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ARCADIS 2010/2011 Annual <br /> Monitoring Report <br /> Union Pacific Railroad <br /> Company <br /> Tracy, CA- Maintenance <br /> � <br /> Groundwater gradients were not calculated for the C-Zone due to limited data. Facility <br /> 5.2 Free-Phase Product Observations and Measurements <br /> Measureable free-phase product was observed during the 2010/2011 reporting period <br /> in eight wells (MW-06A, MW-08A, MW-11A, PZ-01, PZ-02, TW-01, TW-02, and <br /> TW-04). The product thicknesses in these wells ranged from approximately 0.24 <br /> inches (PZ-02)to 25.44 inches (PZ-01). Table 2 presents a summary of product <br /> measurements and the estimated product thicknesses. Figure 7 presents the product <br /> thickness measurements recorded since May 2001. <br /> As shown in Table 1, groundwater elevations in source area wells MW-2A, -10A, -12A, <br /> and-14A have increased approximately three feet(from approximately 40 feet msl to <br /> approximately 43 feet msl)since 2008. Consequently, groundwater has contacted <br /> residual LNAPL, present in formerly unsaturated sediments, resulting in localized <br /> LNAPL mobilization and apparent increases in LNAPL thickness observed in source <br /> area wells. The total volume of LNAPL in the subsurface has not increased because <br /> there is no new source of LNAPL at the site. In addition,the stability of the dissolved- <br /> phase plume extent and concentration trends during this time frame suggests that the <br /> apparent increase in LNAPL thickness in source area wells has not contributed to <br /> plume expansion. <br /> 5.3 TEPH Analytical Results <br /> TEPH-d and historical TEPH-d with Silica Gel cleanup (SG)concentrations in <br /> groundwater samples collected since February 2001 are presented in Table 3. March <br /> 2011 TEPH-d concentrations in A-Zone groundwater samples are shown on Figure 8. <br /> 5.3.1 A-Zone <br /> TEPH-d was detected above Cleanup and Abatement Order(CAO) No. 92-707 <br /> cleanup level of 100 micrograms per liter(pg/1) in samples collected from ten of 19 <br /> monitoring wells sampled during the 2010/2011 reporting period. Detected <br /> concentrations ranged from 60 pg/I at MW-23A located approximately 100 feet south of <br /> the engine house to 1,200 pg/I at TW-03 located along the northern edge of the engine <br /> house and were generally consistent with previous analytical results. <br /> final_ta y,.-maint fadlity_AnnRpt_4-26-2011.d- Page:4/7 <br />