Table 2.1. Stratigraphy of the Vadose Zone Beneath the SX Tank Farm. Stratigraphic Symbol (a) Formation Facies/Subunit Description Genesis Holocene/Fill NA Backfill Poorly sorted gravel to medium sands and silt derived from the Hanford formation (Price and Fecht, 1976a) Anthropogenic Unit H1a-gravelly sand Upper coarse-grained sequence equilvalent to Johnson et al.'s (1999) "Hanford Gravel Unit B" and Sobczyk's (2000) "Hanford Unit B" H1a Unit H1a-slightly silty sand Upper fine sand and silt sequence. Equivalent to "Hanford silty sand" of Sobcyzk (2000) H1 Unit H1 Lower coarse-grained sequence equivalent to "Gravel Unit A" described by Johnson et al. (1999) and "Hanford Unit A" described by Sobcyzk (2000).

Executive SummaryThis report was revised in September 2008 to remove acid-extractable sodium data from Tables 4.15 and 4.19. The sodium data was removed due to potential contamination introduced during the acid extraction process. The rest of the text remains unchanged from the original report issued in February 2002.The Tank Farm Vadose Zone Project is led by CH2M HILL Hanford Group, Inc. Their goals include defining risks from past and future single-shell tank farm activities, identifying and evaluating the efficacy of interim measures, and collecting geotechnical information and data. The purpose of these activities is to support future decisions made by the U.S. Department of Energy (DOE) regarding near-term operations, future waste retrieval, and final closure activities for the single-shell tank Waste Management Areas. To help in this effort, CH2M HILL Hanford Group, Inc. contracted with scientists at Pacific Northwest National Laboratory to analyze sediment samples collected from borehole 299-W23-19.Borehole 299-W23-19 was drilled at the southwestern edge of tank SX-115 as a characterization borehole to evaluate the depth distribution of contamination leaked from tank SX-115. The borehole was cored throughout the vadose zone during drilling. The geology, stratigraphy, and lithology of the drill core were described in the field and in the laboratory. The drill cores were sampled for analyses of physical, chemical, and hydraulic properties in order to better understand the distribution of contaminants and the mechanisms of contaminant movement beneath the SX tank farm.Electrical conductivity and chromium, nitrate, sodium, and technetium concentrations were found to be good indicators of the plume distribution. Data for the other measured contaminants indicate that leaked tank fluids have impacted the vadose zone beneath tank SX-115 from about 22.2 meters (73 feet) depth to the base of the upper Plio-Pleistocene unit at about a 47.5 meters (156 feet) depth. The technetium-99 plume, however, appears to occur as deep as 62.5 meters (205 feet), which is the depth of the deepest sample.The bulk of the leaked fluid beneath tank SX-115 resides in the upper Plio-Pleistocene unit between a 38.1 meters (125-feet) and 47.5 meters (156-foot) depth. This is slightly deeper than the contamination investigated at tank SX-108 and tank SX-109, both of which have the bulk of contamination in the shallower Hanford formation.Results of chemical analyses point to three potential mechanisms influencing the distribution of contaminants in the vadose zone. Common ion exchange reactions appear to have influenced the distribution of most mobile contaminants whereas oxidation-reduction reactions seem to have influenced chromium distribution. Observations from this study suggest that nitrate, technetium-99, and perhaps molybdenum migrate with no measurable retardation in the vadose zone whereas sodium, chromium, and selenium migrate with a small amount of retardation. These conclusions are similar to the conclusions found during the S...

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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)

This report was revised in September 2008 to remove acid-extractable sodium data from Tables 4. 8, 4.28,4.43, and 4.59. The sodium data was removed due to potential contamination introduced during the acid extraction process. The rest of the text remains unchanged from the original report issued in April 2004.The overall goal 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 at Hanford. To meet this goal, CH2M HILL Hanford Group, Inc. tasked scientists from Pacific Northwest National Laboratory to perform detailed analyses on vadose zone sediments from within Waste Management Area (WMA) T-TX-TY. This report is the first of two reports written 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 boreholes C3830, C3831, and C3832 in the TX Tank Farm, and from borehole 299-W-10-27 installed northeast of the TY Tank Farm.