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' 04 March 2002 AGE-NC Project No 95-0130 ' Page 5 of 6 ' VW-2A and VW-2B suggesting a significant TBA-impact to ground water at the site • The elevated concentrations of petroleum hydrocarbons detected in samples collected from wells MW-6 (A, B and C), MW-7B, VW-1 (B and C), VW-2 (A and B) and VW-3 (A and B) indicate that these wells are within or near the dissolved petroleum hydrocarbon "core area" of the plume (Figures 4 and 5) • The lateral extent of the dissolved petroleum hydrocarbon plume is not known toward the northwest, north, northeast, east and southeast of the area bound by wells MW-1 through VW-3, the vertical extent is not known in any area (Figures 4 and 5) I ' S.O. RECOMMENDATIONS Based upon the results of the fourth quarter 2001 investigation, AGE recommends ' • Continued quarterly ground water monitoring, the next quarterly ground water monitoring event Is tentatively scheduled for March 2002 �. • Conduct future quarterly ground water monitoring events concurrently with the Knowles Rock site (102 South Wilson Way) and the Arco AM/PM site (130 South Wilson Way), AGE recommends that a well-head elevation survey be performed by a state-certified surveying engineer so that reported ground water elevations are relative to a City of Stockton benchmark datum ' • Continued utilization of wells VW-IB, VW-1C, VW-2A,VW-2B, VW-3A and VW-3B for characterization of ground water conditions in the "core area" • Preparation of a feasibility study work plan for a ground water pump testing to obtain general aquifer charactenstics such as hydraulic conductivity, transmissivity, storativity and drawdown at various pumping rates Results of the pump test would be utilized to estimate ' a radius of influence for the zone of capture of dissolved petroleum hydrocarbons • Preparation of a feasibility study work plan for an 8-hour soil vapor extraction feasibility pilot test • Preparation of an interim remediation work plan to continuously operate a ground water extraction system in the area of VW-1, VW-2 and VW-3 to Inhibit further oft-site migration ' of the fuel impacted-ground water plume • Installation of additional shallow-screened ground water monitoring wells on-site as wells MW-1, MW-2, MW-3, MW-4 and MW-5 have become significantly"drowned" • Installation of additional multi-level ground water monitoring wells off-site towards the east and northeast to assess down-gradient impact to shallow and deeper ground water Advanced GeaEnvironmental,Inc