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3 0 CONCLUSIONS, RECOMMENDATIONS AND PROJECT STATUS <br /> ' Since the wells were last monitored in March 2001, groundwater levels dropped an average of <br /> 1 20 feet, the groundwater flow direction shifted approximately 45 degrees to the northeast, and <br /> the groundwater gradient increased Over the past four quarters, the groundwater flow direction <br /> has shifted between northwest and northeast, over a range of approximately 45 degrees <br /> Relatively consistent with previous results, concentrations of TPH-as-gasoline and BTEX <br /> compounds are restricted to MW-2 near the dispenser islands, and MTBE is concentrated in MW- <br /> ' 2 and MW-4 downgradient of the USTs Over the past four quarters, the concentrations of <br /> gasoline hydrocarbons in groundwater have generally declined, possibly due to previous source <br /> removal efforts The plume of MTBE in groundwater appears to extend to the north and east of <br /> the site toward domestic water wells located on Raylow Avenue The plume appears to be mostly <br /> delineated to the south (upgradient) by MW-1 and to the west (cross-gradient) by MW-3 The <br /> ' vertical extent of impacted groundwater is not defined Based on these conclusions, Ramage <br /> Environmental recommends that a work plan be prepared, outlining the following course of <br /> environmental corrective action <br /> 1 To attempt to define the extent of impacted groundwater, drill several additional CPT borings <br /> and collect additional discrete groundwater samples One of the additional CPT borings <br /> should be located near CPT-4 to investigate and discretely sample groundwater-bearing <br /> zones beneath 78 feet Other CPT borings should be located in the northern undeveloped <br /> ' part of the site and to the east of the site along Raylow Avenue <br /> 2 To confirm and monitor the concentrations of gasoline hydrocarbons detected in deeper <br /> ' groundwater-bearing strata, install a series of monitoring well clusters The deeper wells <br /> should also be considered for groundwater extraction and hydraulic control of the plume of <br /> impacted groundwater The cluster wells should be screened across discrete groundwater- <br /> bearing intervals of interest The upper groundwater-bearing zones should be cased to <br /> prevent leakage and cross-contamination The number of well clusters and the specific well <br /> construction should be based on the results of the additional CPT data <br /> ' 3 To further delineate the lateral extent of impacted groundwater at the groundwater table, <br /> install additional groundwater table monitoring wells in the northern undeveloped part of the <br /> site and to the east of the site along Raylow Avenue <br /> 4 Continue to monitor and sample groundwater from the existing monitoring wells and on-site <br /> domestic well on a quarterly basis The groundwater samples should be analyzed for TPH-as- <br /> ' gasoline, BTEX, MTBE, DIPE, ETBE, TAME, TBA, and 1,2-DCA by EPA Method 8260B The <br /> next monitoring and sampling event is scheduled for September 2001 <br /> 5 Given the proximity of the on-site domestic well to the plume of impacted groundwater, this <br /> ' well should be abandoned and city water service should be connected to the site <br /> 7 <br />