Characterization of Vadose Zone Sediments from C Waste Management Area: Investigation of the C-152 Transfer Line Leak

A geologic/geochemical investigation in the vicinity of UPR-200-E-82 was performed using pairs of cone-penetrometer probe holes. A total of 41 direct-push cone-penetrometer borings (19 pairs to investigate different high moisture zones in the same sampling location and 3 individual) were advanced to characterize vadose zone moisture and the distribution of contaminants. A total of twenty sample sets, containing up to two split-spoon liners and one grab sample, were delivered to the laboratory for characterization and analysis. The samples were collected around the documented location of the C-152 pipeline leak, and created an approximately 120-ft diameter circle around the waste site. UPR-200-E-82 was a loss of approximately 2,600 gallons of Cs-137 Recovery Process feed solution containing an estimated 11,300 Ci of cesium-137 and 5 Ci of technetium-99. Several key parameters that are used to identify subsurface contamination were measured, including: water extract pH, electrical conductivity, nitrate, technetium-99, sodium, and uranium concentrations and technetium-99 and uranium concentrations in acid extracts. All of the parameters, with the exception of electrical conductivity, were elevated in at least some of the samples analyzed as part of this study. Specifically, soil pH was elevated (from 8.69 to 9.99) in five samples collected northeast and southwest of the C-152 pipeline leak. Similarly, samples collected from these same cone-pentrometer holes contained significantly more water-extractable sodium (more than 50 g/g of dry sediment), uranium (as much as 7.66E-01 g/g of dry sediment), nitrate (up to 30 g/g of dry sediment), and technetium-99 (up to 3.34 pCi/g of dry sediment). Most of the samples containing elevated concentrations of water-extractable sodium also had decreased levels of water extractable calcium and or magnesium, indicating that tank-related fluids that were high in sodium did seep into the vadose zone near these probe holes. Several of the samples containing high concentrations of water-leachable uranium also contained high pore water corrected alkalinity (3.26E+03 mg/L as CaCO3), indicating that the elevated water-leachable uranium could be an artifact of uranyl-carbonate complexation of naturally occurring labile uranium. However, a mass scan of the water extract containing the highest concentration of uranium was performed via inductively coupled mass spectrometry over the range of 230 to 240 atomic mass units, and a discernable peak was observed at mass 236. Although the data is considered qualitative, the presence of uranium-236 in the 1:1 sediment:water extract is a clear indication that the sample contains contaminant uranium [Hanford reprocessed fuel waste]. After evaluating all the characterization and analytical data, there is no question that the vadose zone surrounding the C-152 pipeline leak site has been contaminated by waste generally sent to tanks. The two zones or regions that contained the largest amount of contaminants, either in concentration or by occurrence of several key constituents/contaminants of concern, were located: 1) between the 241-C-151 and 241-C-152 Diversion Boxes (near the location of UPR-200-E-82) and 2) directly across the C-152 waste site near the C-153 Diversion Box (near where a pipeline, which connects the two diversion boxes, is shown on old blue prints . Without the use of more sophisticated analytical techniques, such as isotope signature analysis of ruthenium fission product isotopes, it is impossible to determine if the contamination observed at these two locations are from the same waste source or are a result of different leak events