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Monitoring—March 29-31,2006, 7500 West Eleventh Street, Tracy, CA Page 20 Report: Groundwater-quality g 5.4 Data Sufficiency Confirmation The MAROS software also provides for an evaluation of the available groundwater- quality database to support the statistically-developed findings generated by the algorithms. This allows the user to assess whether, given the observed variability of the concentrations of analytes of concern in samples of groundwater recovered from the wells, the degree of confidence with which the plume stability, sampling frequency and other program output parameters the can be relied upon. If the distribution of wells is insufficient to characterize adequately the plume of groundwater or if the number of sampling rounds is insufficient to demonstrate reliably the trends in concentrations of analytes of concern with time, the data sufficiency analyses indicate that there is low confidence in the plume stability or sampling frequency recommendations. Conversely, if the well array geometry and sampling frequency are sufficient to support an accurate statistical evaluation of conditions within the plume, the data sufficiency analyses assign a high degree of confidence to the results of the MAROS output. The Regression of Plume Centerline Concentrations table in Appendix A indicates the coefficients of confidence for the MAROS analysis of each of the BTEX compounds in groundwater in wells along the centerline of the primary plume at the Navarra Site for the total of 21 groundwater-quality monitoring rounds that have been conducted at the site over the period May 11, 2000 to March 31, 2006. A striking feature of that Table is the zero confidence computed for results generated by statistical analysis of the first five y;. rounds of groundwater-quality monitoring at the site that were conducted over the period May 2000 to December. 2001. However, completion of the next groundwater-quality monitoring round, on April 11, 2002, caused the confidence in the data for each of the BTEX compounds to increase to well over 65%. The reason for the total lack of statistical confidence in the ability of the groundwater- quality data gathered prior to April 11, 2002 to characterize adequately the primary plume of affected groundwater at the Navarra Site is the inadequacy of the array of groundwater-quality monitoring wells that had been installed prior to that time. From the time the subsurface beneath the 7500 West Eleventh Street Site was opened to exhume the underground storage tanks, it was evident to SJC, based on simple observation of the hydrogeological properties of the subsurface soil and the gross nature of the contamination that, at that time, affected the groundwater, and would also have been ; evident to any California-licensed geotechnical engineer, that affected groundwater had migrated well to the north of West Eleventh Street. Consistent with those observations, SJC's initial Work Plan for site characterization of the Navarra Site called for installation of monitoring wells along Chrisman Road to the north of West Eleventh Street (The San Joaquin Company 1999). However, SJCEHD, which, at that time, employed no staff licensed by the State of California to practice either engineering or geology, as is required by California law, advised the California Underground Storage Tank Cleanup Fund (USTCF) to deny funding for that work (California Underground Storage Tank Cleanup Fund 2000). This action caused a delay in the installation of monitoring wells to the north of West Eleventh Street until April 2002. As is shown in. Appendix A, when the previously-prohibited wells were installed and samples were recovered from them, the sic