ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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ARCADIS Phase II Field Investigation and LNAPL t Mobility Evaluation Report Union Pacific Railroad Company ' Former Maintenance Facility Tracy, California refueling facility for locomotive operations. Light maintenance activities were performed in the Engine House,while diesel and locomotive refueling activities were conducted in an area southwest of the Engine House (Figure 2). ' Groundwater monitoring has been conducted at the Site under the oversight of the RWQCB since 1995. The present groundwater monitoring program is performed semiannually to satisfy the requirements of RWQCB Monitoring and Reporting Program (MRP)No. R5-2002-0807. Site constituents of concern (COCs) have included TEPH as diesel(TEPH-d)and volatile organic compounds (VOCs). VOCs are rarely detected in groundwater samples collected from site monitoring wells and have not ' been detected above cleanup goals since 2006. Groundwater data collected during the last five years indicate that groundwater is affected by dissolved-phase TEPH. Dissolved-phase TEPH extends from the TPCA pond approximately 900 feet downgradient. Historically,free-phase product has been observed in 12 wells at the ' Site(MW-6A, MW-08A, MW-11A, PZ-01, PZ-02, PZ-08, PZ-09, PZ-10, TW-01,TW-02, TW-03, and TW-04). ' The focus of site investigation activities was assessing the presence and distribution of dissolved-phase TEPH and residual LNAPL. Potential sources of LNAPL and previous LNAPL remediation are outlined in the following text. Groundwater monitoring results ' from November 2002 through June 2010 are presented in Table 1. 1.2.1 Potential Sources ' Possible contaminant sources at the Site include potential releases during locomotive diesel fueling activities in the vicinity of two former 12,000-gallon aboveground storage ' tanks (ASTs) later converted to oil-water separators, past maintenance activities in the Engine House, and structures formerly associated with the collection, conveyance, and treatment of hydrocarbon waste streams. During the early 1960s through the late ' 1980s, storm-water runoff and hydrocarbon wastewater were collected in a series of sumps and piped to three unlined surface impoundments (the TPCA pond). In the first impoundment, a belt skimmer was used to recover waste oil into a 1,000-gallon oil ' recovery tank. The recovered oil was transported off site and recycled at a disposal facility. Water separated in the first impoundment was allowed to discharge to the other two impoundments and then into the Tracy municipal sanitary sewer system. On-site locomotive maintenance operations ceased in 1987 and refueling was significantly reduced. Remnants of the storm-water collection system sumps are still present at the Site,and their integrity was checked during Phase If field activities. Former sumps have been filled with concrete and appear in good condition, free of staining and water. Wp PuLary4nsPl maJi lua2mo).da. 3 t