Characterization of Vadose Zone Sediments Below the TX Tank Farm: Probe Holes C3830, C3831, C3832 and 299-W10-27
Pacific Northwest National Laboratory performed detailed analyses on vadose zone sediments from within Waste Management Area T-TX-TY. This report contains all the geologic, geochemical, and selected physical characterization data collected on vadose zone sediment recovered from three probe holes (C3830, C3831, and C3832) in the TX Tank Farm, and from borehole 299-W-10-27. Sediments from borehole 299-W-10-27 are considered to be uncontaminated sediments that can be compared with contaminated sediments. This report also presents our interpretation of the sediment lithologies, 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 TX Tank Farm. Sediment from the probe holes was analyzed for: moisture, radionuclide and carbon contents;, one-to-one water extracts (soil pH, electrical conductivity, cation, trace metal, and anion data), and 8 M nitric acid extracts. 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 did not observe significant indications of caustic alteration of the sediment mineralogy or porosity, or significant zones of slightly elevated pH values in the probe holes. The sediments do show that sodium-, nitrate-, and sulfate-dominated fluids are present. The fluids are more dilute than tank fluids observed below tanks at the SX and BX Tank Farms. Three primary stratigraphic units were encountered in each probe hole: (1) backfill material, (2) the Hanford formation, and (3) the Cold Creek unit. Each of the probe holes contain thin fine-grained layers in the Hanford H2 stratigraphic unit that may impact the flow of leaked fluids and effect irregular and horizontal flow. The probe holes could not penetrate below the enriched calcium carbonate strata of the Cold Creek lower subunit; therefore, we did not identify the maximum vertical penetration of the tank related plumes. However, the more elevated portions of the electrical conductivity (EC) profile at probe hole C3830 currently resides at the bottom of a fine-grained thin lens in the Hanford H2 unit at 87 ft bgs. At C3831, we lack good sample coverage to ascertain whether the salt plume has significantly descended into the Cold Creek Unit. There is strong indication at probe hole C3832 that the saline plume has descended into the Cold Creek Unit. The profiles do collectively suggest that the deepest penetration of tank related fluids is found in probe hole C3832. The water potential data from 299-W10-27?s H2 unit, the unit where most of the contaminants reside in the TX probe holes, are consistent with a draining profile. Despite the evidence that elevated EC values may be present in all three probe holes to their depth of refusal, the concentrations of long-term risk drivers are not large. The inventories of potential contaminants of concern, nitrate, technetium-99, uranium, and chromium, are provided. In addition, in situ desorption Kd values for these contaminants are provided. For conservative modeling purposes, we recommend using Kd values of 0 mL/g for nitrate and technetium-99, a value of 1 mL/g for uranium, and 10 mL/g for chromium to represent the entire vadose zone profile from the bottoms of the tanks to the water table. These conservative Kd values along with the provided inventories in the vadose zone sediments obtained from the three probe holes can be used in long-term risk projections that rely on estimates of water recharge and vadose zone and aquifer transport calculations.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 15020750
- Report Number(s):
- PNNL-14594; 1752; 2536; 830403000; TRN: US0504658
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
HANFORD RESERVATION
STORAGE FACILITIES
SITE CHARACTERIZATION
SOILS
SEDIMENTS
GEOCHEMISTRY
GEOLOGY
BOREHOLES
CONTAMINATION
environmental molecular sciences laboratory
Vadose Zone Characterization
TX Tank Farm
tank leaks
in-situ Kd values
geology