Revised Geostatistical Analysis of the Inventory of Carbon Tetrachloride in the Unconfined Aquifer in the 200 West Area of the Hanford Site

Murray, Christopher J L; Bott, Yi-Ju

doi:10.2172/945229

Cited by 6 publications

(7 citation statements)

References 15 publications

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“…Simulations indicate that some DNAPL at the smaller footprint site may have reached the water table while at adjacent sites with larger footprints, the discharges are still in the vadose zone. Carbon tetrachloride fluxes related to these simulations are consistent with estimates of dissolved CT in the groundwater (Murray et al, 2006). Although the simulations, conditioned on laboratory evidence, show that the majority of the DNAPL emanating from the sources remains below the footprint of the disposal sites, the CT vapors can move rapidly in the lateral and vertical directions.…”

Section: Transport Of Organic Liquidssupporting

confidence: 78%

Hanford Site Vadose Zone Studies: An Overview

Gee

Oostrom

Freshley

et al. 2007

Vadose Zone Journal

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Large quantities of radioactive and chemical wastes resulting from Pu production for nuclear weapons are located in the vadose zone at the USDOE's Hanford Site, north of Richland, WA. The vadose zone here is characterized by often highly stratified glacial‐fluvial sediments that give rise to complex subsurface‐flow paths that contribute to uncertainty of contaminant fate and transport. Research efforts have focused on answering questions of contaminant transport from the viewpoint of geologic, biologic, geochemical, and hydrologic controls. This special section highlights key research topics concerning vadose zone problems at the Hanford Site. Research indicates that some of the contaminant species (137Cs, 60Co, 90Sr) are retained by Hanford sediments as a result of geochemical reactions, rendering them effectively immobile except under extremely saline or acidic conditions, while other species (99Tc, 129I, 3H) are typically mobile and have moved deep into the vadose zone and subsequently into groundwater. In addition, large quantities of organics, including carbon tetrachloride, have moved in complex ways as both vapor and liquid in the subsurface. Observed transport of mobile species is linked to liquid discharges and to elevated recharge rates that occur primarily at waste sites where land surfaces are void of vegetation and where winter rains have subsequently penetrated the subsurface wastes. A series of papers in this issue documents progress to date in understanding transport rates at Hanford, why anisotropy strongly affects the distribution of subsurface contaminants, why organic contaminants are difficult to find in the deep vadose zone, and what the impacts of hypersaline fluids are on waste form degradation and subsequent transport.

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Section: Transport Of Organic Liquidssupporting

confidence: 78%

Hanford Site Vadose Zone Studies: An Overview

Gee

Oostrom

Freshley

et al. 2007

Vadose Zone Journal

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“…The average CT mass of dissolved CT that has been transported across the water table (a measure of the impact of vapor phase transport to the groundwater table and pore water from the vadose zone entering the groundwater) for all three sites through 1993 is approximately 5,000 -10,000 kg. The accumulated CT mass in the aquifer would be significantly lower than the mass of CT in the groundwater estimated by Murray et al (2006) if only aqueous and vapor phase CT and no DNAPL phase entered the groundwater. This assessment indicated that it is likely that DNAPL CT has entered the groundwater.…”

Section: 4mentioning

confidence: 76%

“…Model results were also compared to this field data to evaluate reasonable scenarios for how CT entered the groundwater. For instance, with 100,000 kg of CT that entered the aquifer (based on the estimate in Murray et al 2006), only by combining the estimates of CT mass flux to the groundwater from simulation sensitivities (not the base cases) that show DNAPL crossing the water table predict a combined mass of CT (216-Z-9, Z-18, and Z-1A) in the aquifer similar to the estimated CT mass. The average CT mass of dissolved CT that has been transported across the water table (a measure of the impact of vapor phase transport to the groundwater table and pore water from the vadose zone entering the groundwater) for all three sites through 1993 is approximately 5,000 -10,000 kg.…”

Section: 4mentioning

confidence: 99%

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Oostrom¹,

Thorne²,

Zhang³

et al. 2008

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Three-dimensional simulations considered migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co-disposed organics in the subsurface beneath the two disposal sites as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Water-Oil-Air mode of Subsurface Transport Over Multiple Phases (STOMP) simulator.A large-scale model was configured to model CT and wastewater discharge from the major CT and waste-water disposal sites. A base-case simulation was conducted using hydraulic property values used in the base simulations reported in Oostrom et al. (2004;2006a;2006b) for local-scale simulations of the individual CT waste sites. Wastewater disposal resulted in increased water saturations in the Cold Creek Unit and a water table increase throughout the computational domain. The increased water saturations in the Cold Creek Unit reduced the downward movement of DNAPL CT and gaseous CT. Two sensitivity simulations were also performed using reduced permeability values and increased nonwetting-fluid entry pressure values for the Cold Creek Unit. The simulations conducted with smaller Cold Creek Unit permeability values than for the base case resulted in reduced DNAPL CT movement across the water table. For each case, additional simulations were conducted from 1993 to 2007 considering soil vapor extraction (SVE) from the well system in the vicinity of the three CT disposal sites. Partly due to the assumption of equilibrium partitioning between the various phase, considerably more CT was removed in the simulations compared to field observations. In addition to the large-scale simulations, a series of seven local-scale multifluid flow and transport simulations have been completed to quantify DNAPL, aqueous, and gas CT transport in the subsurface of the 216-Z-9 disposal site. This site was chosen for these simulations because, of the three major DNAPL disposal sites, it received the most DNAPL and it has the smallest footprint. For those reasons, previous simulations have shown that DNAPL disposed at this site would be able to penetrate deep into the subsurface 2006a), potentially to below the water table. In addition, CT concentrations of approximately 350,000 µg/kg were reported in a 1-ft thick lens, located at 19.8 m (65 ft) below the ground surface DOE-RL (2006). Six of the seven simulations (imposed cases 1-6) were conducted with imposed CT quantities in the Cold Creek Unit and/or the 1-ft thick silt lens, located in the Hanford 2 unit below the disposal site. The simulation period for these six cases was from 2007 -2107. The seventh case (modeled case) simulated flow and transport following aqueous phase and DNAPL disposal at the site using inventory data and SVE of 53,000 kg after 1993. The simulation period for this case was from 1955 -2107. ivThe computed aqueous CT mass flow rate across the water table for the modeled case is considerably larger than for imposed cases. The ...

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“…This includes an alternative to the most conservative assumption of complete advective transport of CCl 4 in Hanford groundwater (i.e., application of a 0 L/kg value of K d ). A most recent application of the experimentally derived desorption K d values (Riley et al 2005) was to the estimation of CCl 4 inventory in 200 West Area's unconfined aquifer (Murray et al 2006).…”

Section: K D Valuesmentioning

confidence: 99%

Carbon Tetrachloride Partition Coefficients Measured by Aqueous Sorption to Hanford Sediments from Operable Units 200-UP-1 and 200-ZP-1

Wellman¹,

Riley²,

Cordova³

et al. 2007

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In 2004, Fluor Hanford, Inc. (FHI) drilled several groundwater wells within the 200-UP-1 operable unit to monitor plumes that have been the focus of past remediation activities. Thirteen cores taken from three wells (699-30-66, 699-36-70B, and 299-W19-48) were sent to the Pacific Northwest National Laboratory (PNNL) for characterization and quantification of contaminant retardation. These cores were 4 inches in diameter by 6 inches in length, and were collected from depths near the unconfined-aquifer surface (water table) to locations approximately 150 to 180 feet below the water table. Additionally, in 2005 and 2006, FHI drilled several groundwater wells within the 200-ZP-1 operable unit to monitor plumes that have been the focus of past remediation activities. Twelve cores from split-spoon sampling of four of the wells (299-W11-43, 299-W11-86, 299-W14-71, and 299-W14-72) were sent to PNNL for quantification of carbon tetrachloride (CCl 4) sorption. These cores were 4 inches in diameter by 6 inches in length, and were collected from depths near the unconfined aquifer surface (water table) to locations approximately 450 feet below ground surface. Prior to this work, no site-specific adsorption data (i.e., values of distribution coefficient [K d ]) were available for the sediments or key contaminants present in the 200-UP-1 or 200-ZP-1 operable-unit groundwater plume. Selected physical and chemical characteristics of the sediments were determined (e.g., moisture content, particle size, specific surface area and carbon content). Site-specific sorption data for CCl 4 , with contact times from three to five days, was obtained with the < 2 mm size fractions of uncontaminated sediments taken from these boreholes and the partition coefficients (K d) determined. The magnitude of K d values was evaluated in the context of selected sediment characteristics and values of CCl 4 K d used in past Hanford assessments. Organic carbon content, known to influence the magnitude of K d values, was low in all sediments ranging from 0.02% to 0.04% in the less than 2 mm fraction. In some of the sediments, organic carbon content was below detection. Silt and clay surface areas ranged from 2 to 25 m 2 g-1. The CCl 4 K d values measured for the three 200-UP-1 sediments exhibited bimodal sorption with initial K d values (phase 1) ranging from 2.42 x 10-4 L Kg-1 to 3.20 x 10-4 L Kg-1 , and phase 2 values approximately 3.0 x 10-3 L Kg-1 for all sediments. Bimodal-sorption behavior was observed for three 200-ZP-1 sediments, which contained 0.03-0.04% organic carbon and a surface area > 2 m 2 g-1 for the silt and clay fraction. Phase 1 K d values measured for the eight 200-ZP-1 sediments ranged from 9.65 x 10-6 L Kg-1 to 5.21 x 10-5 L Kg-1. For those sediments exhibiting bimodal behavior, phase 2 K d values ranged from 1.17 x 10-4 L Kg-1 to 3.14 x 10-4 L Kg-1. Phase-1 200-UP-1 K d values were approximately 10 times higher than K d values measured for 200-ZP-1 sediments. Values of K d for sediments from 200-ZP-1 appeared to correlate with organ...

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Revised Geostatistical Analysis of the Inventory of Carbon Tetrachloride in the Unconfined Aquifer in the 200 West Area of the Hanford Site

Cited by 6 publications

References 15 publications

Hanford Site Vadose Zone Studies: An Overview

Hanford Site Vadose Zone Studies: An Overview

Modeling of Carbon Tetrachloride Flow and Transport in the Subsurface of the 200 West Disposal Sites: Large-Scale Model Configuration and Prediction of Future Carbon Tetrachloride Distribution Beneath the 216-Z-9 Disposal Site

Carbon Tetrachloride Partition Coefficients Measured by Aqueous Sorption to Hanford Sediments from Operable Units 200-UP-1 and 200-ZP-1

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