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Station #11194 <br /> Quarterly Groundwater Monitoring Report (1 Q2006) <br /> April 28, 2006 <br /> Page 4 <br /> MtBE was 6 1 NgIL (MW-6) Other analytical concentrations were generally consistent with <br /> previous sampling events <br /> This report is based on data, site conditions, and other information that are generally applicable <br /> as of the date of the report, and the conclusions and recommendations herein are therefore <br /> applicable only to that time frame <br /> Groundwater analytical results for benzene, TPHg and MtBE dissolved in groundwater are <br /> presented on Figure 4 and are summarized in Table 1 <br /> Dissolved MtBE Distribution <br /> The constituents of concern at the site include dissolved MtBE Concentrations of MtBE have <br /> historically been detected in the majority of the site wells, with the highest concentration during <br /> the first quarter 2006 reported in well MW-6 at 6 1 pglL This concentration is and increase from <br /> fourth quarter 2005 when it was below laboratory reporting levels MtBE levels did not change <br /> between sample dates in fourth quarter 2005 and first quarter 2006 at wells AMW-5 and MW-7 <br /> MtBE levels decreased in two wells (AMW-3 and MW-4) between fourth quarter 2005 and first <br /> quarter 2006 Concentrations of MtBE were below laboratory reporting limits at well AMW-5 <br /> Dissolved TPHg Distribution <br /> The maximum concentration of TPHg detected in first quarter 2006 was 920 NgIL (MW-6), which <br /> is a decrease from the level detected in fourth quarter 2005 (2,700 pg/L) Two other monitoring <br /> wells displayed TPHg above the laboratory reporting limit (AMW-3 and MW-4) at 18 33 pglL and <br /> 240 pg/L, respectively The remaining wells (AMW-5, AMW-6, and MW-7) did not display <br /> concentrations at or above laboratory reporting limits in first quarter 2006 <br /> Monthly Groundwater Sampling <br /> Monthly groundwater samples were collected by Blaine Technical Services from monitoring <br /> wells MW-1 through MW-7, and were submitted to Sequoia Analytical for analysis for GRO, <br /> BTEX, MtBE, and TBA by EPA Method 8260B During the first quarter 2006, groundwater <br /> samples were collected from the wells on January 26, 2006 Results of the monthly <br /> groundwater sampling events are summarized in Table 1 <br /> Based on discussion with the San Joaquin County Environmental Health Department, additional <br /> vertical delineation will be performed for this site Further details will be included in a work plan <br /> addendum to be submitted during 2006 At the present time, additional lateral investigation will not <br /> be conducted <br /> 11BP-ARC0105 BP-COP Sites1111941Reports\Q1V1Rs111194 1QO6 QMR doc SECOR International Incorporated <br />