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SOIL VAPOR EXTRACTION PILOT STUDY REPORT San Joaquin County Montgomery Ward Auto Service Center Public Health Services Departnient 5400 Pacific Avenue Stockton, CA Site Code 2I63 I 8.0 ASSESSMENT OF REMEDIAL PARAMETERS ' Data obtained during the pilot test field activities were used to assess remedial parameters as shown below I8.1 Results from Soil Vapor Extraction Tests The field data obtained from the soil vapor extraction tests were used to assess remedial parameters (see sections 8 1 1 through 8 1 3) 8 1 1 Radius of Influences (ROI)for Vapor Extraction IThe primary variable in designing a VES is the radius of influence (ROI) which is the area over which an induced vacuum is effective in mobilizing and extracting contaminants Each vapor extraction well generates a radius of influence that is a function of well vacuum and soil permeability For this study, the ROI of an extraction well will be estimated to be the distance from the well at which the observed subsurface vacuum is greater than 0 1 inch of water column (in WC) The steady state vacuum measurements at all probes (using VEW-1A as the extraction well) are shown as a function of the distance of the probes from VEW-1A in Figure 14 The two bars at each distance are measurements made at the same probe for two different vacuum extraction rates at VEW-1A Thus, the purple bars indicate measurements made at the probes when VEW-1A was being extracted with a vacuum rating of 81 in WC I Although the data generally follow the expected pattern of exponential decrease of vacuum with distance, there are four irregularities observed First, the extremely low vacuum values observed at a distance of 25 feet from VEW-1A (at SP-1A and SP-1B) are suspect EAI believes these values are incorrect due to possible problems in the probes for which the correct readings cannot be obtained at these probes Second, the vacuum observed at SP-3 is higher than that observed at SP-2 although SP-2 is closer (14 feet) than SP-3 (35 feet) to VEW-1A EAI believes this indicates anisotropic subsurface conditions with preferred vapor flow in the direction of SP-3 I The third irregularity is observed at a distance of 60 feet from VEW-1A (at probe SP-713) where a positive pressure reading was observed (since vacuum is represented by positive numbers, pressure is indicated by negative numbers) This could be due to either the fact that ISP-7 is set deeper than the well or that there may be problems with SP-7 similar to SP-1B Finally, at a distance of 112 feet from VEW-1A (at SP-5) consistent positive pressure readings were observed This observation may be real and could result from subsurface flow conditions that are set up as a result of the vapor extraction Vacuum measurements using VEW-113 as an extraction well are shown in Figure 15 Note that the observations regarding SP-lA, SP-IB, SP-3, SP-5 and SP-713 when using VEW-1A as extraction well, also applies to this scenario In addition, SP-6 also exhibits positive pressure and may be a result of subsurface flow conditions The trend in probes SP-713, SP-6 and SP-5 Isuggest that this is a natural phenomenon Project No 1232 - 10 - ENVIRONMENTAL AUDIT, INC