ARCHIVED REPORTS_XR0007643 - Laserfiche WebLink

Home Browse Search

C A M B R I A sample from this well using a sampling pump that was set within the screened interval (107 to 115 fbg) The idea of this sampling event was to pump fresh groundwater from the formation to determine if there was groundwater impact at depth The results of this sampling event, performed on January 30, 2003, indicate that no TPHg, BTEX, MTBE, or other fuel oxygenates (including ethanol and methanol) were detected in this well If the MTBE detected in CPT-1 at 1 i 1 to 114 fbg were truly present, it would seem reasonable that MTBE would have been detected in the groundwater sample collected from well RW Because no MTBE was detected to the RW groundwater sample, this questions the validity of the MTBE detections in groundwater from boring CPT-1 Cambria evaluated the groundwater elevation data from well RW and compared them to the groundwater elevation data for the adjacent shallow screened well (MW-IA) to deterrmne if there is an upward or downward vertical groundwater gradient beneath this site (Table 4) The findings of this evaluation are that there is an upward vertical groundwater gradient beneath the site The existence of an upward groundwater gradient beneath this site precludes any downward rrugration of shallow groundwater that may be impacted Based on the discussion above, the anomalies noted with the TPHd and MTBE groundwater sampling data from CPT-1 along with the non-detect RW groundwater analytical results, and the upward vertical groundwater gradient, all suggest that the gasoline constituents have not migrated downward beneath the site RECOMMENDATIONS The periodic groundwater extraction program at the site was initiated in February 2000 in wells MW-IA and MW-2A Tank backfill well BF-1 was added to the program in March 2000 Initial MTBE concentrations in these wells were as high as 148,000 ppb As of the April 28, 2003 sampling event, MTBE concentrations in wells MW-IA, MW-2A, and BF-1 are 100 ppb, <5 0 ppb, and 140 ppb, respectively The periodic groundwater extraction program at this site appears to have been effective in reducing MTBE concentrations in groundwater beneath the site Historical groundwater sampling data for this site indicates that MTBE is generally the only gasoline constituent detected in groundwater beneath this site Based on the current low concentrations of MTBE in groundwater beneath the site along with the fact that MTBE is no longer used as an oxygenate in Shell gasoline, it appears that the installation of the monitoring wells previously proposed is no longer warranted Cambria recommends no further monitoring . wells be installed at this site and that the existing monitoring wells continue to be monitored quarterly 0813 6