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Historic analytical results for concentrations of TPHD in groundwater samples collected from wells MW-1,MW-2,MW-3,MW-5,and MW-6 indicate decreasing concentration trends through time. The intersection of the TPHD trendline for each plot with the TPHD WQO of 100 ug/L(RWQCB, 2004) indicates a reasonable time period for achievement of the WQO. The trendline for historic TPHD concentrations in well MW-5 is relatively flat. However,TPHD concentrations in well MW-5 have been below the laboratory detection limit(<50 ug/L)and the WQO of 100 ug/L (RWQCB, 2004)for the last four quarters of groundwater monitoring without subjecting samples to silica gel L cleanup. Additionally,the historically low concentrations of TPHD detected in groundwater samples from well MW-5 influences the relatively flat trendline. 6.0 Estimated Time to Reach Water Quality Objectives Calculations were performed to estimate the amount of time required to reach the WQO for residual concentrations of TPHD detected in groundwater samples collected in wells MW-1,MW-2, MW-3,MW-5,and MW-6 using the decay rates generated from the Microsoft ExcelTM regression analyses on Figures 8 through Figure 12. The projected time to reach the TPHD WQO for residual TPHD detected in wells MW-1,MW-2, MW-3,MW-5,and MW-6 are presented in Table 5. Table 5 Projected Time to Reach TPHDI WQ02 Western Oil and Sp readin Inc.Acam o Plant Site,Acam o,California Sample Decay Rate3 Final TPHDFactor Concentration Projected Year Location (per year) to Reach WQO (WQO=100u MW-1 -0.1135 1,070.2 100 2021 MW-2 -0.1581 460.09 100 2011 MW-3 -0.2934 538.85 100 achieved MW-5 -0.0136 73.158 100 achieved MW-6 -0.1054 372.09 100 2014 1. TPHD:Total Petroleum Hydrocarbons as Diesel 2. WQO:Water Quality Objective for TPHD=100 ug/L(RWQCB,2004) 3. Decay rate generated by Microsoft ExcelTM regression analyses as shown on Figures 8 through 12 4. Factor generated by Microsoft ExcelTM regression analyses trendline equation as shown Lon Figures 8 through 12 5. ug/L:micrograms per Liter L Trend analyses of historic groundwater analytical results from wells MW-1,MW-2,MW-3,MW-5, and MW-6 indicate that concentrations of TPHD in these wells should reach the WQO of 100 ug/L (RWQCB,2004) within a reasonable time. However,the predicted time required for achievement of WQOs is conservative because the TPHD analytical results prior to any silica gel cleanup procedure were used in the Microsoft ExcelTM regression analyses of TPHD concentrations versus time for wells MW-1,MW-2,MW-3,and MW-6. Groundwater samples subjected to silica gel cleanup from wells MW-1,MW-2,MW-3,and MW-6 have been reported below the TPHD WQO of 100 ug/L- \\Eureka\projects\2007\007152-WOS\PUBS\rpt\20100324-1stHalf2010GWMR&RFC.doc c :2A ! 14