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URS <br /> Mr. Robert McClellon <br /> January 31,2011 <br /> Page 4 <br /> California State Action Level for Drinking Water is established for vanadium at 0.05 mg/L. For the <br /> remaining constituent,the Agricultural Water Quality Limits is established at 0.05 mg/L for cobalt. <br /> Secondary MCLs are established for TDS at 500 mg/L by EPA and DHS and specific conductance at <br /> 900 pmhos by EPA. The dissolved metal results,TDS results, and field measurements are summarized <br /> in Table 2. <br /> The analytical report is provided as Attachment 2. <br /> CONCLUSIONS AND RECOMMENDATIONS <br /> Nine metals(arsenic,barium, chromium,cobalt, iron,manganese,nickel,vanadium and zinc)and TDS <br /> were detected above the analytical reporting limits in the groundwater samples collected on <br /> December 16,2010. Of these constituents, five(arsenic, barium, iron, manganese,and TDS)were <br /> above their respective established regulatory levels.Because four of the metal results and TDS were <br /> above their respective established regulatory levels,URS plans to continue monitoring of these metals <br /> and TDS. Because the results have not changed significantly since the start of the quarterly groundwater <br /> monitoring in December 2006, URS recommends that monitoring continue on an annual basis. <br /> Prior to the installation of the passive soil vapor extraction trench,the methane concentration <br /> historically exceeded 5%by volume within the following probes: VW-4,VW-5S, VW-5D,VW-6S, and <br /> VW-6D. Since the passive soil vapor extraction trench installation in September 2006,the methane <br /> concentration has decreased within these probes to less than 5%by volume during the following quarter <br /> and has continued to be less than 5% by volume during the subsequent quarters. Methane concentrations <br /> measured within all probes during 4Q10 were less than 5%by volume. <br /> Based on the results during this quarter,compared to the results prior to the passive soil vapor extraction <br /> installation,the passive soil vapor extraction trench appears to be effective at controlling methane from <br /> leaving the site. Because the results of the monitoring activities for measuring landfill gas <br /> concentrations within the probes have been less than 5%by volume since December 2006(following <br /> the installation of the passive soil vapor extract trench),we recommend that the monitoring activities <br /> continue on an annual basis. <br /> Should you have any questions regarding this report,please contact me at(916) 679-2081. <br /> Very truly yours, <br /> URS <br /> Ja Kamine <br /> S n' r Civil Engineer <br /> H:\Wprocess\25532\WorldEnterprise\Quarterly Rpt\2010\4Q10\012011 doc <br />