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' 29 August 2001 S AGE-NC Project No 96-0229 ' Page 4 of 5 ' deeper ground water conditions Deeper ground water in the area of MW-1 (48 to 53 feet bsg)is Impacted by TPH-g,BTEX, MTBE, deeper ground water in the area of downgradient well MW-IOB is impacted by MTBE ' • The dissolved TPH-g, BTEX and MTBE plume is at least 25 feet thick in the area of MW-1 (screened 48 to 53 feet bsg) and MW-2 (screened 25 to 45 feet bsg) ' • MTBE was detected in the sample collected from well MW-1 (screened 48 to 53 feet bsg) In deeper ground water, but was not detected in the samples collected 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 possibly DIPE-Impact may be present crossgradient to downgradient of the site at deeper depths (Figure 5) ' • The greatest concentrations of off-site dissolved MTBE were detected in downgradient wells MW-6 at 910,ug/l, MW-7 at 630 ggll and MW-8 at 25 tgll and MW-10A at 34,ug/l • Increasing TPH-g, BTEX and MTBE were reported in water samples collected from wells ' MW-3 and MW-1 OA, increasing TPH-g was reported from MW-7 and increasing MTBE was reported from MW-6 and MW-10B, suggesting the plume has shifted towards the northeast 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) Based on maps depicting the estimated extent of dissolved TPH-g (Figure 4), the horizontal extent of the dissolved hydrocarbon plume has not been defined north of MW-7 or northwest of MW-2, the vertical extent of hydrocarbon-impacted ground water has not been delineated in any direction 5.0. RECOMMENDATIONS Based upon data collected during June 2001, AGE recommends ' • Preparation of a feasibility study work plan to assess remedial alternatives for feasibility and .to aA_CSS +I,- d l—d petroleum. i,..,a...,..,,-t,o 1,,.,,e at+I,n �o VVJL LV a41\il\+JJ LllV 1JjV1YV peLl VlV lull lir LLr cu VVIl p1L11116+ "t Llll.. al LV • Preparation of a corrective action plan (CAP), the CAP should include results of any feasibility studies to determine appropriate remediation alternatives for the site • 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 Advanced GeoEnvironmental,Inc