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Acquisition of porous media saturated hydraulic conductivity data in the laboratory is usually time consuming and costly because of the manual labor associated with the currently available techniques. Lately, there has been increased interest in automating hydraulic conductivity laboratory techniques to reduce analysis time and improve data consistency. A new apparatus was developed that is able to measure hydraulic conductivity values with the constant-flux, constant-head, and falling-head methods in a fully automated fashion. The apparatus can be used for both packed columns and undisturbed field cores. The column design is such that water is forced to flow in a nominally one-dimensional manner through the porous medium. An analysis is initiated with a "smart search," yielding an estimate of the saturated hydraulic conductivity. The operator can use this estimated value to obtain conductivity values using one, two, or all three methods. Besides installing and removing the columns, no manual efforts are required. Hydraulic conductivity data for standard laboratory sands showed that application of the three methods resulted in similar results, indicating that external flow resistance was small. A comparison with literature data for the same sands, obtained with a constant-flux method, showed differences

The steel container and vitrified waste materials that comprise waste packages planned for subsurface disposal of low-activity wastes at Hanford are subject to corrosion processes that generate a net volumetric expansion. Stress state and deformation in an idealized disposal system were modeled as a function of expansion pressure. Potential expansion pressures from glass and steel corrosion product formation were estimated and compared with the computed critical inner pressures ( P c ) required to induce mechanical instability. Even a moderate degree of steel corrosion was found to generate internal pressures significantly above P c . However, a kinetics analysis suggests that between 270 and 2500 years would be required before the P c is exceeded.

An analytical solution technique was developed for one-dimensional, steady vertical water flow in variably saturated, layered soils with arbitrary hydraulic properties. The solution technique is based on the exact integral solution for the Gardner exponential hydraulic conductivity function. The exact solution is extended for use with arbitrary hydraulic property functions, or measured K(h) data, by approximating ln K(h) with piecewise-linear curve segments and integrating analytically, segment by segment. The resulting analytical solution technique is accurate, computationally efficient, and applicable to unsaturated and/or saturated conditions. Several application examples are presented, including a comparison with earlier experimental results.

Some of the defense wastes at the Hanford Site in southeastern Washington State are stored in the vadose zone. It is possible that natural recharge could mobilize and transport the contaminants in these wastes to the groundwater, as well as influence groundwater velocities and directions. The objective of this study was to estimate the areal distribution of natural recharge for use as a boundary condition for a groundwater flow and transport model. A geographic information system (GIS) was used to identify all possible combinations of soil type and vegetation and assign to each an appropriate estimate of recharge. The strategy was to assign estimates based on field data and supplement with simulation results only when necessary. The estimated rates varied from 0.7 to 127.1 mm/yr. The order of preference for assigning estimates was lysimetry > water content measurements > tracers > modeling, based on qualitative estimates of the relative error of each method as applied.The GIS software was used to estimate the annual recharge volume attributable to specific soil-vegetation combinations. The total annual recharge volume was 8.47 x 10' L for the 765 km 2 portion of the site containing the major waste storage areas. This volume is from 2 to 10 times higher than estimates of runoff and groundwater flow from adjacent higher elevations and is equivalent to facility discharges in 1992. The recharge map showed the impact of a 1984 fire on increasing recharge ; it also illustrated the higher recharge rates associated with disturbed soils in the waste storage areas.

The Brooks-Corey and van Genuchten functions were modified to adequately represent retention at all matric suctions. The modification consisted of replacing the residual water content with an adsorption equation (Campbell and Shiozawa, 1992). The modified functions retain the form of the original functions in the wet range and the form of an adsorption equation in the dry range. The modified functions provided excellent fits to data from six soils with textures ranging from sand to silty clay. The modified van Genuchten function can use previously determined parameters to obtain a reasonable representation of the high matric suction range, thus allowing for the use of existing parameter sets. The modified functions, as well as the function proposed by Rossi and Nimmo (1994), were combined with the Mualem conductivity model to generate closed-form analytical expressions for the calculation of hydraulic conductivity.

Surface covers are used to isolate contaminants in hazardous and low-level radioactive sites for time frames ranging from hundreds of years to millennia or more. In the absence of data for such durations, the long-term performance of surface barriers can only be represented with short-term tests or inferred from analogs and modeling. This paper provides evidence of field performance of soil covers for periods up to 17 yr. The results of lysimeter studies from a semiarid site in Washington State show that a cover design known as the Hanford Barrier, which consists of 1.5 m of silt loam above a sand-gravel capillary break, can nearly eliminate drainage. The results were similar if plants were present or not, demonstrating the robustness of the design. Furthermore, reducing the silt loam thickness to 1.0 m (as might occur via erosion), with or without plants, did not lead to drainage. When irrigated to mimic 3× average precipitation conditions, the vegetated Hanford Barrier continued to prevent drainage. Overall, the results showed no loss in performance during the 17 yr of testing. Only when plants were eliminated completely from the 3× precipitation test did drainage occur (rates ranged from 6 to 16 mm yr -1 ). In a separate test, replacing the top 0.2 m of silt loam with dune sand and reducing the plant cover did not lead immediately to the onset of drainage, but soil matric heads within the silt loam noticeably increased. This observation suggests that dune sand migration onto a surface cover has the potential to reduce a cover's ability to minimize deep drainage.

The UNSAT-H model was developed at Pacific Northwest National Laboratory (PNNL) to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. To achieve the above goals for assessing water dynamics and estimating recharge rates, the UNSAT-H addresses soil water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow. The UNSAT-H model simulates liquid water flow using the Richards equation, water vapor diffusion using Fick's law, and sensible heat flow using the Fourier equation. This report documents UNSAT-H Version 3.0. The report includes the bases for the conceptual model and its numerical implementation, benchmark test cases, example simulations involving layered soils and plants, and the code manual. Version 3.0 is an enhanced-capability update of UNSAT-H Version 2.0 (Fayer Jones 1990). New features include hysteresis, an iterative solution of head and temperature, an energy balance check, the modified Picard solution technique, additional hydraulic functions, multiple year simulation capability, and general enhancements. This report includes eight example problems. The first four are verification tests of UNSAT-H capabilities. The second four example problems are demonstrations of real-world situations.

In FY 1996, the Pacific Northwest National Laboratory (PNNL) provided technical assistance to Battelle Columbus Operations (BCO) in their ongoing assessment of contaminant migration at the Pantex Plant in Amarillo, Texas. The objective of this report is to calculate deep drainage rates at the Pantex Plant. These deep drainage rates may eventually be used to predict contaminant loading to the underlying unconfined aquifer for the Pantex Plant Baseline Risk Assessment. These rates will also be used to support analyses of remedial activities involving surface alterations or the subsurface injection withdrawal of liquids or gases. The scope of this report is to estimate deep drainage rates for the major surface features at the Pantex Plant, including ditches and playas, natural grassland, dryland crop rotation, unvegetated soil, and graveled surfaces. Areas such as Pantex Lake that are outside the main plant boundaries were not included in the analysis. All estimates were derived using existing data or best estimates; no new data were collected. The modeling framework used to estimate the rates is described to enable future correlations, improvements, and enhancements. The scope of this report includes only data gathered during FY 1996. However, a current review of the data gathered on weather, soil, plants, and other information in the time period since did not reveal anything that would significantly alter the results presented in this report.

Computer simulations were performed to assess the performance of the waste-form-alone (WFA) design for the low-activity-waste (LAW) disposal system. In FY 1997, PNNL performed additional simulations for Lockheed Martin Hanford Company (LMHC) to address specific questions about the disposal. LMHC manages the Glass Performance Assessment Project for DOE. The objectives of the additional simulations were to demonstrate the impact of grid resolution, diffusion, fracture flow within the waste form, and consumption of water by the waste form. It was assumed that the waste form would be the only part of the engineered disposal system that inhibits radionuclide release, referred to as WFA assumption. All calculations were performed with the latest version of the STOMP (Subsurface Transport Over Multiple Phases) simulator. Multiple simulations of the WFA disposal were performed to identify parameter and conceptual model sensitivities. The corrosion rate, recharge rate, well interception factor, hydraulic properties, and hydraulic and retardation models were shown to be important. Diffusion was shown to be important for the gravel model of glass but not the soil model. The impact of temperature changes was discussed and determined to be negligible. Water consumption during corrosion was evaluated and found to have a minimal effect on the dosemore » calculations. Fracture flow within the glass was evaluated and found to have only a minimal effect on the dose calculations.« less

This report describes a modeling effort to provide a computer simulation capability for estimating the distribution and movement of moisture in the saltcake-type waste contained in Hanford`s single-shell radioactive waste storage tanks. This moisture model goes beyond an earlier version because it describes water vapor movement as well as the interstitial liquid held in a saltcake waste. The work was performed by Pacific Northwest National Laboratory to assist Duke Engineering and Services Hanford with the Organic Tank Safety Program. The Organic Tank Safety Program is concerned whether saltcake waste, when stabilized by jet pumping, will retain sufficient moisture near the surface to preclude any possibility of an accidental ignition and propagation of burning. The nitrate/nitrite saltcake, which might also potentially include combustible organic chemicals might not always retain enough moisture near the surface to preclude any such accident. Draining liquid from a tank by pumping, coupled with moisture evaporating into a tank`s head space, may cause a dry waste surface that is not inherently safe. The moisture model was devised to help examine this safety question. The model accounts for water being continually cycled by evaporation into the head space and returned to the waste by condensation or partly lost through venting to the external atmosphere. Water evaporation occurs even in a closed tank, because it is driven by the transfer to the outside of the heat load generated by radioactivity within the waste. How dry a waste may become over time depends on the particular hydraulic properties of a saltcake, and the model uses those properties to describe the capillary flow of interstitial liquid as well as the water vapor flow caused by thermal differences within the porous waste.

The current preferred method for disposal of low-level radioactive waste (LLW) at the Hanford Site is to vitrify the wastes so they can be stored in a near-surface, shallow-land burial facility (Shord 1995). Pacific Northwest Laboratory (PNL) managed the PNL Vitrification Technology Development (PVTD) Project to assist Westinghouse Hanford Company (WHC) in designing and assessing the performance of a disposal facility for the vitrified LLW. Vadose zone flow and transport models are recognized as necessary tools for baseline risk assessments of stored waste forms. The objective of the Controlled Field Testing task of the PVTD Project is to perform and analyze field experiments to demonstrate the appropriateness of conceptual models for the performance assessment. The most convincing way to demonstrate appropriateness is to show that the model can reproduce the movement of water and contaminants in the field. Before expensive new experiments are initiated, an injection experiment conducted at the Hanford Site in 1980 (designated the ``Sisson and the Lu experiment``) should be completely analyzed and understood. Briefly, in that test, a solution containing multiple tracers was injected at a single point into the subsurface sediments. The resulting spread of the water and tracers was monitored in wells surrounding the injection point. Given the advances in knowledge, computational capabilities, and models over the last 15 years, it is important to re-analyze the data before proceeding to other experiments and history-matching exercises.

In 1994, the Pacific Northwest Laboratory (PNL) initiated the Recharge Task, under the PNL Vitrification Technology Development (PVTD) project, to assist Westinghouse Hanford Company (WHC) in designing and assessing the performance of a low-level waste (LLW) disposal facility for the US Department of Energy (DOE). The Recharge Task was established to address the issue of ground water recharge in and around the LLW facility and throughout the Hanford Site as it affects the unconfined aquifer under the facility. The objectives of this report are to summarize the current knowledge of natural ground water recharge at the Hanford Site and to outline the work that must be completed in order to provide defensible estimates of recharge for use in the performance assessment of this LLW disposal facility. Recharge studies at the Hanford Site indicate that recharge rates are highly variable, ranging from nearly zero to greater than 100 mm/yr depending on precipitation, vegetative cover, and soil types. Coarse-textured soils without plants yielded the greatest recharge. Finer-textured soils, with or without plants, yielded the least. Lysimeters provided accurate, short-term measurements of recharge as well as water-balance data for the soil-atmosphere interface and root zone. Tracers provided estimates of longer-term average recharge rates in undisturbed settings. Numerical models demonstrated the sensitivity of recharge rates to different processes and forecast recharge rates for different conditions. All of these tools (lysimetry, tracers, and numerical models) are considered vital to the development of defensible estimates of natural ground water recharge rates for the performance assessment of a LLW disposal facility at the Hanford Site.

The Ground-Water Surveillance Project monitors the distribution of contaminants in ground water at the Hanford Site for the U.S. Department of Energy. A subtask called {open_quotes}Water Budget at Hanford{close_quotes} was initiated in FY 1994. The objective of this subtask was to produce a defensible map of estimated recharge rates across the Hanford Site. Methods that have been used to estimate recharge rates at the Hanford Site include measurements (of drainage, water contents, and tracers) and computer modeling. For the simulations of 12 soil-vegetation combinations, the annual rates varied from 0.05 mm/yr for the Ephrata sandy loam with bunchgrass to 85.2 mm/yr for the same soil without vegetation. Water content data from the Grass Site in the 300 Area indicated that annual rates varied from 3.0 to 143.5 mm/yr during an 8-year period. The annual volume of estimated recharge was calculated to be 8.47 {times} 10{sup 9} L for the potential future Hanford Site (i.e., the portion of the current Site bounded by Highway 240 and the Columbia River). This total volume is similar to earlier estimates of natural recharge and is 2 to 10x higher than estimates of runoff and ground-water flow from higher elevations. Not only is the volume more » of natural recharge significant in comparison to other ground-water inputs, the distribution of estimated recharge is highly skewed to the disturbed sandy soils (i.e., the 200 Areas, where most contaminants originate). The lack of good estimates of the means and variances of the supporting data (i.e., the soil map, the vegetation/land use map, the model parameters) translates into large uncertainties in the recharge estimates. When combined, the significant quantity of estimated recharge, its high sensitivity to disturbance, and the unquantified uncertainty of the data and model parameters suggest that the defensibility of the recharge estimates should be improved. « less

The In Situ Remediation Integrated Program (ISRIP) was established by the US Department of Energy (DOE) to advance the state-of-the art of innovative in situ remediation technologies to the point of demonstration and to broaden the applicability of these technologies to the widely varying site remediation requirements throughout the DOE complex. This program complements similar ongoing integrated demonstration programs being conducted at several DOE sites. The ISRIP has been conducting baseline assessments on in situ technologies to support program planning. Pacific Northwest Laboratory conducted an assessment and evaluation of subsurface containment barrier technology in support of ISRIP`s Containment Technology Subprogram. This report summarizes the results of that activity and provides a recommendation for priortizing areas in which additional research and development is needed to advance the technology to the point of demonstration in support of DOE`s site restoration activities.

Numerical models are used to predict the fate of contaminants in the environment for durations of 10,000 years and more. At the Hanford Site, these models are being used to evaluate the potential health effects and environmental impacts associated with the disposal of double-shell tank waste in grouted vaults. These models require information on the properties of the earthen and manufactured materials that compose the vault system and its surroundings. This report documents the physical and hydraulic properties of the materials associated with burial of grouted double-shell tank waste at the Hanford Site.

Radioactive waste exists at the US Department of Energy's (DOE's) Hanford Site in a variety of locations, including subsurface grout and tank farms, solid waste burial grounds, and contaminated soil sites. Some of these waste sites may need to be isolated from percolating water to minimize the potential for transport of the waste to the ground water, which eventually discharges to the Columbia River. Multilayer protective barriers have been proposed as a means of limiting the flow of water through the waste sites (DOE 1987). A multiyear research program (managed jointly by Pacific Northwest Laboratory (PNL) and Westinghouse Hanford Company for the DOE) is aimed at assessing the performance of these barriers. One aspect of this program involves the use of computer models to predict barrier performance. Three modeling studies have already been conducted and a test plan was produced. The simulation work reported here was conducted by PNL and extends the previous modeling work. The purpose of this report are to understand phenomena that have been observed in the field and to provide information that can be used to improve hydrologic modeling of the protective barrier. An improved modeling capability results in better estimates of barrier performance. Better estimatesmore » can be used to improve the design of barriers and the assessment of their long-term performance.« less

An attempt has been made to test the validity of a two-dimensional model of soil-water dynamics in a sloping field, with respect to groundwater level fluctuations during several infiltration-drainage cycles. The data from rain recorders, runoff plots, water table wells, tensiometers, and an evaporation pan were used to describe the various initial and boundary conditions. Soil hydraulic properties were determined from undisturbed cores and in situ methods. Comparisons of the predicted and measured water table positions were used to judge the model's capabilities. After two one-week periods of no rainfall, during which the actual water table fell 11 and 79 cm, the predicted water table levels were within 1.5 and 8 cm, respectively, of the measured levels. Before and immediately after periods of rainfall, the predicted water table levels were usually within 2 cm of the measured levels. As the water table rose in response to the rainstorm, however, the predicted rise was only one-half that measured in the field. Altering the shape of the moisture characteristic programmed in the model nearly doubled the predicted rise. Hence the discrepancy between prediction and observation may be due to insufficient accuracy in determination of the soil moisture characteristic in the very wet range, or to failure to account for air occlusion or hysteresis.

Waste mangement practices at the Hanford Site have relied havily on near-surface burial. Predicting the future performance of any burial site in terms of the migration of buried contaminants requires a model capable of simulating water flow in the unsaturated soils above the buried waste. The model currently being developed to meet this need is UNSAT-H, which was developed at Pacific Northwest Laboratory for assessing the water dynamics of near-surface waste-disposal sites at the Hanfrod Site. The code will primarily be used to predict deep drainage (i.e., recharge) as a function of environmental conditions such as climate, soil type, and vegetation. UNSAT-H will also simulate various waste-management practices such as placing surface barriers over waste sites. UNSAT-H is a one-dimensional model that simulates the dynamics processes of infiltration, drainage, redistribution, surface evaporation, and uptake of water from soil by plants. UNSAT-H is designed to utilize two auxiliary codes. These codes are DATAINH, which is used to process the input data, and DATAOUT, which is used to process the UNSAT-H output. Operation of the code requires three separate steps. First, the problem to be simulated must be conceptualized in terms of boundary conditions, available data, and soil properties. Next, the datamore » must be correctly formatted for input. Finally, the unput data must be processed, UNSAT-H run, and the output data processed for analysis. This report includes three examples of code use. In the first example, a benchmark test case is run in which the results of UNSAT-H simulations of infiltration are compared with an analytical solution and a numerical solution. The comparisons show excellent agreement for the specific test case, and this agreement provides vertification of the infiltration portion of the UNSAT-H code. The other two examples of code use are a simulation of a layered soil and one of plant transpiration.« less

This report documents progress for the following major research projects: stabilization, engineering, and monitoring alternatives assessment for improving regulation of uranium recovery operations and waste management; attenuation of radon emission from uranium tailings; assessment of leachate movement from uranium mill tailings; and methods of minimizing ground-water contaminants from in-situ leach uranium mining.

Protective barriers are being considered for use at the Hanford Site to enhance the isolation of radioactive wastes from water, plant, and animal intrusion. This study assesses the effectiveness of protective barriers for isolation of wastes from water. In this report, barrier designs are reviewed and several barrier modeling assumptions are tested. 20 refs., 16 figs., 6 tabs.

The unsaturated soil moisture flow code, UNSAT-H, which was developed at Pacific Northwest Laboratory for assessing water movement at waste sites on the Hanford site, is documented in this report. This code is used in simulating the water dynamics of arid sites under consideration for waste disposal. The results of an example simulation of constant infiltration show excellent agreement with an analytical solution and another numerical solution, thus providing some verification of the UNSAT-H code. Areas of the code are identified for future work and include runoff, snowmelt, long-term climate and plant models, and parameter measurement. 29 refs., 7 figs., 2 tabs.