Characterization of Vadose Zone Sediments Below the T Tank Farm: Boreholes C4104, C4105, 299-W10-196 and RCRA Borehole 299-W11-39

Serne, R JEFFREY. ; Bjornstad, Bruce N. ; Horton, Duane G. ; Lanigan, David C. ; Lindenmeier, Clark W. ; Lindberg, Michael J. ; Clayton, Ray E. ; LeGore, Virginia L. ; Geiszler, Keith N. ; Baum, Steven R. ; Valenta, Michelle M. ; Kutnyakov, Igor V. ; Vickerman, Tanya S. ; Orr, Robert D. ; Brown, Christopher F.

Pacific Northwest National Laboratory (U.S.)

关键词: Geochemistry;    Vadose Zone Sediments;    Tank Leak;    Groundwater Plume;    T Tank Farm;   

DOI  :  10.2172/15020756
RP-ID  :  PNNL-14849
RP-ID  :  AC05-76RL01830
RP-ID  :  15020756

美国|英语

来源: UNT Digital Library

【 摘 要 】

This report contains geologic, geochemical, and physical characterization data collected on sediment recovered from boreholes C4104 and C4105 in the T Tank Farm, and 299-W-11-39 installed northeast of the T Tank Farm. The measurements on sediments from borehole C4104 are compared to a nearby borehole 299-W10-196 placed through the plume from the 1973 T-106 tank leak. This report also presents the data in the context of sediment types, the vertical extent of contamination, the migration potential of the contaminants, and the likely source of the contamination in the vadose zone and groundwater below the T Tank Farm. Sediment samples were characterized for: moisture content, gamma-emission radionuclides, one-to-one water extracts (which provide soil pH, electrical conductivity, cation, trace metal, radionuclide and anion data), total carbon and inorganic carbon content, and 8 M nitric acid extracts (which provide a measure of the total leachable sediment content of contaminants). Overall, our analyses showed that common ion exchange is a key mechanism that influences the distribution of contaminants within that portion of the vadose zone affected by tank liquor. We observed slight elevated pH values in samples from borehole C4104. The sediments from the three boreholes, C4104, C4105, and 299-W10-196 do show that sodium-, nitrate-, and sulfate-dominated fluids are present below tank T-106 and have formed a salt plume. The fluids are more dilute than tank fluids observed below tanks at the SX and BX Tank Farms and slightly less than those from the most saline porewater found in contaminated TX tank farm sediments. The boreholes could not penetrate below the gravel-rich strata of the Ringold Formation Wooded Island member (Rwi) (refusal was met at about 130 ft bgs); therefore, we could not identify the maximum vertical penetration of the tank related plumes. The moisture content, pH, electrical conductivity, nitrate, and technetium-99 profiles versus depth in the three contaminated boreholes around T-106 do not clearly identify the leading edge of the plume. However, the profiles do collectively suggest that bulk of tank-related fluids (center of mass) still resides in Ringold Formation Taylor Flats member fine-grained sediments. Most of the chemical data, especially the nitrate and technetium-99 distributions with depth, support a flow conceptual model that suggests vertical percolation through the Hanford formation H2 unit near T-106 and then a strong horizontal spreading within the CCUu unit followed by more slow vertical percolation, perhaps via diffusion, into the deeper strata. Slow flushing by enhanced recharge and rapid snow melt events (Feb. 1979) appear to lead to more horizontal movement of the tank fluids downgradient towards C4105. The inventories as a function of depth of potential contaminants of concern, nitrate, technetium, uranium, and chromium, are provided. In-situ Kd values were calculated from water and acid extract measurements. For conservative modeling purposes we recommend using Kd values of 0 mL/g for nitrate, Co-60, and technetium-99, a value of 0.1 mL/g for uranium near borehole C4104 and 10 mL/g for U near borehole C4105, and 1 mL/g for chromium to represent the entire vadose zone profile from the bottoms of the tanks to the water table. A technetium-99 groundwater plume exists northeast and east of T WMA. The highest technetium-99 concentration in fiscal year 2003 was 9,200 pCi/L in well 299-W11-39. The most probable source for the technetium-99 is the T waste management area. Groundwater from wells in the west (upgradient) and north of WMA T appear to be highly influenced by wastes disposed to the cribs and trenches on the west side of the WMA. Groundwater from wells at the northeast corner and the east side of the WMA appears to be evolving towards tank waste that has leaked from T-101 or T-106.