Characterization of Vadose Zone Sediment: Borehole 41-09-39 in the S-SX Waste Management Area

Abstract

The overall goal of the of the Tank Farm Vadose Zone Project, led by CH2M HILL Hanford Group, Inc., is to define risks from past and future single-shell tank farm activities. To meet this goal, CH2M HILL Hanford Group, Inc., asked scientists from Pacific Northwest National Laboratory to perform detailed analyses on vadose zone sediment from within the S-SX Waste Management Area. This report is one in a series of four reports to present the results of these analyses. Specifically, this report contains all the geologic, geochemical, and selected physical characterization data collected on vadose zone sediment recovered from borehole 41-09-39 installed adjacent to tank SX-109. This report also presents our interpretation of the data in the context of the sediment lithologies, the vertical extent of contamination, the migration potential of the contaminants, and the correspondence of the contaminant distribution to groundwater. The information presented in this report supports the field investigation report prepared by CH2M HILL Hanford Group, Inc. (a) The geology under the SX Tank Farm forms the framework through which the contaminants move, and provides the basis with which to interpret and extrapolate the physical and geochemical properties that control the migration and distribution of contaminants. Of particular interest are the interrelationships between the coarser-and finer-grained facies and the degree of contrast in their physical and geochemical properties. The vertical distribution of cesium-137, based on borehole gamma logging and the laboratory analysis of the sediment at borehole 41-09-39, suggests that much of the tank fluid that leaked from tanks SX-108, and/or SX-109, traveled within the coarse-grained Hanford formation H1 unit that is found between 20.4 and 26.8 meters (67 and 88 feet) below ground surface (bgs) at borehole 41-09-39. It is difficult to differentiate natural zones of higher moisture content due to the presence of finergrained material (finer-grained material retains higher moisture contents) from zones of excess moisture resulting from leaked fluid. Thus, moisture content distribution did not give us a clear indication of the vertical extent of the plume. However, moisture content does help identify intervals that have been recently impacted by drilling operations. The pH values are not nearly as high as would be expected for tank liquor completely saturating sediment. Therefore, it would appear that significant pH reactions occur from the tank bottoms at ~16.8 meters (~55 feet) to a maximum of 27.4 meters (90 feet) bgs for sediment surrounding the tanks. The electrical conductivity results suggest that the tank leak fluid dominates the porewater down to a depth of 38.8 meters (127.4 feet) bgs and the deepest (leading edge of plume) is in borehole extension sleeve 3A, at a depth of 41.4 meters (136 feet). For other borehole extension sleeves below 41.4 meters (136 feet) bgs, the electrical conductivity does not show any significant deviations from values found for (a)

Characterization of Vadose Zone Sediment: Borehole 299-E33-46 Near B 110 in the B BX-BY Waste Management Area

“…If the absolute concentrations of co-migrating species are changed solely by dilution with existing porewater, then the ratio of the two should remain constant. Unlike similar ratio discussions for other contaminated boreholes (SX-41-09-39 and 299-W23-19; see Serne et al 2002b and2002d), the ratios for the porewaters from borehole 299-E33-46 are not constant. It is likely that the low absolute concentrations of constituents such as technetium-99 and relatively low concentrations of nitrate and uranium cause the ratio approach to be compromised by analytical error.…”

“…This differs from the cation profile from borehole 299-W23-19 that shows very distinct separation of the divalent cations from the sodium plume (see Figure 4.4 in Serne et al 2002b) or the less pronounced but still discernable separation from the sodium profile at the two more saline plumes between SX-108 and SX-109 tanks (see Figures 4.3 in both Serne et al 2002c and2002d). Based on personal communication with Dr. Carl Steefel at Lawrence Livermore National Laboratory, the ion exchange separation of the divalent cations, which are naturally the dominant cations on Hanford sediment exchange sites, from the invading high sodium fluids is maximized when the invading sodium concentrations are not large and when the ion exchange capacity of the sediments is moderate.…”

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

“…The sodium pushed the natural divalent cations off the sediment cation exchange sites in the sediments between 40 and 93 ft bgs. We have observed the same cation distribution and ion exchange fronts where divalent cations and sometimes potassium are depleted in the shallow sediments, and high levels of water-extractable sodium are present at both the SX and BX tank farms where tank fluids have been confirmed as being present (see Serne et al 2002bSerne et al , 2002c for details). At and right below the leading edge of the sodium plume, one finds elevated levels of the divalent cations that were displaced.…”

“…In contrast, based on the data from the TX background borehole (see Serne et al 2004 for details), the Cold Creek lower subunit (caliche) is very poorly sorted and has a wide range of particle sizes from gravel to silt and clay, as has been described previously for sediments below the SX tank farm (Serne et al 2002a(Serne et al , 2002b(Serne et al , 2002c(Serne et al , 2002d. The hydrometer results and wet sieving results are combined in Figures 4.10 and Figure 4.11 as plots of "cumulative percent finer than" versus "particle size in microns".…”

“…In the latter figures the actual porewater concentrations are also plotted to allow comparison between the derived porewaters and actual porewaters. As discussed in several other Vadose Zone Characterization Project reports, the dilution-corrected 1:1 sediment:water extracts are a reasonable estimate of the actual vadose zone porewater, especially when highly saline tank fluids are present (see Serne et al 2002bSerne et al , 2002c. 4.37…”