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ARCADIS 2010/2011 Annual <br /> ' Monitoring Report <br /> Union Pacific Railroad <br /> ' Company <br /> Tracy, CA-Maintenance <br /> Dissolved iron, dissolved manganese, nitrite, ammonia nitrogen, sulfide, BOD, COD, Facility <br /> ' and carbon monoxide were not detected above laboratory reporting limits in the A-zone <br /> monitoring wells during the 2010/2011 reporting period. <br /> ' 5.6 Concentration Trends <br /> Figure 9 shows the lateral extent of TEPH-d in the A-Zone since 2006. The March <br /> 2007 samples were not analyzed for TEPH-d because of sampling error by the <br /> ' subcontractor. TEPH has stabilized within the boundaries of the site and <br /> concentrations have declined or remained stable in A-Zone monitoring wells around <br /> the perimeter of the plume. Seasonal TEPH-d concentration increases were observed <br /> ' in A-Zone monitoring wells MW-22A and MW-25A between the March 2011 and <br /> November 2010 groundwater monitoring events, likely due to seasonal influence. <br /> 6.0 Remedial Activities Summary <br /> There are two non-operating remediation systems present at the Site: the source area <br /> ' dual-phase extraction(DPE)treatment system and the margin pump-and-treat <br /> extraction system. The DPE treatment system was shut down in July 2002 and the <br /> pump-and-treat system was shut down in May 2004. The associated Waste Discharge <br /> ' Requirements(No. 98-213)was rescinded in a letter submitted to UPRR by the <br /> RWQCB dated May 22, 2009. <br /> ' Free-product removal activities were not conducted during the 2010/2011 monitoring <br /> period. Previous attempts of free-product removal were ineffective. UPRR and the <br /> RWQCB are discussing whether additional attempts at free product recovery or <br /> implementing other remedies are warranted at the Site. <br /> 7.0 Summary and Planned Activities <br /> Based on evaluation of the groundwater sampling data: <br /> • Dissolved-phase TEPH-d in the A-Zone is laterally well defined, remains stable, <br /> ' and local to the source area(Figure 8). <br /> • Free-phase product continues to be observed in monitoring wells located within the <br /> source area, with measurable thicknesses up to 25 inches. <br /> • TEPH-d was detected in wells MW-11 BR(56 pgll), MW-12B(220 pg/1), and MW- <br /> 01C(230 pg/l)during the March 2011 monitoring event that had previously been <br /> ' final tai".—ntfacility AnnRPt_426-aon.aoc Page: 617 <br />