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EXECUTIVE SUMMARY This PAR and CAP was prepared for regulatory review and approval The preparation of the PAR included the installation of 2 additional groundwater monitoring wells (MW-6 and MW-7) at the site so that the downgradient extent of impacted groundwater could be defined and so that a groundwater table monitoring capability could be re-established On May 1, 1998, groundwater was monitored and sampled from the 2 newly-installed wells and the 2 deep vapor extraction wells (VW-1 D and VW-21D), and the elevations of all on-site wellheads were surveyed to an established benchmark Depth-to-groundwater beneath the site ranged between 38 and 40 feet bgs and the groundwater table has risen an average of 6 18 feet since the wells were last monitored in February 1998 The groundwater flow direction remains northeast at a gradient of 0 0014 foot/foot Results of the groundwater sampling and analysis indicate that significant concentrations of gasoline hydrocarbons continue to exist in proximity to the former USTs The downgradeint extent of impacted groundwater is defined by MW-6 and MW-7 According to the existing soil analytical data, the majority of hydrocarbon mass is contained in vadose zone soil between 10 and 30 feet bgs Based on the vapor extraction testing conducted in May 1995, extraction flow rates in this interval ranged from 7 to 17 actual cubic feet per minute (acfm) at vacuums ranging from 40 to 82 inches of H2O These relatively high wellhead vacuums at low test flow rates are reflective of the relatively low permeability associated with the silt- and clay-based sediments of the vadose zone Vacuum responses of 0 2 inches of H2O occurred within an average distance of 28 feet from the extraction well Using a conservatively selected radius of influence (ROI) of 20 feet, the 4 existing vapor extraction wells (VW-1, VW-2, { VW-3 and VW-4) are constructed and positioned to effectively remediate the impacted sod A thermal oxidizer would provide the most economical initial processing and atmospheric discharge of treated extracted soil gas At a flow rate of 10 scfm per well, the anticipated TPH- 1 as-Gasoline mass extraction rate would be 216 ppd fob the full system Based on the findings of this PAR and CAP, Ramage Environmental recommends the following course of environmental corrective action 1 Upon regulatory approval of this PAR/CAP document, prepare a set of engineering plans for the design of the soil vapor extraction system, obtain the required air quality permits and submit the appropriate utility service applications The cost for these tasks has already been pre-approved by the UST Cleanup Fund 2 Solicit 3 bids to construct and operate the system The bids should be submitted to the UST Cleanup Fund for review and cost pre-approval 3 Upon UST Cleanup Fund pre-approval, construct, start-up, operate and maintain the system as specified in the design plans and bid specifications, and in accordance with the permits to construct and operate the system i 4 Continue quarterly groundwater monitoring and sampling The cost of 3 additional quarters has already been pre-approved by the UST Cleanup Fund 2