ARCHIVED REPORTS XR0011192 - Laserfiche WebLink

Home Browse Search

4.0 DATA ANALYSIS 4.1 Graphical Summary Monthly summaries of daily air flow rates and other parameters for the quarter are included in Appendix A In order to graphically illustrate the operation of the system, data for air flow rate since January 1996 and total cubic feet of extracted vapor since September 1995 are plotted in Figures 3 and 4 PID readings and all 1996 laboratory results are graphed in Figure S to illustrate the effect of the system on soil vapor concentrations More so than in any previous quarter, flow rates on operating days were very constant, generally ranging from 40 to 45 cfm The only exception was the last few days of the year, when the unit was -being gradually shut down in anti cpation of the December 31 expiration of the operating permit After the installation of VE-2,there was a marked increase in vapor concentrations in the deep-well inlet stream Concentrations rose from 40 ppm to more than 2,000 ppm An increase was to be expected, since VE-I "deep" was submerged below the static water level most of the year and was therefore drawing little vapor, but such a large rise was surprising It indicates that the radius of influence of VE-1 "deep" has been Iess than anticipated, and that an unexpectedly large volume of gasoline remains within the vadose zone below the clay layer that separates the shallow and deep wells This will probably be corroborated by soil analytical data from the new extraction well when the data are released by Emcon • Laboratory analysis of the vapor samples P p collected in December indicates that the gasoline concentration withm the range of influence of VE-I "shallow" has not decreased since the last sample was collected in August In fact, when converted from parts-per-million by volume to parts- per-million by weight,the concentration has risen slightly from 137 pprn to 192 ppm (Figure 5) The sample collected from VE-2 had a TPH-g concentration of 673 ppm by weight This result can not be compared directly with the concentration of 2,885 ppm that was detected in the sample from VE-1 "deep" in February, but the result is encouraging It is also considerably below the concentrations detected by the PID at the inlet port, suggesting that the PID readings are inflated by the passage of the vapors through the water drop-out drum before being measured at the inlet 4.2 Weight of VOC's Destroyed The weight of VOC's extracted during the quarter can be computed from the mean vapor concentration in the shallow well and the cumulative volume of extracted vapors Visual examination of Figure 5 suggests that a concentration of 1,500 ppm is a reasonable estimate of the - mean vapor concentration during the quarter as measured by the PID (the laboratory concentration may have been somewhat lower) • 4