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1 <br /> ' ARCADIS 2009/2010 Annual <br /> Monitoring Report <br /> Union Pacific Railroad <br /> Company <br /> Former Maintenance Facility <br /> • VOC concentrations in groundwater samples collected from the groundwater Tracy, California <br /> monitoring wells remain low and stable. In general,VOCs were not detected above <br /> ' laboratory reporting limits in the groundwater samples collected in March 2010, <br /> with the exception of one A-zone well (MW-27A) and B-zone well (MW-16B) where <br /> VOCs were detected below the CAO cleanup level. <br /> ' • The dissolved-phase TEPH-d plume in the A-Zone is laterally well defined and <br /> remains local to the source area (Figure 8). <br /> ' • Free-phase product continues to be observed in monitoring wells located near the <br /> source area, with measurable thicknesses ranging up to 23 inches. <br /> ' Based on these conclusions,ARCADIS recommends and is planning the following: <br /> ' • Preparing the Phase II Liquid Hydrocarbon investigation results (as outlined in the <br /> Phase 11 Liquid Hydrocarbon Work Plan submitted on January 6, 2009). <br /> • Continuing groundwater monitoring and sampling on a quarterly and/or semi- <br /> annual basis in accordance with the MRP to further evaluate the progress of <br /> natural attenuation of residual TEPH-d and VOCs in groundwater beneath the site. <br /> • Preparing an evaluation of the groundwater monitoring well network for <br /> abandoning and/or repairing wells as appropriate <br /> • Evaluating and submitting comments regarding the Draft Monitoring and Reporting <br /> Order prepared by the RWQCB and dated February 11, 2009 <br /> ' 9.0 References <br /> ARCADIS. 2009a. Phase II Investigation Work Plan.January 6. <br /> 2010.Well Installation Summary Report. March 11. <br /> Environmental Resources Management. 2003. Final Rebound and Remediation <br /> Effectiveness Evaluation.April 16. <br /> 2006.Additional Product Removal Proposal.August 28. <br /> PYWCAGISDAVIMWs tive\Unb Paac Tm YeMOeMar "GW M1lontlaroWj0 Tre Yam Mn,eIGW 20p}211R,FINFL2➢032010Pmd <br /> ' P.'d.� Page:7/7 <br />