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44) 22 March 2001 AGE-NC Project No 96-0229 Page 4 of 5 bsg) • The decrease of ground water elevation of approximately 2 feet between the April 2000 and August 2000 monitoring events is probably attributable to seasonal fluctuation • The dissolved TPH-g,BTEX and MTBE plume is at least 28 feet thick in the area of MW-1 (screened 48 to 53 feet bsg) and MW-2 (screened 25 to 45 feet bsg) • MTBE and DIPE-impact was only detected in the sample collected from well MW-1 (screened 48 to 53 feet bsg) in deeper ground water, but were not detected from shallow water on-site wells MW-2 (located 5 feet from MW-1), MW-3 or MW-4 Implying that an undelineated MTBE and DIPE-Impact may be present crossgradient to downgradient of the site at deeper depths • The greatest concentrations of off-site dissolved MTBE were detected in downgradient wells MW-6 at 26,ug/l, MW-7 at 59 gg/l and MW-8 at 64 ,ug/l Based on data collected from the intervening well MW-6, the MTBE-impact detected in wells MW-7 and MW-8 may not be related to the Pacific Car Wash release • The elevated concentrations of petroleum hydrocarbons detected in samples collected from wells MW-1, MW-2, MW-3 and MW-6 Indicate that these wells are within or near the dissolved petroleum hydrocarbon"core area'of the plume (Figure 4) • The vertical extent of MTBE-impacted ground water has not been delineated in the area of MW-1 or downgradient in the area of MW-6, MW-7 and MW-8 5.0. RECOMMENDATIONS Based upon data collected during December 2000, AGE recommends • Preparation of a work plan for cone penetrometer testing (CPT) soil borings and/or the installation of deeper ground water monitoring wells located adjacent MW-1 and downgradient in the area of MW-6 to further assess the vertical extent of the plume • Preparation of a feasibility study work plan to assess remedial alternatives for feasibility and cost to remediate the dissolved petroleum hydrocarbon plume at the site • Preparation of a corrective action plan (CAP), the CAP should include results of any 1h ' hetCfeds1D1ydLdeteie aJPP0f -Le eiieUlati011 alicT� iaiivis lir t 51 • Performance of a receptor survey to locate potential receptors within 2,000 feet of the site, results of the receptor survey should be included in the CAP • Continued utilization of wells MW-1 through MW-10 for quarterly ground water monitoring and sampling, the next monitoring event is tentatively scheduled for 27 March 2001 Advanced GeoEnvironmental,Inc