ARCHIVED REPORTS_XR0008371 - Laserfiche WebLink

Home Browse Search

4 . 4 Groundwater Contamination ' Benzene was detected in MW-2 , MW--3 and MW-4 at concentrations of 16 ppb, 0 . 4 ppb and 4 . 1 ppb, respectively. TPH as gasoline and toluene were detected only in the sample from MW-2 at 210 ppb and 16 ppb, ' respectively. No ethylbenzene or xylenes were detected in any of the water samples . The results are tabulated in Table 3 . Several HVOC target analytes were detected in each monitoring well . ' The highest concentrations were 1, 1-Dichloroethylene at 5 . 6 ppb (MW-2) and 4 . 1 ppb (MW-4) , 1, 1-Dichlorethane at 5. 4 ppb (MW-3) and 1, 2-Dichloroethane at 1. 9 ppb (MW-3) . Table 4 summarizes the ' results of the HVOC analysis. The laboratory report and chain-of- custody are .included in Appendix C. ' Six HVOC target analytes were detected in the sample from the domestic well : 1, 1-Dichloroethene (42 ppb) ; 1, 1-Dichloroethane (47 ppb) ; Chloroform (1. 2 ppb) ; 1, 2-Dichloroethane (1. 6 ppb) ; Trichloroethene (6. 2 ppb) ; c-1, 2-Dichlorethene (7. 4 ppb) . I 5. 0 CONCLUSIONS AND RECOMMENDATIONS 5. 1 Soil Contamination Contamination was detected in only one soil sample from the vadose zone in this phase of investigation. Halocarbons were detected in MW-4 at 45 feet, but no petroleum hydrocarbons or volatile aromatic compounds were present. Monitoring wells MW-3 and MW-4 are located within 20 feet of the former UST cavity; therefore, it appears that the TPH and BTE&X contamination detected in soil samples from MW-1 is limited to a radius of approximately 15 feet from the former UST I location. In that area, field screening of soil samples from MW-1 indicated that soil contamination probably extends to a depth of between 75 and 80 feet (Applied Geosystems report dated December 22 , 1988) . Based on lithologic information obtained from the monitoring wells, we anticipate that the radius of influence of a vapor extraction or in-situ bioremediation well would be 25-35 feet. Therefore, a single vadose-zone well should be sufficient to remediate any residual soil contamination in the area of the UST cavity. 5.2 Groundwater Contamination The results from this phase of investigation indicate that a plume of contaminated groundwater underlies this site at a depth of 85 feet. The plume consists of hydrocarbons that are typical of gasoline (including benzene and toluene) , as well as several halogenated hydrocarbons of unknown origin. The limits of the plume have not been determined, but petroleum hydrocarbons in the gasoline range (TPH-g) are limited to monitoring well MW-2 at the present time. Benzene contamination is more extensive, and has ! 9