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1 <br /> Report:Groundwater-quality Monitoring—March 29-31,2006, 7500 West Eleventh Street, Tracy, CA Page 30 <br /> 1 <br /> product have been detected in the well but, at the time of the March 2006 monitoring <br /> round, only a trace of LNAPL, with a thickness of less than 0A1 ft., was present in that <br /> well. <br /> Given the conditions stated above, we recommend that future LNAPL monitoring be <br /> limited to checking for the presence of floating product in Monitoring Well MW-7. The <br /> monitoring should be conducted semiannually, in July and January of each year, at which <br /> time any LNAPL that might have accumulated will be purged from the well. <br /> 8•4 Potable Water-quality Monitoring Program <br /> Since the quarterly program of potable water quality monitoring was initiated on April 1, <br /> 2004, no detectable concentrations of any analytes of concern have been detected in any <br /> sample of groundwater recovered from any of the monitored potable water supply wells. <br /> Over the same period, the plumes of affected groundwater at the site have remained <br /> stable and contaminants of concern in the groundwater have been oscillating around a <br /> .declining trend. The extensive site characterization work and groundwater monitoring <br /> program conducted on the Navarra Site have demonstrated that affected groundwater is <br /> a <br /> limited to the first shallow aquifer, which has its base at approximately 25 ft. BGS, and, <br /> therefore, the groundwater affected by components of petroleum hydrocarbons is located <br /> well above the zone from which the potable water supply wells extract water. For <br /> example, the potable water well at 2390 South Chrisman Road has a total depth of 325 <br /> ft., the casing is perforated between 297 ft and 325 ft. BGS, and the annular space <br /> between the casing and the boring wall is sealed with bentonite from the ground surface <br /> to a depth of 50 ft. The filter pack extends from 275 ft. to.325 ft. BGS. <br /> Given the conditions described above, SJC believes that monitoring of the potable water <br /> supply wells can now be discontinued without posing any risk to the consumers of the <br /> potable water extracted from those wells. Accordingly, SJC recommends that, to save <br /> future unnecessary expenditure by the California Underground Storage Tank Cleanup <br /> Fund (USTCF), the potable water monitoring program be discontinued, effective <br /> immediately. <br /> sic <br />