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i Summary/Conclusions Based on the water level gauging and groundwater sampling conducted during August 1996,the following summary points are provided below: / • Water levels are approximately 60 feet bgs which is approximately 17 feet higher than J when groundwater monitoring was initiated at the Disco property in 1991. The current water levels are approximately 6 to 10 feet above the monitoring well well-screens. I 1 • The AS/SVE system operated from February 1995 through February 1996 removing approximately 9,000 pounds of TPH as gasoline from the source area. However,due to J the rise in water levels above the SVE well screens,the AS/SVE system is currently inoperable. •��' BTEX and TPH as gasoline concentrations continue to remain stable in the plume area g .-4> ,a �Vand are more than an order of magnitude below the concentrations that existed prior to operation of the AS/SVE system. _Zb BTEX and TPH as gasoline concentrations continue to remain non-detectable in the monitoring areas near the fringe of the plume. ��' • MTBE was not detected in any of the monitoring wells sampled. • The ITB demonstration continues to indicate the presence of gasoline reducing constituents in the groundwater including dissolved oxygen,sulfate,nitrate,and ferrous iron. Based on simple calculations,it appears that ITB is capable of stabilizing or reducing the plume. This finding is supported by the Lawrence Livermore National Laboratory study (Recommendations To Improve the Cleanup Process for California's Leaking 04 Underground Fuel Tanks, October 16, 1995)which states that plume concentrations greater than 10 Rg/L benzene extend no more than about 250 feet in 90% of the leaking o underground tank cases. If ITB is selected as the final remedy for the Disco property,it is recommended that groundwater monitoring be conducted for an extended period of time to confirm plume stability and/or reduction. Future Activities/Recommendations • The ITB data collected during the one year demonstration adequately describes the biochemical potential for degradation of gasoline constituents at the Disco property, and no further ITB sampling is necessary. • Del Monte is planning to submit a work plan for final site characterization activity based on recent discussion with PHS staff. • Quarterly monitoring should be discontinued until new wells have been constructed with a screen interval that intersects the water table. I I SFO/G:IP ROJECTSM ELMONTEIPLANT_331QR PT2_971QTR_REP.COC 17 1,