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1 9 <br /> o Cambria evaluated water-level measurement data and prepared a groundwater contour <br /> map (Figure 2) Groundwater flow is generally to the east at an approximate <br /> hydraulic gradient of 0 01 <br /> o TPHg and benzene were not detected in any of the groundwater samples MTBE (by <br /> EPA Method 8020) was reported in wells MW-1, MW-2, MW-5, VEW-1, VEW-2, <br /> and VEW-4 at concentrations ranging from 9 43 to 2,050 ppb An EPA Method <br /> 8260A confirmation analysis confirmed the presence of MTBE in MW-5 at a <br /> concentration of 2,220 ppb (although the analysis was run one day past the hold <br /> time) A chemical concentration map is presented on Figure 2 <br /> Quarterly Sampling <br /> Groundwater samples were analyzed for total purgeable hydrocarbons as gasoline (TPHg) by <br /> EPA Method 8015 (Modified) and benzene, toluene, ethylbenzene, xylenes (BTEX), and <br /> methyl tertiary butyl ether (MTBE) by EPA Method 8020 An EPA Method 8260A <br /> analysis was also performed on the groundwater sample from MW-5 Groundwater samples <br /> from well VEW-3 was also analyzed for halogenated volatile organics by EPA Method 8010B <br /> (Table 1) <br /> Field monitoring data and chemical analytical data are presented in a summary table in <br /> Blaine's groundwater monitoring report (Appendix A) Additional groundwater analytical <br /> data is summarized on Table 1 <br /> Conclusions and Recommendations <br /> TPHg. and benzene concentrations have been at low or non-detect levels at this site for <br /> several quarters MTBE detected at this site is suspected to be from an offsite source MTBE <br /> levels are highest in the upgradient well at this site and in a well that is upgradient of possible <br /> source areas on the former Shell site Additionally, MTBE levels in upgradient well MW-5 <br /> have been steadily increasing Since this service station has not been in operation since <br /> 1990, it is unlikely MTBE detected in site wells is due to a release from the former Shell site <br /> Cambria previously recommended groundwater monitoring and sampling be discontinued as <br /> there is little benefit to collecting additional data at this site Cambria also recommended <br /> closure be pursued for this site SJCPHS contacted Cambria on March 21, 2000 and requested <br /> • we continue quarterly monitoring due to the MTBE levels detected in our wells <br /> 0821 2 <br />