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Former Beacon Station 494 October 8, 1996 <br /> Stockton, Califorma Appendtx B Closure Report <br /> Control Board (CRWQCB) contains guidelines for evaluating sites for regulatory closure <br /> The WQCP states in Chapter 4, Section 9 0) that soil cleanup levels are to be based on <br /> background concentrations of the individual constituents unless the background levels are <br /> technologically or economically infeasible It further states that where background <br /> concentrations are unfeasible to achieve, soil cleanup levels are to be established to ensure <br /> that remaining constituents of concern will not cause groundwater to exceed the applicable <br /> groundwater cleanup standards or pose a threat to human health or the environment <br /> Based on all the data gathered, it is Horizon's professional opinion that Ultramar has utilized <br /> the Best Available Technology to remove significant concentrations of gasoline-range <br /> hydrocarbons from the soil underlying the site Calculations used to equate known <br /> concentrations of TPHg initially in soil and the amount removed show that the vapor <br /> extraction system removed a larger volume of TPHg than was initially discovered It should <br /> be noted that further reducing petroleum hydrocarbon concentrations in soil to background <br /> concentrations is not be economically or technically feasible <br /> The WQCP further states in Chapter 4, Section 9 (g) that groundwater cleanup levels are to <br /> be based on background concentrations, water quality objectives, risk to human health and <br /> the environment, and the technologic and economic feasibility of attaining background <br /> concentrations At this time, benzene concentrations are present slightly above the State <br /> Maximum Contamination Level only in monitoring well MW-3 (12 ug1L) in the <br /> approximate center of the site This well has previously fluctuated to lower concentrations <br /> and below detection limits for hydrocarbons It would not be technologically or <br /> economically feasible for Ultramar to continue to pump groundwater to attempt to recover <br /> this amount of contaminant Furthermore, since the public water supply or any wells in the <br /> area do not draw from as a source, the uppermost groundwater, the remaining hydrocarbons <br /> pose no significant risk to human health or the environment <br /> 1494 APB <br /> 13 HORIZON ENVIRONMENTAL.INC <br />