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Second Quarter 1996 Status Report - Unocal Station No #6981 August 9, 1996 Between March 26 and June 25, 1996 the VES operated approximately 47 days, or 48% of the time (high temperatures caused supplemental blower to overheat shutting VES down) Soil vapor was extracted from wells VW-1, VW-2, and VW-4 through VW-6 during the first quarter 1996, as field monitoring indicated these wells had the highest hydrocarbon concentrations. To optimize VES operation during the June 25 site visit, wells VW-1, VW-3 and VW-6 were shut off (lowest hydrocarbon concentrations) and the system is currently extracting from wells VW-2, VW-4, and VW-5 (highest hydrocarbon concentrations) TPHg destruction efficiencies during this period ranged from 97 46 to 99 50 percent, and benzene destruction efficiencies ranged from grater than 95 00% to 100 00 percent. During the second quarter 1996 the TPHg extraction rate ranged from 11 to 29 pounds per day (lb/day), while the benzene extraction rate ranged from <0 002 to <0 072 lb/day To date, approximately 8,392 pounds of TPHg and 163 pounds of benzene have been extracted and treated by the VES The VES continues to meet all SJVUAPCD permit conditions with regard to hydrocarbon destruction efficiencies and mass discharge rates. To assess the effectiveness of VES operation, GSI evaluated the radius of influence (ROI) generated by VES operation. On May 28 and June 25, 1996, GSI measured the induced vacuum in vapor extraction wells not being utilized for soil vapor extraction These data are summarized in Table 3 Using a vacuum of 0.2 inches H2O as the vacuum where subsurface air flow is sufficient for remediation, the effective ROI from the vapor extraction wells is approximately 60 feet. The estimated ROI is plotted on Figure 2. Well Abandonment GSI abandoned wells MW-3, MW-10, MW-12, and MW-13 on May 3, 1996 This work was performed to facilitate reconstruction of March Lane and Pacific Avenue by the City of Stockton The wells were abandoned by pressure grouting. A Letter Report dated June 3, 1996, which documents the well abandonment activities was previously submitted to the SJCPHS and the CRWQCB THIRD QUARTER 1996 SCHEDULED ACTIVITIES Groundwater monitoring wells at the site will be monitored and sampled Groundwater samples will be collected from all wells during the third quarter sampling. This work will be performed by MPDS and the Quarterly Data Report will be submitted to the appropriate regulatory agencies by MPDS on behalf of Unocal 485502-8 3