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Report:Groundwater-quality Monitoring—March 29-3I 2006, 7500 West Eleventh Street, Tracy, Cry .Page 16 5.4 GROUNDWATER MONITORING PROGRAM OPTIMIZATION STUDY E ' ' Following the round of groundwater-quality monitoring conducted in the period February 24-March 16, 2005, SJC completed a comprehensive groundwater monitoring optimization study. The scope of that work included application of the Monitoring and Remediation Optimization System (MAROS) (United States Air Force 2004), use of which is advocated by both the United States Environmental Protection Agency (US- EPA) and the California Environmental Protection Agency (Cal-EPA) (United States Environmental Protection Agency 2005). The results of that MAROS analysis, which considered the complete compilation of groundwater-quality data gathered through March 2005, indicated that an efficient groundwater-quality monitoring program for the 7500 West Eleventh Street Site would require a recovery of samples on either an annual or biennial sampling frequency from the great majority of the wells at the site. The exceptions were Monitoring Wells MW-3, MW-7 and MW-13, for which the optimization study results called for continued quarterly monitoring until such time as the statistical trend in the concentrations of analytes of concern in groundwater in those wells could be established reliably(The San Joaquin Company 2006d). Although, based on the earlier MAROS analysis, such was not required, over the period June 2005 through March 2006, SJC continued to monitor on a quarterly basis the concentrations of analytes of concern in Monitoring Wells MW--3, MW-4, MW-5, MW- 7, MW-10, MW-11, MW-12, MW-13, MW-16, MW-17, MW-18, MW-19, MWFP-1, -ti MWFP-2, MWFP-4 and MWFP-5. The data gathered from those sampling rounds was used to extend the groundwater-quality database for the Navarra Site. At the completion of the March 2006 groundwater-quality monitoring round, a second MAROS analysis was made for the 7500 West Eleventh Street Site using the complete set of groundwater-quality data compiled through that time. The principal results are summarized below. The output from the analytical software is presented in Appendix A. 5.1 MAROS Input Data The geochemical data input required for the MAROS evaluation is closely similar to the historical groundwater chemistry data presented in Table 2. However, the MAROS software also permits analytical results taken from samples recovered at different times but that were separated by only a few days to be treated as though they were obtained from samples recovered on a single date. This permits data from a sampling round that required more than one day to complete to be treated analytically as a single event. In addition for theose u of the MAROS analysis, SJC opted for the concentrations of p � Y p analytes recorded by the laboratory as "not detected" to be set at 50% of the method detection limit (MDL). The MAROS analysis requires the locations of all wells in the monitoring well field to be defined by coordinates. Because it is situated adjacent to the northern boundary of the J Cf . pump island of the former fueling station and on the axis of the principal plume of contaminated groundwater, SJC set the origins of the coordinates at Monitoring Well SJC