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I s ?n t ' 29 March 2001 AGE-NC Project No 98-0448 ' Page 4 of 5 conditions ' Comparing the August 2000 monitoring event to the January 2001 monitoring event, decreases in concentrations of dissolved petroleum hydrocarbons were quantified in ground ' water samples collected from wells MW-4A and MW-4B (Table 2) However, based on the overall increased petroleum hydrocarbon concentrations quantified from well MW-4B (screened 45 to 50 feet bsg) during the June 1999, September 1999, April 2000 and August ' 2000 monitoring events, AGE suspects that well EW-1 (screened between 15 and 45 feet bsg)may be a vertical conduit between shallow depth ground water(approximately 15 to 30 feet bsg) and deeper depth ground water(approximately 45 to 50 feet bsg) , I • Ground water elevation at the site decreased an average 1 14 feet between the August 2000 ground water monitoring event and the January 2001 ground water monitoring event ' • A_trend of increasing ground water elevation was observed at the site between October 1994 and June 1998 Since June 1998, ground water elevation has varied between 7 and 10 feet below mean sea level • Previous laboratory results of ground water samples collected from wells MW-1, MW-4B, MW-6 and MW-8 indicates a minor dissolved WE impact • The elevated petroleum hydrocarbon concentrations previously detected in water samples collected from wells MW-1 and MW-2 (screened between 20 and 40 feet bsg), MW-4A I (screened between 8 and 33 feet bsg) feet and MW-4B (screened between 45 and 50 feet bsg) suggest that these wells may be screened within or near the dissolved petroleum hydrocarbon "core area"of the plume • The dissolved petroleum hydrocarbon plume appears to be sufficiently contained within the current array of ground water monitoring wells I 5.0. RECOMMENDATIONS Based upon the results of this investigation, AGE recommends _ p g • Continued quarterly ground water monitoring The next quarterly monitoring and sampling event is tentatively scheduled for 23 April 2001 4 • Implement soil vapor extraction and in-situ air sparging at the site as per Remedial Action Work Plan (RAP), dated 07 July 2000 and approved by the PHS-EHD by letter dated 14 July 2000 AGE anticipates initiation of the remediation system by April 2000 • A work plan to abandon ground water extraction well EW-1 was submitted to the PHS-EHD Advanced GeoEnvironmental,Inc f