ARCHIVED REPORTS_XR0006746 CASE 1

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i 1 4.0 CONCLUSIONS AND RECOMMENDATIONS Based on the results of samples collected during this investigation, the horizontal and vertical extent of MTBE in soil and groundwater is not defined in the northeast part of the site, downgradient of the former and existing USTs Up-gradient and cross-gradient of the USTs the extent of impacted soil and groundwater is mostly delineated ' proximity Despite the of domestic wells to the plume of impacted groundwater beneath the site, p p ty and the shallow depth of these domestic wells, none of the water supply wells on the site and ' within 500 feet of the site appear to be impacted by gasoline constituent compounds Given that concentrations of MTBE were detected in all three groundwater-bearing zones investigated in the northeast (downgradient) part of the site, the plume of impacted groundwater is a threat to the nearby domestic wells ' 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 3 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 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 82608 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 15 1