ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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Phase II Field ARC�dS Investigation and LNAPL Mobility Evaluation Report Union Pacific Railroad Company Former Maintenance Facility 1Tracy, California ■ Criteria 4—No water wells, deeper drinking water aquifers,surface water, or other sensitive receptors are likely to be impacted. ■ A survey of off-site wells within 2,000 feet of the Site was conducted in 1997 as described in the TPH Position Papersubmitted by Terranext on May 5, 1997(Terranext 1997). No wells identified in this survey were screened above 60 feet bgs. Groundwater impacts at this Site are restricted to the A- zone,which occurs between 10 and 25 feet bgs. B-and C-Zone wells screened below 25 feet bgs have concentrations below cleanup levels. ■ In addition, based on phone conversations with the City of Tracy as well as San Joaquin County, it is expected that wells identified are no longer used or used for agriculture and that residences near the Site get their water from the City of Tracy. The City of Tracy gets 7 percent of the water from groundwater and has eight wells all screened in the deeper confined aquifer from 300 to 400 feet bgs. The four wells closest to the Site are located northwest of the Site in the upgradient direction. • Criteria 5—The Site presents no significant risk to human health. ■ The Site is currently a rail yard used mostly for rail car hookup and light maintenance. The property is expected to remain commercial/industrial use as a rail yard in the future. Based on the current and anticipated future use of the Site, commercial/industrial workers, maintenance workers, and construction workers are the relevant current and future human receptors who may encounter site contaminants in soil or groundwater. ■ Commercial/industrial workers and maintenance workers may be exposed to soils at 0 to 2 feet bgs through direct contact exposure pathways (incidental soil ingestion, dermal contact, and airborne particulate inhalation)and construction workers may be exposed to soils to a depth of 10 feet bgs through the same direct contact exposure pathways. Therefore,these exposure pathways are considered complete exposure pathways. ' Ingestion of groundwater is an incomplete exposure pathway for all site workers because groundwater beneath the Site is not used as a drinking water source.With one exception, direct contact exposures associated with groundwater(dermal contact)are generally incomplete for all site workers ' because shallow groundwater occurs at depths (10 to 25 feet bgs) below which workers may reasonably be exposed to groundwater. The exception is the former TPCA Pond Excavation, which was not backfilled following excavation and therefore its elevation is currently about 10 feet lower than the rest of the Site.As such, groundwater is encountered within the former TPCA Pond Excavation just below ground surface; grab groundwater samples collected in November 2009 were collected from 1 to 5 feet below ' the current surface of the former TPCA Pond Excavation. Because the entire 1 rpt-upa4racyaaapImotkdyty91-2 2010)dm 30