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i I ' 26 October 2000 . AGE-NC Project No 96-0229 ' Page 4 of 5 ' • The decrease of ground water elevation of approximately 3 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 27 feet thick in the area of MW-1 and MW-2, the dissolved BTEX and MTBE concentrations appear to increase with increasing depth over the sample interval ' • TBA was detected in water samples collected from wells MW-4, MW-7 and MW-8 during the April 2000 monitoring event Due to abnormally high laboratory reporting limits at MW-1,MW-4,MW-6,MW-7 and MW-8,TBA may also be present at concentrations below the laboratory determined detection limits • The highest on-site MTBE concentrations have been encountered in ground water samples collected from the deeply drowned well MW-1 (screened 48 to 53 feet bsg), implying that an undelineated MTBE-impact maybe 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 a concentration of 21 ug/l, MW-7 at a concentration of 0 78 and MW-8 at a I• concentration of 32 µgll 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 I • 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 I5.0. RECOMMENDATIONS IBased upon data collected during August 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 • Preparatioti of a Corrective Action Plan (CAP), the CAP should include results of any • feasibility studies to determine appropriate remediation alternatives for the site A receptor survey should also be performed to locate potential receptors within 2,000 feet of the site, IAdvanced GeoEnvironmental,inc