ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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ARCADIS Phase II Field ' Investigation and LNAPL Mobility Evaluation Report Union Pacific Railroad Company Former Maintenance Facility Tracy, California In October 1992, 315 linear feet of fiberglass track pan were installed under existing track, in front of the Station House, and a new storm-water collection system was installed. The ASTs were converted into oil-water separators as part of the new storm-water collection system. Oily drippings and storm water from locomotives were ' collected in the pans, drained to a sump, and then pumped to the oil-water separator system. This system is no longer active. Current operations and the anticipated future operations at the Site are primarily related to railcar storage and hookup. Some light maintenance and cleaning occurs within the track pan areas.According to UPRR incident reports, a few minor(fewer than 50 gallons) releases have occurred at the track pan during the past 10 years. These minor releases were mitigated by UPRR contractors at the time of release. Refueling currently is performed at alternate off-site locations. 1.2.2 Remedial Actions Historical remedial activities at the Site include excavating contaminated soil from the TPCA pond; extracting,treating, and reinjecting groundwater; operating a soil-vapor extraction system, operating a dual-phase extraction system; and removing free-phase product(diesel fuel)from individual wells. ' Diesel product removal (including product skimmers, bailing, bilge bags, and hydrophobic absorbent socks)was conducted from 1989 to November 2007 at wells t MW-06A, MW-11A, PZ-01, PZ-02, PZ-08, PZ-09, PZ-10, TW-01, TW-02,TW-03, and TW-04. Approximately 650 pounds of product were removed from the subsurface between 1995 and 2006 (Environmental Resources Management[ERM]2006). ' Approximately half of the product removed was removed using the dual-phase extraction system. During operation of the dual-phase extraction system in the source area and installation of absorbent socks in product-affected wells, the thickness of free product detected in monitoring wells and piezometers declined. As described in the Remedial Investigation [RI] Report submitted by Industrial 1 Compliance[IC]on May 2, 1994(IC 1994), diesel product was first observed in MW- 06A shortly after it was installed in 1989. Initially, diesel product was bailed from MW- 06A monthly because UPRR tested free-product yield and found it to be too low to t support using a product pump. During the May 1992 sampling event, approximately 1.4 feet of product was measured in MW-6A(IC 1994). This marked a large increase over the average product thickness(0.8 feet) previously measured in the well.The increase was attributed to the installation of a dedicated groundwater sampling pump. The pump was removed later that year. In August 1992, a product skimmer pump was installed in 0-uP94a 4napl moeolml 1-29-2010)dm 4