Executive Summary The overall goals of the Tank Farm Vadose Zone Project, led by CH2M HILL Hanford Group, Inc., are: 1) to define risks from past and future single-shell tank farm activities, 2) to identify and evaluate the efficacy of interim measures, and 3) to aid, via collection of geochemical information and data, the future decisions that must be made by the U.S. Department of Energy (DOE) regarding the near-term operations, future waste retrieval, and final closure activities for the

more »

... le-shell tank Waste Management Areas (WMAs). For a more complete discussion of the goals of the Tank Farm Vadose Zone Project, see the overall work plan, Phase 1 RCRA Facility Investigation/Corrective Measures Study Work Plan for the Single-Shell Tank Waste Management Areas (DOE 1999). Specific details on the rationale for activities performed at WMAs T and TX-TY are found in Crumpler (2002) . To meet these goals, CH2M HILL Hanford Group, Inc., asked scientists from Pacific Northwest National Laboratory (PNNL) to perform detailed analyses of vadose zone sediment collected within the T and TY Tank Farms. Specifically, this report contains all the geologic, geochemical, and selected physicochemical characterization data compiled on vadose zone sediment recovered from direct push samples collected near tanks 241-TY-105 and 241-TY-106 in the TY single-shell tank farm and near tanks 241-T-101 and 241-T-104 in the T single-shell tank farm. Additionally, this report compiles data from direct push samples collected north of the T Tank Farm in support of interim measures. A geochemical investigation in the vicinity of tanks 241-TY-105 and 241-TY-106 was performed using pairs of direct push probe holes. A total of 31 direct pushes were driven within the TY Tank Farm; 25 of these holes were logged for moisture, gross gamma, and spectral gamma using calibrated probes and six were driven for the purpose of retrieving vadose zone sediment for characterization and analysis. The samples were collected around tank 241-TY-105, which was estimated to have leaked 35,000 gal of tributyl phosphate (TBP) waste (UPR-200-W-152) from the uranium recovery process to the vadose zone in 1960 (Wood et al. 2001) , and tank 241-TY-106, which was estimated to have leaked 20,000 gal of TBP-uranium recovery waste to the vadose zone in 1959 (UPR-W-153). Additionally, this report contains all the geochemical and selected physical characterization data collected on vadose zone sediment recovered from seven direct push characterization holes emplaced to investigate vadose zone contamination associated with an leak from tank 241-T-101. Deaton (DOE 1992) postulated that a leak from tank 241-T-101 resulted in a loss of 28,390 liters (7,500 gallons) of tank waste to the subsurface. This event was the basis for placing tank 241-T-101 on the list of assumed/known leakers. It has been estimated that 1230 Ci of cesium-137, 0.0434 Ci of cobalt-60, and 0.382 Ci of technetium-99 were lost to the vadose zone as a result of the 1992 leak event (Wood et al. 2001) . A total of 19 probe holes were emplaced around tanks 241-T-101 and 241-T-104. Fourteen of these holes were logged for moisture, gross gamma, and spectral gamma using calibrated probes. A zone or depth of interest was identified for sampling in each probe hole based on neutron moisture logging data. Once an appropriate sampling depth was identified, a second hole was pushed as close as possible to the logged hole for collection of 1.5 feet of core material at the depth of interest. Due to lack of contaminants found during logging, field limitations, and poor sample recoveries, only five holes were successfully driven for the purpose of collecting vadose zone sediment samples.