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Mr. John MacLeod -2 - <br /> Chevron <br /> 2 -Chevron Corral Hollow and Gran\,,.,,e Road, Tracy 9 February 2010 <br /> 1 March 2010, Chevron needs to notify Central Valley Water Board staff if it intends to <br /> drill a soil boring at this location to evaluate current soil concentrations. <br /> 3. The Report states that Chevron believes the water quality objective (WQO) for TPHg is <br /> 100 micrograms per liter (pg/L) and not 5 pg/L. Central Valley Water Board staff does <br /> not agree. As stated in our 17 September 2009 letter, the 15 September 1998 Water <br /> Quality Control Plan for the Sacramento and San Joaquin River Basins, Fourth Edition <br /> (revised September 2009) considers all groundwater to be a potential drinking source. <br /> State Water Resources Control Board Resolution No. 92-49 requires cleanup to <br /> background concentrations, if technically and economically feasible. Since petroleum <br /> hydrocarbons do not naturally occur at this Site, the cleanup level for all petroleum <br /> hydrocarbons is nondetectable at normally-achievable laboratory method detection <br /> limits. Since the normally-achievable detection limit for TPHg is 50 pg/L, this becomes <br /> the default WQO. Thus, the applicable WQOs for Corral Hollow COCs include <br /> 100 pg/L for TPHd, 50 pg/L for TPHg, and 17 pg/L for naphthalene. <br /> 4. The 17 September 2009 Central Valley Water Board staff letter notified Chevron that <br /> the Site cannot be considered for unrestricted closure until Chevron shows the <br /> groundwater concentrations will reach WQOs within a reasonable timeframe and soil <br /> concentrations are below gross contamination levels. Chevron needs to continue to <br /> monitor the Site according to Monitoring and Reporting Program No. R5-2006-0804. <br /> Chevron may consider closing the Site with a deed restriction that would restrict the <br /> use of Site groundwater and soil. <br /> In summary, by 1 March 2010, Chevron needs to notify Central Valley Water Board staff if it <br /> intends to drill a soil boring near SB-8. In addition, by 30 April 2010 Chevron needs to drill the <br /> four soil borings, analyze soil and grab groundwater samples, and submit a report of findings. <br /> Prior to Site closure, Chevron needs to show that groundwater concentrations will reach WQOs <br /> within a reasonable timeframe and soil concentrations are below gross contamination levels. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4819 or <br /> kshelton(a waterboards.ca.gov. <br /> KRISTI SHELTON, P.E. <br /> Water Resources Control Engineer <br /> Aboveground Tanks Cleanup Unit <br /> cc: San Joaquin County Environmental Health Department, Stockton <br /> Mr. Allen Just, ARCADIS, Irvine <br />