ARCHIVED REPORTS XR0011755 - Laserfiche WebLink

Home Browse Search

Evaluation of Natural Attenuation_ 7500 West Eleventh Street, Tracy, CA. Page 4 in the interior of the plume of affected groundwater emanating from the 7500 West `! 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 same array of wells was again checked for the presence of floating product on July 26 and October 27, 2004, The historical record of LNAPL thickness measured in the array of floating product monitoring wells through October 27, 2004 is presented in Table 3. Table 3 also includes the results of measurements of LNAPL thickness in the array of floating product monitoring wells that was conducted on February 24, 2005 in association with the evaluation of natural attenuation conducted on the site. i 1.3.4 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 and third rounds of sampling and analysis of the water produced from those wells were conducted on July 27 and October 28, 2004. This report includes the results of the fourth quarterly monitoring round of that program, which was conducted on February 25, 2005. The results of those four sampling rounds are recorded in Table 4. 1.3.5 Recommendations for Evaluation of Natural Attenuation r ' Based on our extensive experience with fuel hydrocarbon contamination at sites similar 1= to the Navarra Site, by December 2003, it was clearly apparent to SJC that the historical results of the groundwater-quality evaluation program that had been on-going since May 2000 indicated that natural processes were acting to significantly attenuate the = concentrations of chemicals of concern at the 7500 West Eleventh Street property. Accordingly, as we have done on many other occasions (2004c, 2004e, 2003e, 2002a, c); SJC reconunended that the scope and frequency of the groundwater-quality monitoring program be revised to reduce unnecessary expense to the California Underground Storage Tank Cleanup Fund (USTCF), while maintaining sufficient elements of the monitoring program to ensure that some unexpected behavior of the groundwater plume did not '- ' develop and increase risks to the environment of the site and its adjacent areas. SJC proposed that an evaluation of natural attenuation of contaminants in groundwater be conducted based upon a formal assessment of primary and secondary evidence. That proposal, which was supported by an engineer's estimate of the cost of its implementation, was included in SJC's work plan for refinedplume definition and .� management of floating product (The San Joaquin Company Inc. 2003a) and reiterated in the October 2004 quarterly groundwater-monitoring report (The San Joaquin Company Inc. 2004b). Finally, at a meeting requested on December 15, 2004 by SJC and held at the Stockton offices of the SJCEHD on January 18, 2005, attended by representatives of the SJCEHD, the RWQCB and SJC, the staff of the regulatory agencies requested that a formal evaluation of natural attenuation at the Navarra Site be performed. The groundwater sic J