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depth of approximately five (5) feet bgs. The drain consisted of a corrugated steel pipe, approximately 12 inches in diameter with holes placed in the bottom of the pipe, the holes positioned downward, and the trough filled with pea gravel to approximately two (2) feet bgs (Wallace Kuhl, 2005; Plate No. 3). This meets the description of a French drain as specified by the American Railway Engineering and Maintenance of Way Association (AREMA) (2003). 1.5 HYDROGEOLOGY Depth to groundwater beneath the Site is between 15 and 20 feet below ground surface (bgs), from north to south, along Lincoln Street, and is between 15 and 20 feet bgs across Parcel 3, based on depth-to-water data collected by Wallace Kuhl (2005) during borehole advancement. Groundwater may be confined to semi-confined beneath clay layers. Historic groundwater elevations for the Site and adjacent areas are provided in Table 1. Hydrographs of historic groundwater elevation data are presented in Figure 2a through Figure 2e. Groundwater elevation data for monitoring wells constructed with screens intersecting "first" groundwater have been summarized in Table 2. These data were used to generate a groundwater potentiometric surface contour map as shown on Figure 3. The groundwater elevation varies from approximately one (1) foot below mean sea level (imp along West Weber Avenue to greater than ten (10) feet below msl to the south of former Main Street. The groundwater surface (gradient) slopes to the south in the northern portion of the site, and probably bends to the southeast in the southern portion of the Site. "Review of the Spring of 1999 San Joaquin County Flood Control and Water Conservation District Lines of Equal Elevation of Groundwater Map reveals groundwater beneath the property at approximately 20 feet bgs and regional groundwater flow direction to be towards the southeast. Regional groundwater flow direction can be affected by stage fluctuation of the nearby Stockton Deep Water Channel, Mormon Slough, ground water pumping, time of year and other factors," (Wallace Kuhl, 2005). Monitored groundwater elevation changes during a 48-hour tidal influence survey in 1999 indicated tidal influence specific to groundwater flow direction change was not significant, yet specific tidal influence could not be defined based on the dataset l . The study stated that "it does not appear tidal variations within the channel are affecting the groundwater flow direction beneath the Stockton Group property," this property located to the immediate west of the Stockton UPRR Project area. During this period, tidal fluctuations in the Stockton Channel varied by as much as four (4) feet between high and low tides, yet groundwater changes varied less than 0.1 feet. 1.6 CONTAMINANT DISTRIBUTION 1.6.1 CONTAMINANT DISTRIBUTION IN SOIL Limited soil and groundwater sampling data are available for the areas identified as Parcel 24 and Parcel 3. Data are not available for Parcel 4. In Parcel 3, Treadwell & Rollo (2001) advanced nine (9) soil boreholes and collected four (4) Hydro punch groundwater samples. Prior to this investigation, four (4) test pits (Test Pits 3TP-1, 3TP-2, 3TP-3 and 3TP-4) were dug and two (2) soil boreholes (Boreholes 3B-1 and 3B-2) were advanced by Treadwell and Rollo (1999). I Environmental Resolutions, Inc., 1999, pg 3, June 1 1 th Golden State Environmental, Inc. - I - Los Angeles, San Diego and Houston Revised Work Plan — Soil and GW Characterization July 2006