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3.0 CONCLUSIONS AND RECOMMENDATIONS The results of the groundwater sample analyses indicate that the lateral extent of impacted groundwater is undefined to the north (upgradient), west and south (downgradient) of the former UST excavation However, the lateral extent is defined to the northeast of the former USTs by MW-1 Vertically, the possible impact to deeper ' groundwater-bearing zones has not been investigated Based on these results, Ramage Environmental recommends the following course of environmental corrective action 1 To further delineate the nature and extent of metallic debris and/or buried drums within the former UST excavation, conduct a geophysical survey of the area The survey should include the use of a magnetic gradiometer (MAG), electromagnetic ' terrain conductivity meter (EM), and ground penetrating radar (GPR) The MAG and EM should be operated over a five foot grid The GPR should locally be used over anomalous EM or MAG areas to further define any localized subsurface variations ' 2 Define the lateral extent of impacted groundwater by expanding the groundwater monitoring well network This should include the installation, development, surveying and sampling of at least three additional wells Possible locations for the new wells are the sidewalk or Charter Way center lane south (downgradient) of the site, the motel courtyard north (upgradeint) of the former UST excavation, and within the Sierra Nevada Street right-of-way west of the site 3 Monitor and sample groundwater from all monitoring wells on a quarterly basis for at least four consecutive quarters The groundwater samples should be analyzed for TPH-as-gasoline, BTEX and oxygenates by EPA Method 8260B 4 Conduct a survey of water wells within a 2,000-foot radius of the site The survey should include a review of well completion reports at the Department of Water Resources offices in Sacramento, a review of city and county records, and a reconnaissance walk of the site vicinity to verify well locations and operating status 5 Evaluate the risk posed by residual petroleum hydrocarbons on human health and the environment The risk assessment should be based on analytical data collected to date, the results of four quarters of groundwater monitoring and sampling, and the findings of the water well survey 6 Based on the findings of the risk assessment, request regulatory closure or proceed with the evaluation of possible remedial alternatives 7