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r 1 Mr. Marty Hartzell Page 3 of 10 groundwater samples previously collected from borings SBI and SB4 support the conclusion that these two laterally continuous fine-grained units have prevented downward vertical migration of contaminant to the shallow water table. The soil and analytical data collected from borings VW1 and VW2 were used to refine the estimate of contaminant mass remaining in the subsurface. Based upon all the data collected at the site, we have estimated that less than 300 kg, or approximately 650 pounds of gasoline remains in place beneath the former UST. Contaminant mass calculations are included in Attachment C. It is estimated that approximately 325 cubic yards of soil have been impacted by gasoline hydrocarbons beneath the site. The estimated extent of gasoline hydrocarbons in soil beneath the site is shown on Figure 3. VAPOR EXTRACTION TEST METHODOLOGY Vapor extraction testing consisted of a one-day VET followed by four days of operation, utilizing each well in tum. Del-Tech Geotechnical performed the one-day VET on December 11, 2001. The VET equipment consisted of an internal combustion (IC) engine equipped with dual catalytic converters, instrumentation for measuring air flow, air pressure/vacuum, temperature, and volatile organic compound concentrations. Vapor test wells VW1a, VWIb, and VW2 were each tested during the one-day VET. The IC engine was operated for approximately 2 hours in turn. Measurements of vapor flow rate in cubic feet per minute (cfm), applied vacuum in inches of water column and temperature were measured in each tested well every half-hour. The induced vacuum in the observation wells was also measured. Measurements of soil vapor hydrocarbon concentrations were taken with a photo-ionization detector (PID) every half-hour. One influent soil vapor sample was collected for laboratory analysis from each well after 2 hours of testing. The IC,engine was also operated on December 13'h for 8 hours (VW2), December le for 7.5 hours (VWIb), December 17'h for 9 hours (VWla), and December 18'h for 8 hours (VW2). Hours of operation were limited to between 8:00 a.m and 6:00 p.m. due to the close proximity of residences on three sides of the IC Engine. One influent soil vapor sample was collected each day for laboratory analysis. The vapor samples were delivered under chain of custody to State-certified Air Toxics Laboratories for analysis of TPHg and BTEX by EPA Method TO-3. Field notes are included in Attachment D. VAPOR EXTRACTION TEST RESULTS Vapor Test Well VW1a This well is screened from 23 — 26 feet in a silt/clay unit that corresponded to a hot spot during the initial field investigation. During the 2-hour vapor extraction test using well VWIa as the extraction well, the flow rate was 10 cfm at a vacuum of 40 inches of water during the first 30 minutes of the test. The flow rates fluctuated from 20 to 50 cfm at applied vacuums fluctuating from 40 to 60 inches a:�llNarGROUN�7itiganal oUicpmthVE71tFF'.dve