ARCHIVED REPORTS_XR0006740 CASE 1

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3.0 CONCLUSIONS, RECOMMENDATIONS AND PROJECT S T STATUS I Since the wells were last monitored in December 2000, groundwater levels rose an average of 0 06 feet, the groundwater flow direction shifted approximately 30 degrees to the northwest, and the groundwater gradient decreased (i e , flattened) slightly Relatively consistent with previous results, concentrations of TPH-as-gasoline and BTEX compounds are restricted to MW-2 near the dispenser islands, and MTBE is concentrated in MW- 4 downgradient of the USTs The plume of MTBE in groundwater appears to extend to the north and east of the site toward domestic water wells located on Raylow Avenue The plume appears to be mostly delineated to the south (upgradient) by MW-1 and to the west (cross-gradient) by MW-3 The vertical extent of impacted groundwater is not defined Based on these conclusions, Ramage Environmental recommends that a work plan be prepared, outlining the following course of environmental corrective action 1 To attempt to define the extent of impacted groundwater, drill several additional CPT borings and collect additional discrete groundwater samples One of the additional CPT borings should be located near CPT-4 to investigate and discretely sample groundwater-bearing zones beneath 78 feet Other CPT borings should be located in the northern undeveloped part of the site and to the east of the site along Raylow Avenue 2 To confirm and monitor the concentrations of gasoline hydrocarbons detected in deeper groundwater-bearing strata, install a series of monitoring well clusters The deeper wells should also be considered for groundwater extraction and hydraulic control of the plume of impacted groundwater The cluster wells should be screened across discrete groundwater- bearing intervals of interest The upper groundwater-bearing zones should be cased to prevent leakage and cross-contamination The number of well clusters and the specific well construction should be based on the results of the additional CPT data j3 To further delineate the lateral extent of impacted groundwater at the groundwater table, install additional groundwater table monitoring wells in the northern undeveloped part of the site and to the east of the site along Raylow Avenue 4 Continue to monitor and sample groundwater from the existing monitoring wells and on-site domestic well on a quarterly basis The groundwater samples should be analyzed for TPH-as- gasoline, BTEX, MTBE, DIPE, ETBE, TAME, TBA, and 1,2-DCA by EPA Method 8260B The next monitoring and sampling event is scheduled for June 2001 5 Given the proximity of the on-site domestic well to the plume of impacted groundwater, this well should be abandoned and city water service should be connected to the site 7