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Between March 2004 and May 2018 , soil vapor extraction/air sparging was used as a remedial <br /> technology to remove petroleum hydrocarbons from the soil . Approximately 182 , 753 pounds of <br /> total petroleum hydrocarbons as gasoline range organics ( GRO) were removed from the <br /> subsurface , including 1 , 060 pounds of benzene , and 100 pounds of methyl tertiary butyl ether <br /> ( MTBE ) . <br /> Remediation and natural attenuation have significantly reduced petroleum hydrocarbons in soil and <br /> groundwater at the site to concentrations below the California State Water Resources Control <br /> Board ' s Low-Threat Underground Storage Tank Case Closure Policy ( LTC Policy) screening <br /> levels . It is estimated that GRO and benzene concentrations will reach water quality objectives by <br /> the end of 2020 . Additionally , the results of the confirmation soil sampling completed in October <br /> 2018 near historical borings with previously elevated petroleum hydrocarbon concentrations <br /> confirmed that impacts have been sufficiently remediated , and petroleum hydrocarbons have been <br /> removed to the extent practicable . <br /> The remaining hydrocarbon impacts to subsurface soil and groundwater do not appear to pose any <br /> significant threat to human health , the environment , or future site activities . Due to the low threat <br /> posed to human health , this site has been recommended for closure by Arcadis U . S . , Inc . under <br /> California ' s LTC Policy . Once all public comments have been reviewed , the Central Valley Water <br /> Board will consider closing the case . <br />