ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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1 ARCADIS Phase II Field Investigation and LNAPL ' Mobility Evaluation Report Union Pacific Railroad Company Former Maintenance Facility tTracy,California Historically, three monitoring wells (MW-6A, 8A, and 11A),five piezometers (PZ- 01, 02, 08, 09, and 10)and four temporary wells (TW-01, 02, 03, and 04) have contained measureable LNAPL. LNAPL thickness and water elevation are graphed against time on Figures 4, 5, and 6.A graph for PZ-08 was not included because ' LNAPL was observed only once in this well (November 2000). Maximum historical LNAPL thickness measured in November 2008 was 2.38 feet in ' well MW-6A. The LNAPL thickness observations demonstrate an inverse relationship to the corrected groundwater elevation (i.e., LNAPL thickness increases as groundwater levels decrease). This is common in unconfined aquifer systems as LNAPL is trapped beneath the water table and immobile during high-water conditions and drains under gravity during low-water conditions. t4.1.2 LIF Results LIF results are presented on Figure 7 as percent reference emitter fluorescence. Data ' from 31 locations suggest LNAPL extends from the Engine House to LIF-32 (located approximately 150 feet west of the Engine House)and from approximately 40 feet south of the oil-water separators(LIF-19 and LIF-20)to the railroad tracks. LNAPL impacts generally occur between 8 and 15 feet bgs,which is consistent with the historical water-table fluctuations. LIF data were not recorded at depths shallower than 5 feet bgs because the boring locations were hand augered to clear for underground utilities. Note,the observations of LNAPL noted in Figure 8 only represent observed ' LNAPL in wells and do not represent LIF results. As such, the LIF results do not correlate exactly with the observed LNAPL in wells (i.e. comparing Figures 7 and 8) primarily because the LIF results are interpretive(based on relative fluorescence)while ' the groundwater results are based on pure observation of LNAPL. LNAPL was observed at depths shallower than 7 feet bgs at locations LIF-02, LIF-03, ' LIF-04, and LIF-06. LNAPL impacts were observed at depths deeper than 15 feet bgs at LIF-02, LIF-05, and LIF-23. At LIF-02, LIF data indicated LNAPL at 5 feet bgs indicating this area may be a surface spill source. ' Elevated percent reference emitter fluorescence was observed at locations LIF-02, LIF-27, LIF-28, and LIF-29,which are located along subsurface utility trenches that run ' from the track pan to the oil-water separator suggesting that the underground utility potentially served as migration pathway for LNAPL. mwa�aey maai'.'M11.29=0)dm 12