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 SummaryAdditional data needed for development of a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) Phase III Feasibility Study to address a persistent uranium plume in 300 Area groundwater provided the stimulus for the limited field investigation (LFI) described in this report. The focus of the LFI was to determine the location and geochemical nature of the source for the uranium plume. These objectives were accomplished by drilling four new groundwater monitoring wells in the 300-FF-5 Operable Unit (OU) in fiscal year 2006 as defined in the Operable Unit Limited Field Investigation Plan (DOE 2006a). Wells 399-3-18 (C4999), 399-3-19 (C5001), 399-3-20 (C5002), and 399-1-23 (C5000) were drilled to characterize the uranium distribution in sediments in the vadose zone and the unconfined aquifer. In addition to uranium, the presence of other contaminants of concern were also evaluated.Uranium contamination in groundwater beneath the Hanford Site's 300 Area has persisted longer than predicted by modeling that was conducted during the 1990s as part of the initial remedial investigation for the 300-FF-5 Operable Unit. Even though discharge of uranium-bearing effluent to infiltration ponds and trenches ended by the mid-1980s, and removal of contaminated soil from former waste sites was accomplished in the late 1990s, the groundwater plume today continues to occupy a relatively constant area, with concentrations remaining within a fairly fixed range. Because portions of the plume exceed the drinking water standard for uranium (30 µg/L), the U.S. Department of Energy is supporting renewed remedial investigation activities and remedial action feasibility studies. The goal of this renewed effort is to find a remedy that will reduce uranium concentrations in the aquifer such that the aquifer is restored to its maximum beneficial use, i.e., as a potential supplier of drinking water.To provide the information necessary to proceed with the remedial action feasibility study and possible field treatability tests, a limited field investigation (LFI) has been conducted. The focus of the LFI was to determine the location and mobility characteristics for contaminant uranium that continues to re-supply the groundwater plume. Presumed sources include uranium remaining in the vadose zone and/or sequestered in the aquifer sediments, which interact with the fluctuating groundwater-river water. This information is fundamental for evaluating remedial action alternatives to reduce the concentration of uranium in groundwater to meet regulatory standards. New results provided by the LFI will be used in developing computer simulations of groundwater flow and uranium transport, in designing treatability field tests, and when implementing remedial action decisions.The four LFI borehole locations were chosen to represent various combinations of proximity to former waste disposal sites, proximity to the Columbia River, and wide ranging hydrogeologic features. Highly detailed descriptions of geologic features ...

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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Table 3.1. Drilling, sampling, geophysical logging, and well construction information for IFRC wells Well Name Well ID Function Samples Drilling Order Start Drilling End Drilling Geophysical Logging Total Depth (ft) Length Screen (ft) Top Screen Depth (ft) Bottom Screen Depth (ft) Bottom End Cap (ft) Instrument Depth (ft) % Recovery Hanford/Ringold Contact Depth (ft)