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Sloop, <br /> `r Second Semiannual 2011 Groundwater Monitoring Report <br /> Former Texaco Service Station <br /> Chevron Site ID 309075 <br /> February 28, 2012 <br /> • Methyl tertiary butyl ether (MTBE), tertiary butyl alcohol (TBA), di-isopropyl ether (DIPE), <br /> ethyl tertiary butyl ether (ETRE), tertiary amyl methyl ether (TAME), <br /> 1,2-dichloroethane (1,2-DCA), ethylene dibromide (EDB), also known as <br /> 1,2-dibromoethane, and ethanol by USEPA Method 8260B <br /> • Methanol by USEPA Method 8015B <br /> The laboratory analytical report and chain-of-custody record for the semiannual groundwater <br /> sampling event are included in the Lancaster analytical results package (Attachment C). <br /> 4.3 Remedial System Status <br /> A remedial system is not associated with the site. <br /> 4.4 QA/QC <br /> Quality assurance/quality control (QA/QC) samples, inclusive of trip blanks, were submitted for <br /> laboratory analysis. A laboratory supplied trip blank accompanied each sample delivery group. <br /> Trip blank samples were analyzed for TPH-GRO, BTEX and MTBE. <br /> r. <br /> 5.0 DISCUSSIONS, CONCLUSIONS AND RECOMMENDATIONS <br /> 5.1 Discussion <br /> 5.1.1 Groundwater Monitoring Results <br /> Depth-to-water measurements were subtracted from surveyed top of casing elevations to <br /> calculate the groundwater elevation at each monitoring well. Depth-to-water measurements and <br /> calculated groundwater elevations are presented in Table 1.1. Calculated groundwater elevation <br /> data was used to construct a groundwater elevation contour map of the site, presented as <br /> �. Figure 3. <br /> Groundwater elevations across the site ranged from 21.20 (MW-2) to 21.33 (MW-4) feet below <br /> 'r mean sea level (BMSL). On average, groundwater elevations at site monitoring wells increased <br /> 0.15 foot from the first semiannual 2011 monitoring event. The groundwater flow direction <br /> across the site was toward the east-northeast at an approximate horizontal hydraulic gradient of <br /> 0.001 foot per foot (ft/ft), as shown on the groundwater elevation contour map presented as <br /> Figure 3. The predominant historical groundwater flow directions across the site have been <br /> toward the southwest and east-northeast, as depicted on the groundwater flow direction rose <br /> diagram presented as Figure 1 of Attachment D. The groundwater elevation at MW-61D was not <br /> consistent with other groundwater elevations; therefore, the groundwater elevation was not used <br /> for contouring nor was it included in the results presented above. <br /> g:\aproject\env\chevron\309075\6 deliverables\periodic Mon itoring\2011\2sa11\temppdNeut\309075 2sa11 gmr tin 02282012.doc 4 <br />.wr <br />