbon concentrations are ranging from 80 ppm to 130 <br /> 2 <br />