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ante ' roup Additional Site Investigation Work Plan UPRR Bunkers- Tracy 780 East 6th Street Tracy, California 1.0 INTRODUCTION AND PURPOSE Antea®Group has prepared this Additional Site Assessment Work Plan on behalf of Union Pacific Railroad Company(UPRR) in response to the letter from the Central Valley Regional Water Quality Control Board (RWQCB)dated July 14,2023(Appendix A).This proposed investigation is for the historic Tracy Station at 780 East 6th Street,Assessor's Parcel Number 235-15-002 in Tracy,California (further referred to as the"Site"). The RWQCB has identified this site in Geo Tracker under Global ID T10000021214.The purpose of the proposed scope of work is to evaluate risks to human health and environment associated with the former underground fuel storage and distribution systems previously identified at the Site and the possibility of abandoning the structures in place.The Site location is shown on Figure 1 and the estimated location of the former underground fuel storage structure is shown on Figure 2.Antea Group's Standard Operating Procedures(SOPS)are provided in Appendix B. 2.0 BACKGROUND From 2016 through 2019, UPRR proactively evaluated Southern Pacific historic rail yard operations in California, requesting Antea Group conduct research on these yards to identify potential locations of former underground fuel storage and distribution systems.Such systems became more common as the phaseout of coal energy began from the late 1920's to mid-1940's.Antea Group reviewed historical Southern Pacific documents looking for site maps or illustrations showing the location of former fuel storage or distribution structures and recent aerial imagery to examine the present-day condition of the area.Subsequently,a non-intrusive geophysical survey was performed at the Site to search for these features on April 13, 2016. A concrete sump was identified at the Site during the 2019 intrusive investigation completed on July 23, 2019. The size was not recorded.An estimated location is shown on Figure 2.At the suspected concrete sump,four grab soil samples were collected from outside the corners and one sediment sample was collected from the inside.Among the five samples collected, naphthalene was only detected in the inside sump sediment sample at a concentration above the Tier 1 Environmental Screening Level (ESL) (RWQCB 2019 (Rev. 2)).Arsenic and vanadium concentrations above the Tier 1 ESLs were detected in all the samples collected. In two of the outside sump samples, lead concentrations exceeded the Tier 1 ESL. In one of the samples with a lead exceedance and one other sample collected outside the sump,thallium concentrations exceeded the Tier 1 ESL. 3.0 PROPOSED FIELDWORK For this initial phase of investigation(Phase 1),Antea Group proposes to advance exploratory borings around the structure previously identified at the Site to further assess soil laterally outside and vertically beneath the structure(Figure 2).The proposed activities will be overseen by a licensed California Professional Geologist.The work will be conducted in compliance with State and local regulations and in general accordance with the Leaking Underground Fuel Tank Guidance Manual September 2012(Revised December 2015)from the California State Water Resources Control Board. �INOGEN� ALLIANCE uS_artteagrbup.Carn 1