ARCHIVED REPORTS PHASE II FIELD INVESTIGATION AND LNAPL MOBILITY EVALUATION REPORT

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' Phase II Field ARCADIS Investigation and LNAPL ' Mobility Evaluation Report Union Pacific Railroad Company Former Maintenance Facility ' Tracy, California TEPH-d in Monitoring Well Samples The highest TEPH-d concentration in monitoring well samples collected during March 2010 was detected in the sample collected from TW-03(2,100 pg/1), located north of ' the Engine House. High concentrations(above 1,000 pg/1)were also detected in samples collected from MW-02A and MW-07A suggesting that the former TPCA pond is a potential source of TEPH-d in groundwater. ' VOCs in Grab Groundwater and Monitoring Well Samples VOCs were detected in grab groundwater samples collected at HP-11, HP-18, HP-19, ' and HP-23. The highest VOC concentration detected was 53 pg/I (1,2,3- trimethylbenzene)at HP-11, where the highest TEPH-d concentrations were also detected. Concentrations were detected below cleanup levels at HP-18, HP-19,and ' HP-23. VOCs were also not detected above cleanup levels in March 2010 groundwater monitoring well samples.VOC analytical results for March 2010 groundwater monitoring were presented in the 2009/2010 Annual Monitoring Report, prepared by ' ARCADIS and dated April 27, 2010 (ARCADIS 2010b). These results confirm that VOCs have been remediated and are no longer a concern at the Site. ' 4.2.2 Dissolved-Phase Plume Stability The Air Force Center for Engineering and the Environment(formerly the Air Force ' Center for Environmental Excellence)created the program Monitoring and Remediation Optimization System(MAROS; GSI Environmental 2002),which includes tools for non-parametric statistical concentration trend analyses using the Mann- Kendall statistical test. Groundwater samples with concentrations of TEPH-d were analyzed in MAROS to evaluate the stability of the groundwater plume. Sampling results from 19 sampling events between February 2000 and March 2010 at seven t wells(MW-02A, MW-07A, MW-09A, MW-10A, MW-14A, MW-22A, and TW-03)were included in the Mann-Kendall analysis. Data prior to 2000 were not included in the analysis because detection limits were variable and higher and therefore most of the results were below detection limits. Results were removed from the data set if 1) TEPH-d was detected during fewer than six sampling events and 2) if free product was detected in the well during the last sampling event.These results were removed because MAROS could not accurately predict groundwater trends if they were used. The MAROS files are included in Appendix F. MLW +nwi mobil14t zo+o)aoc 16