ARCHIVED REPORTS_XR0004566 - Laserfiche WebLink

Home Browse Search

Geological recluucs11K Page 3 Groundwater Monaonng Report Project No 662 2 September 12,2001 ' The groundwater samples collected on August 3, 2001 were delivered to California Laboratory Services of Rancho Cordova, California (Department of Health Services ' Certification No 1233), for the following analyses • Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX) by EPA method 602 ' • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) • MTBE, DIPS, ETBE, TAME and TBA by EPA method 8260 ' The detection limits for the above analyses are listed in Table 2 of Appendix A while the lab analytical results are presented in Appendix B 1 2.0 FINDINGS AND DISCUSSION The results of the groundwater sample analysts show the following • Well MW-1 contained gasoline oxygenates MTBE and TAME at 2500 �tg/l and 13 µg/l, ' respectively • Well MW-3 contained gasoline oxygenates MTBE, ETBE and TAME at 6600, 9 0 and 24 µg/l, respectively • MW-2, which is upgradient of the former USTs, has not contained contaminant concentrations above the laboratory for the seven quarterly events completed thus far in the investigation • Neither BTEX nor TPH-G was present in any of the groundwater samples above the laboratory reporting limits ' . Oxidation-Reduction Potential measurements (Table 3) show that well MW-3 has a negative value This suggests that MW-3 is within the halo of reaction-depleted water caused by biodegradation of the contaminants The values for wells MW-1 and MW-2 ' are still positive, suggesting that there is a limited amount of biodegradation of the contaminant plume occurring This is to be expected, since the primary contaminant is MTBE, which is very resistant to biodegradation The lateral extent of the contamination is only defined upgradient to the northwest by MW- ' 2 The vertical extent has not been defined GTI makes the following recoimnendations • Perform plume definition and evaluate the mass of contaminants present by installing additional monitoring wells GTI proposes the installation of two additional monitoring wells, MW-4 and MW-5, in the locations indicated in Figure 4 Well MW-4 will be located in the predominant down gradient direction as shown in Figure 3 — Groundwater Gradient Rose Diagram Well MW-5 will be placed to the north of the site in the direction of the highest recorded groundwater gradient (a magnitude of 0 018