RCRA Groundwater Quality Assessment Report for Single-Shell Tank Waste Management Area TX-TY (January 1998 through December 2001)

Abstract

Waste Management Area (WMA) TX-TY at the Hanford Site contains the TX and TY single-shell tank farms and their auxiliary equipment. These tank farms, located in the northern portion of the 200 West Area, include 24 single-shell carbon steel tanks constructed in the 1940s and early 1950s. During operations, tanks received mixed waste from plants that processed spent reactor fuel to recover plutonium as part of Hanford's defense mission. The tank farms ceased active operations in 1980 but are currently storing waste and are currently regulated as Resource Conservation and Recovery Act (RCRA) Interim Status Facilities. Waste Management Area TX-TY was placed in RCRA Groundwater Quality Assessment in 1993 and has remained in that status because of indications that dangerous-waste contaminants from within the area may be entering groundwater. The water table is declining and groundwater flow directions are changing in the vicinity of WMA TX-TY. These changes are a result of the cessation of effluent discharge to ground in 1995 and the initiation of a major pump-and-treat operation in 1998. To meet the changing groundwater monitoring needs, twelve new RCRA monitoring wells have been constructed since 1997 and two others are in the planning stage. Monitoring at WMA TX-TY indicates that the dangerous-waste constituent chromium occurs above the drinking water maximum contaminant level at one well east of the WMA. Although the nearest potential source for the chromium is the WMA and the chromium is attributed to the WMA, the high concentrations of chromium appear to be deeper in the aquifer than the maximum concentrations of nonregulated technetium-99, which is most likely from WMA TX-TY. Chromium contamination is located on the downgradient (east) side of the WMA and is currently migrating to the southeast. The dangerous-waste constituent carbon tetrachloride is also present at WMA TX-TY. The carbon tetrachloride is from a well document, upgradient source associated with the Plutonium Finishing Plant. Data gathered during drilling indicates that the carbon tetrachloride is distributed relatively deep in the upper part of the aquifer at WMA TX-TY.