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tSOIL VAPOR EXTRACTION PILOT STUDY REPORT San Joaquin County Montgomery Ward Auto Service Center Public Health Services Department 5400 Pacific Avenue Stockton,CA Site Code 2163 ' Vacuum measurements using both VEW-1A and VEW-113 as extraction wells are shown in Figure 16 Note that the observations regarding SP-1A, SP-113, SP-7B and SP-5 when using ' VEW-1A as extraction well, also applies to this scenario In order to be able to calculate reasonable values for ROI, the various suspect data (SP-lA, ' SP-IB, SP-5, SP-6 and SP-713) were omitted The remaining data (SP-2, SP-3, SP-4, and SP-8) were plotted on a scaled plot Figure 17, 18 and 19 show these scaled plots using three different extraction well configuration (VEW-1A, VEW-113, and VEW-lA and VEW-113 combined ) The data points in these figures were fitted with a trend line using a fourth order ' polynomial The ROI was then calculated as the X-intercept of the location where this trend line crossed the value of 0 1 in WC on the Y-axis ' The ROI calculated for each scenario is as follows Well Vacuum ROI ' VEW-lA 81 in WC 60 feet VEW-1A 140 in WC > 100 feet VEW-113 115 in WC 60 feet VEW-1A and VEW-1B 140 in WC > 100 feet 8 1 2 Measurement of Soil Permeability A primary consideration in the application of vapor extraction for contaminant removal is vapor flow, and vapor flow is a function of soil permeability Highly permeable soils (such as sands and silty sands) will be more amenable to vapor extraction techniques than less ' permeable soils (such as clays and silts) Soil vapor permeability is analogous to aquifer permeability and can be determined in a similar fashion by measuring the vacuum differential at varying locations created by withdrawal of vapors from a single vapor extraction well Vacuum measurements made at intervals of 30 minutes, at all the probes, were used to determine the soil permeability By plotting these data on a log scale, a straight line can be I fitted to the part of the graph where the vacuum values are changing as a function of time The slope of this line is related to the soil permeability as shown below Slope = Q/[4*Pi*m*(k/M)] Iwhere I Slope Slope of the line depicting vacuum versus time in a semi-log plot Air flow rate from the extraction well in = Stratum thickness (I a the screened interval) M — Viscosity of air (1 8 X 10-4 glcm-s) k _ Soil air permeability PI 3 141592654 This equation can be rewritten as k = [Q*M]/[4*Pi*m*Slope] I IProject No 1232 - 11 - ENVIRONMENTAL AUDIT, INC