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r 4 0 CONCLUSIONS AND RECOMMENDATIONS ! This phase of environmental corrective action included drilling and soil sampling from five on-site soil borings and installing, developing, surveying and sampling three groundwater monitoring ' wells Soils encountered beneath the site consist of a fining-upward sequence of fine-grained siltciclastic sediments The depth to static groundwater beneath the site ranges from 39 31 to 40 34 feet bgs Groundwater flow is to the south-southeast at a relatively high gradient of 0 05 ' foot/foot Metal debris was detected in the vicinity of the former UST excavation This debris may be drums1 of waste soil and/or water not accounted for from earlier site investigation activities or other material used to backfill the former UST excavation Soil and groundwater beneath the site have been impacted by significant concentrations of gasoline hydrocarbons Concentrations of benzene, ethylbenzene and xylenes in groundwater exceed Title 22 Maximum Contaminant Levels for these compounds However, none of the five oxygenate compounds were detected in any of the soil or groundwater samples analyzed during the investigation Laterally, the extent of impacted soil appears to be limited to the footprint of the former UST excavation Vertically, the extent of impacted soil beneath the former UST excavation is defined�r /UG at a depth of approximately 55 feet bgs, on the basis of soil samples collected for analysis from the previously drilled soil boring B-1 y 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 the results of the results of this investigation, 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 . 12