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Union Pacific Railroad Company - 5 - 14 July 2023 <br /> Former Bunker C Vaults <br /> the risks associated with the release from the tank. Additionally, if the UST still contains <br /> liquid, then the contents of the tank must be removed and properly disposed. <br /> Silverthorn Site (GeoTracker ID: T10000021211) <br /> One underground structure was identified at the Silverthorn site during the initial <br /> investigation. Antea Group collected four soil samples from around the perimeter of the <br /> structure (not beneath) at depths of about 4 to 4.5 feet bgs. Antea Group was also able <br /> to access a port on the top of the structure and collect a liquid sample from within. The <br /> soil and liquid samples contained low petroleum concentrations. While Antea Group <br /> identified the liquid within the structure as petroleum fuel, they did not specify whether <br /> the contents of the structure were removed during the investigation. Antea Group did <br /> not remove the structure nor recommend further action for this site. Central Valley <br /> Water Board staff does not concur that no further action is necessary for this site. <br /> Though petroleum concentrations were not detected above ESLs in the soil analysis, <br /> Antea Group did not analyze for BTEX compounds in accordance with the LUFT <br /> manual and did not report whether the soil samples were collected from beneath the <br /> base of the structure. Antea Group also did not analyze a groundwater sample on site. <br /> These analyses are needed to complete a conceptual site model and assess risks to <br /> human health and safety and to the environment. The fuel within the abandoned tank <br /> must also be removed and properly disposed to prevent future discharges to the <br /> environment. <br /> Tracy Site (GeoTracker ID: T10000021216) <br /> At the Tracy site, Antea Group located a demolished subsurface structure during the <br /> initial site investigation. Antea Group collected four soil samples from depths of four to <br /> five feet bgs around the outside of the demolished structure. Antea Group also collected <br /> one sediment sample from within the underground debris area. Analysis of the soil <br /> sample from the center of the debris area detected 70 pg/kg of naphthalene, which <br /> exceeds the ESL for leaching to groundwater as a drinking water source. Antea Group <br /> recommended no further action for the Tracy site. Central Valley Water Board staff does <br /> not concur with Antea Group's recommendation. An analysis of soil samples from <br /> beneath the bottom of the demolished structure for petroleum compounds including <br /> BTEX is needed to determine if there has been a significant release from this area. An <br /> analysis of potential groundwater impacts is also needed to evaluate if there is a risk to <br /> human health or to the environment from potential releases from this underground <br /> structure. <br /> Willows Site (GeoTracker ID: T10000021216) <br /> Antea Group stated that it did not conduct an initial investigation of the Willows site <br /> because the property was not accessible during the previous site visit. Though Union <br /> Pacific no longer owns the property, Union Pacific is still considered responsible, along <br /> with the current property owner, for investigating potential impacts to groundwater and <br /> the environment from any existing subsurface tanks or structures. Central Valley Water <br /> Board staff recommends that Union Pacific coordinate with the current property owner <br /> to gain access to the site and submit a site investigation work plan to evaluate soil and <br />