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f A Mr. Marty Hartzell Page 5 of 10 water were recorded in the observation wells during the test. The influent vapor sample contained 1,900 ug/1 TPHg. The IC Engine was also operated on VW2 for 8'.hours on December 13, 2001 and 8 hours on December 18, 2001. Flow rates fluctuated over a wide range during these to days, from 10-50 cfm on December 13 and from 15-80 cfin on December 18. The flow rate-on December 18 was never steady at 80 cfm, rather it bounced rapidly between 20-80 cfm during the first two hours of the test before stabilizing at between 15 and 35 cfm. Applied vacuums ranged from 20-45 inches of water on December 13 and 22-52 inches of water on December 18. Applied vacuums ranging from 0.3 to 0.8 inches of water were measured in observation well VW l a and applied vacuums of 0.5 to 1.1 inches of water were measured in well VWIb. Hydrocarbon vapor concentrations with the PID ranged from 385 to 651 ppm. The TPHg concentration in influent vapor samples collected on December 13 and December 18 was 2,100 ugll for both samples. Table 2 lists the physical data measured during the VET. Analytical data are summarized in Table 3. Laboratory data sheets and chain of custody documentation are included in Attachment D. EVALUATION OF TEST RESULTS Estimated Radius of Influence The effective radius of influence (ROI) for soil vapor extraction has been defined as the radial distance from a vapor extraction well at which recorded vacuum levels suggest that subsurface air flow occurs and is presumed to be sufficient for remediation. Most R01 concepts assume that subsurface air flows through homogeneous and isotropic soils and that short circuiting effects are negligible. Conventionally, the ROI is calculated for horizontal flow. However, flow should occur in three dimensions despite the attenuating effects of anisotropic sedimentary bedding. Methods for estimating an effective ROI vary due to the complexity of modeling the vapor extraction process. It is widely thought that an induced vacuum of 0.50 inches of water should be sufficient to induce subsurface airflow within the zone of influence for sandy soil types. Therefore, to determine the ROI one can plot the observed induced vacuum response as a function of the distance from the extraction well on a semi-log graph. A straight line is fit to the plotted data. The radial distance corresponding to the value of the cut-off vacuum (0.5 inches of water) is interpolated to be the effective ROI for a given extraction well at a certain applied vacuum. Air-flow modeling studies conducted by others suggest that the distance from the extraction well at which 1 percent of the applied wellhead vacuum persists should be sufficient to induce subsurface airflow and can be interpreted as an effective ROI (Chevron Research and Technology Company, Environmental Group, October 10, 1991). This method is based upon theoretical model predictions, which project that roughly 90 percent of the total air extracted from the well flows through soils within the radius of influence when a I% cut-off is used. The effective ROI is then G:XDmaIGRO[1NUZEgo ittlReporu5VETRPT doe