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Fortner Beacon Station 494 October 8, 1996 Stockton, California Appendix B Closure Report Conclusions contained in the report recently prepared for the State Water Quality Control Board (SWQCB) by the Lawrence Livermore National Laboratory (LLNL) entitled Recommendations to Improve the Cleanup Process for California's Leaking Underground Fuel Tanks, indicated that intrinsic bioremediation processes may be degrading hydrocarbons sufficiently to limit the length migration potential of the petroleum hydrocarbons in the subsurface soils and groundwater As a result of flus report, a memo dated November 8, 1995 was issued by Mr Walt Pettit of the SWQCB which indicated agencies should identify and aggressively close sates that were considered "low risk" Based on the current levels of hydrocarbons remaining in the soil and groundwater at this site, it is our opinion that Former Beacon Station No 494 qualifies as a low-risk site and should be closed In summary, Horizon believes this site should be closed based on the following • Concentrations of gasoline-range hydrocarbons have been reduced by over 98% of the total mass estimated to have initially existed in the soil and groundwater • Additional effort for remediating remaining residual gasoline-range hydrocarbons to background levels is neither economically feasible or practicable It is estimated that approximately 181 lbs of TPHg (29 gallons) and possibly no detectable benzene remain in soil and an unmeasurablely small amount of TPHg and benzene remains dissolved in groundwater When shutdown was effected, Best Available Technology for thus site had been employed, and concentrations were no longer being reduced proportional to effort • The depth of gasoline-range hydrocarbons left in place in soul and groundwater and expected site usage (paved commercial) and local water usage make it very unlikely that 1494 APB 14 HORIZON ENVIRONMENTAL INC