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4.0 CONCLUSIONS AND RECOMMENDATIONS Groundwater levels have dropped an average of 1 40 feet since groundwater levels were last measured on August 26, 1999 The groundwater gradient was calculated at 0 002 foottfoot in a southerly direction This represents a shift in groundwater flow from the historical northeast direction I Concentrations of dissolved gasoline hydrocarbons bans in the groundwater samples collected this quarter from MW-6, MW-7, VW-1 and VW-2 remain relatively consistent with previous sampling results Groundwater in VW-2 continued to contain concentrations of TPH-as-gasoline, BTEX and MTBE Additionally, analytical testing by EPA Method 8260, indicated the presence of TBA and 1,2-DCA to groundwater collected from VW-2 The SVE system and air sparge pump operated consistently during the quarter Mass removal rates have declined to 8 03 pound per day Between September 15 and December 2, 1999, a total of 1,542 4 pounds of hydrocarbons were removed by the system Since startup on June 2, 1999, a total of 7,066 5 pounds have been removed Based on these conclusions, Ramage Environmental recommends the following course of environmental corrective action 1 Continue to monitor and sample groundwater from the four water table wells on a quarterly basis Given the shift in the groundwater flow to the south, the irrigation well located approximately 50 feet south of the former USTs should also be sampled The next quarterly groundwater monitoring is scheduled for February 2000 2 ENSR to continue operating and monitoring the soil vapor extraction system and air sparge pump 3 Drill a soil boring near the former UST to confirm the remediation of vadose zone soil and to evaluate the vertical extent of impacted soil and groundwater To reduce cross-contamination of lower groundwater-bearing zones, the boring should be advanced with a cone penetrometer test rig and groundwater-grab samples should be collected with a SimulProbeo 7