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3.0 CONCLUSIONS AND RECOMMENDATIONS r� Since May 1992, the groundwater surface has risen almost 22 feet This extreme rise in the groundwater table has resulted in a groundwater elevation significantly above the screened interval of the five groundwater monitoring wells This situation has probably resulted in inconsistent groundwater flow direction and gradient interpretations and groundwater sample collection and analytical results that are unrepresentative of groundwater table conditions To obtain data representative of groundwater table conditions, groundwater samples were only collected for analysis from two deep soil vapor extraction wells with screen intervals coinciding with the current groundwater table Groundwater samples collected this quarter from soil vapor extraction wells VW-1 and VW-2 indicate a general decrease in gasoline hydrocarbon concentration since the last sampling was performed on November 14, 1997 In VW-1, the concentration of TPH-as-gasoline declined from 5,700 ppb on November 14, 1997 to 1,300 ppb this quarter Benzene concentrations also declined in VW-2 from 370 ppb to 120 ppb In VW-1, concentrations of TPH-as-gasoline and benzene were also lower this quarter than on November 14, 1997 To comply with recent Regional Water Quality Control Board guidelines, the gasoline oxygenate compound MTBE was analyzed Groundwater sampled from VW-2 contained 650 ppb of MTBE Based on the results of the groundwater monitoring and sampling activities, Ramage Environmental recommends the following environmental corrective actions 1 To take advantage of the existing vapor extraction well network and prior vapor extraction pilot testing work already completed at the site, initiate active remediation by soil vapor extraction To substantiate this remedial action, a Corrective Action Plan (CAP) and design of the selected remedial alternative should be prepared for regulatory review 2 The approved final CAP and design should be used as a bid document to obtain at feast three bids for the construction and operation of the selected remedial alternative so that pre-approval can be secured by the UST Cleanup Fund 3 To further delineate the extent of impactedre-establish groundwater and re estab sh groundwater monitoring capability at the site, two additional monitoring wells should be installed Once installed, these wells and the two existing deep soil vapor extraction wells should be monitored and sampled on a quarterly basis for at least one year 4