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1 " Report: Groundwater-quality Monitoring—March 29-31,2006, 7500 West Eleventh Street, Tracy, CA Page 4 performed on November 28, 2000, no MTBE was detected in the samples recovered from Monitoring Well MW-7. It is believed that this does not indicate that, by that time, the groundwater in the vicinity of that well was free of MTBE. Rather, it indicates that the high concentrations of other components of fuel hydrocarbons were such as to raise the method detection limit of the MTBE analysis to a level greater than the concentration of that analyte actually present in that groundwater sample. r,. By April 11, 2002, it was clear that floating product was present in the surface of the groundwater in Monitoring Well MW-7. It continued to be present at various apparent thicknesses up to 0.58 ft. until an LNAPL-purging program in that well was initiated on .. November 8, 2003. As part of the further extension of the site characterization program in April 2004, five floating product monitoring wells were installed at the locations shown on Figure 2 to investigate the down-gradient extent to which LNAPL may have migrated in the interior of the plume of affected groundwater emanating from the 7500 West LE Eleventh Street property. The thickness of floating product in those five wells was checked at that time and tests were also made to detect the presence of LNAPL on the - water table in groundwater-quality monitoring wells MW-7, MW-13 and MW-14. The Lsame array of wells was again checked for the presence of floating product on July 26 and October 27, 2004, and on February 24, June 23, October 20, and December 20-21, 2005. The historical record of LNAPL thickness measured in the array of floating product monitoring wells through March 2006 is presented in Table 3. 1.3-4 Evaluation of Natural Attenuation In addition to the groundwater-quality monitoring round that was conducted in February and March 2005, an extensive program of field testing, laboratory analysis and geochemical and engineering studies was completed to investigate the progress of natural attenuation processes that are reducing the contaminant load in groundwater beneath the Navarra Site. That work demonstrated that there is strong primary and secondary evidence that natural attenuation is aggressively reducing contaminant concentrations in the subsurface and that those processes alone will be sufficient to adequately remediate the groundwater within a reasonable time, which is estimated to be on the order of 10 to 20 years (The San Joaquin Company Inc. 20064). 1.3.5 Testing of Water in Potable Water-supply Wells At the direction of the SJCEHD, the quality of water in six potable water-supply wells in ` the neighborhood of the Navarra Site was analyzed in April 2004. Second, third and fourth rounds of sampling and analysis of the water produced from those wells were conducted on July 27 and October 28, 2004 and on February 25, 2005. In accordance with SJC's recommendation, which was approved by the SJCEHD following the completion of the round of monitoring conducted on February 25, 2005, the scope of the potable water supply monitoring program was reduced to three wells. This report includes the results of the eighth quarterly monitoring round of that program. SJC