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1 <br /> ARCADIS Phase II Field <br /> Investigation and LNAPL <br /> Mobility Evaluation Report <br /> Union Pacific Railroad Company <br /> ' Former Maintenance Facility <br /> Tracy,California <br /> based on historical monitoring well data as shown on hydrographs included on <br /> 1 Figures 4, 5, and 6 and in Appendix B. <br /> Hydraulic conductivity values were derived from site-specific constant-drawdown <br /> ' <br /> aquifer tests performed in 1993 by IC. Two of the monitoring wells, MW-7A and MW- <br /> 8A, in the 1993 testing were located near the delineated LNAPL area and represented <br /> the subsurface interval with impacted LNAPL. Slug test data were analyzed to <br /> ' determine transmissivity and storativity values using the Bouwer and Rice solution in <br /> the AQTESOL\im software. Slug test data collection and analysis is summarized in <br /> greater detail in the RI Report prepared by IC and dated May 2, 1994(IC 1994). <br /> ' Calculated transmissivity ranged from 170 to 210 square feet per day for MW-7A and <br /> MW-8A. Ten-foot well screens translate these transmissivity values to hydraulic <br /> conductivities of 17 to 21 feet per day. <br /> ' Fifty-three monitoring wells,temporary piezometers, and reinjection wells are regularly <br /> gauged for water levels at the Site. Hydraulic gradient is derived using water levels in <br /> ' on-site monitoring wells and implementing a calculation defined by Darcy's Slope and <br /> is presented in Equation 1: <br /> ' dh <br /> t — dl (Equation 1) <br /> Where, <br /> ' i = hydraulic gradient,dimensionless <br /> dh = difference between two hydraulic heads, feet <br /> dl = distance between the two wells,feet <br /> ' Hydraulic gradients calculated for the A-Zone ranged from 0.002 to 0.003,with an <br /> average of 0.0025(rounded to 0.003).A potentiometric surface map generated using <br /> data collected in March 2010 was used to estimate local hydraulic gradient values for <br /> the purposes of this evaluation. <br /> ' 3. Summary of Phase II Field Activities <br /> In accordance with the Work Plan (ARCADIS 2009a),ARCADIS conducted the Phase <br /> ' II field investigation including a combination of LIF and CPT/HP boring activities and <br /> saturated soil core collection. Investigations completed are described in the following <br /> sections. Field activities were conducted in accordance with a site-specific Health and <br /> t <br /> Mio�eacra„wmoaxNsszoiolem 6 <br />