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23 March 2001 AGE-NC Project No 97-0301 ' Page 10 of 11 • The core of the dissolved petroleum hydrocarbon plume appears to be located in the area of ' MW-1 and MW-7, the ground water is impacted by TPH-g,TPH-d, TPH-k, BTEX and 1,2- DCA, low concentrations of MTBE were also detected at MW-1 ' • The elevated petroleum hydrocarbon concentrations detected in water samples collected from well MW-7 (screened between 20 and 40 feet bsg) suggest that this well is screened within or near the dissolved petroleum hydrocarbon"source area'of the plume (Figure 13) ' • AGE suspects that TPH-g and BTEX detected at in samples collected from wells MW-2 and MW-3 were due to sampling MW-7 first which may have caused cross-contamination despite equipment decontamination • Low concentrations of 1,2-DCA were detected in water samples collected from MW-5, moderate concentrations were detected to MW-1 samples and substantial 1,2-DCA ' concentrations were detected in MW-7 The dissolved 1,2-DCA plume appears to be at least 60 feet thick in the area of MW-1 and MW-5 ' • Laboratory results of ground water samples collected from MW-5 (screened 80 to 90 feet bsg) suggest that the dissolved petroleum hydrocarbon plume extends at least 90 feet bsg 7.0. RECOMMENDATIONS Based upon data collected during December 2000, AGE recommends ' Continued quarterly ground water monitoring The next quarterly monitoring and sampling event is tentatively scheduled for March 2001 • Continued utilization of wells MW-1, MW-2, MW-3 and MW-4 for characterization of ' ground water conditions at the site Ground water monitoring wells MW-5, MW-6 and MW-7 were installed at the site in December 2000 and should be included in the quarterly 1 ground water monitoring program • Review of historic records which should include records on file with the local fire department, building department or planning division and cross-referenced telephone directories to identify potential petroleum-hydrocarbon sources on or near the property, • Review of EDR Sanborn Fire Insurance Maps(if available) and aerial photographs to assess the possibility of usage, storage and disposal of petroleum hydrocarbons at the site or on surrounding properties, • Additional vertical assessment of soil and ground water is warranted at the site AGE proposes to drill cone penetrometer testing (CPT) soil bonngs to characterize the vertical extent of hydrocarbon-impacted ground water at the site prior to installation of additional Advanced GeoEnvironmental,Inc i I I ,I