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2.9 Bi-Weekly Eree-Eluting Hydrocarbon Measurement and Removal Since the discovery of the free-floating hydrocarbons in monitoring well MW-5, ASE has measured the thickness of the free-floating hydrocarbons I in monitoring wells MW-5 and MW-6 and then removed all accumulated free-floating hydrocarbons in the well with a bailer every two weeks prior to January 2000 and monthly after January 2000 2. 10 December 1999 Area Well Sury-ey In December 1999, ASE conducted a more detailed area well survey f o r the site than the one previously conducted This survey identified 57 wells within a 2,000-foot radius of the site Of these 57 wells, 39 are domestic, 3 are irrigation only, and 15 are of unknown usage The closest properties to the site with wells are directly to the east, directly to the southeast and across Airport Way to the west (at least 120-feet from the site) These wells are located in upgradient or crossgradient directions from the site (based on groundwater flow in the shallow zone) The ' closest wells potentially downgradient of the site are approximately 120- feet northwest the site One of these wells is a domestic well The closest well directly downgradient of the site's USTs is an irrigation well located approximately 240-feet north of the site The closest domestic well directly downgradient of the site's USTs is located approximately 300-feet Inorth of the site 2. 11 March 2000 Monitoring Welllustallatmn I In March 2000, ASE installed groundwater monitoring wells MW-11 through MW-15 and piezometers P-1 through P-5 Monitoring wells MW-13 through MW-15 and piezometers P-1 through P-5 are screened between 9 and 19-feet bgs Monitoring wells MW-11 and MW-12 are Iscreened between 55-feet bgs and 70-feet bgs Free-floating hydrocarbons were present in monitoring well MW-5, no free-floating hydrocarbons were present in any of the surrounding monitoring wells or piezometers High hydrocarbon concentrations were detected in groundwater samples collected from monitoring well MW-6, Iwith toluene, ethyl benzene and total xylene concentrations in this well exceeding DHS MCLs Groundwater samples collected from monitoring well MW-4 contained 3 S ppb benzene and 43 ppb MTBE Groundwater samples collected from monitoring well MW-3 contained 12 ppb MTBE and 44 ppb tert-butanol (TBA) Groundwater samples collected from downgradient monitoring wells MW-13 and MW-14 contained 490 p p b Frank's One Stop Interim Remediation System Workplan — September 2000 I -5-