Signe K. Wurstner

Transient Inverse Calibration of Hanford Site-Wide Groundwater Model to Hanford Operational Impacts - 1943 to 1996

This report describes a new initiative to strengthen the technical defensibility of predictions made with the Hanford site-wide groundwater flow and transport model. The focus is on characterizing major uncertainties in the current model. PNNL will develop and implement a calibration approach and methodology that can be used to evaluate alternative conceptual models of the Hanford aquifer system. The calibration process will involve a three-dimensional transient inverse calibration of each numerical model to historical observations of hydraulic and water quality impacts to the unconfined aquifer system from Hanford operations since the mid-1940s.

Transient Inverse Calibration of Site-Wide Groundwater Model to Hanford Operational Impacts from 1943 to 1996--Alternative Conceptual Model Considering Interaction with Uppermost Basalt Confined Aquifer

The baseline three-dimensional transient inverse model for the estimation of site-wide scale flow parameters, including their uncertainties, using data on the transient behavior of the unconfined aquifer system over the entire historical period of Hanford operations, has been modified to account for the effects of basalt intercommunication between the Hanford unconfined aquifer and the underlying upper basalt confined aquifer. Both the baseline and alternative conceptual models (ACM-1) considered only the groundwater flow component and corresponding observational data in the 3-Dl transient inverse calibration efforts. Subsequent efforts will examine both groundwater flow and transport. Comparisons of goodness of fit measures and parameter estimation results for the ACM-1 transient inverse calibrated model with those from previous site-wide groundwater modeling efforts illustrate that the new 3-D transient inverse model approach will strengthen the technical defensibility of the final model(s) and provide the ability to incorporate uncertainty in predictions related to both conceptual model and parameter uncertainty.

Uncertainty Analysis Framework - Hanford Site-Wide Groundwater Flow and Transport Model

Pacific Northwest National Laboratory (PNNL) embarked on a new initiative to strengthen the technical defensibility of the predictions being made with a site-wide groundwater flow and transport model at the U.S. Department of Energy Hanford Site in southeastern Washington State. In FY 2000, the focus of the initiative was on the characterization of major uncertainties in the current conceptual model that would affect model predictions. The long-term goals of the initiative are the development and implementation of an uncertainty estimation methodology in future assessments and analyses using the site-wide model. This report focuses on the development and implementation of an uncertainty analysis framework.

GS3: A Knowledge Management Architecture for Collaborative Geologic Sequestration Modeling

Modern scientific enterprises are inherently knowledge-intensive. In general, scientific studies in domains such as geoscience, chemistry, physics and biology require the acquisition and manipulation of large amounts of experimental and field data in order to create inputs for large-scale computational simulations. The results of these simulations must then be analyzed, leading to refinements of inputs and models and further simulations. In this paper we describe our efforts in creating a knowledge management platform to support collaborative, wide-scale studies in the area of geologic sequestration modeling. The platform, known as GS3 (Geologic Sequestration Software Suite), exploits and integrates off-the-shelf software components including semantic wikis, content management systems and open source middleware to create the core architecture. We then extend the wiki environment to support the capture of provenance, the ability to incorporate various analysis tools, and the ability to launch simulations on supercomputers. The paper describes the key components of GS3 and demonstrates its use through illustrative examples. We conclude by assessing the suitability of our approach for geologic sequestration modeling and generalization to other scientific problem domains.

2005 Closure Assessments for WMA-C Tank Farms: Numerical Simulations

In support of CH2M HILL Hanford Group, Inc.s (CHG) closure of the Hanford Site Single-Shell Tank (SST) Waste Management Area (WMA) tank farms, numerical simulations of flow and solute transport were executed to investigate different potential contaminant source scenarios that may pose long-term risks to groundwater from the closure of the C Tank Farm. These simulations were based on the initial assessment effort (Zhang et al., 2003), but implemented a revised approach that examined a range of key parameters and multiple base cases. Four different potential source types were identified to represent the four base cases, and included past leaks, diffusion releases from residual wastes, leaks during retrieval, and ancillary equipment sources. Using a two-dimensional cross section through the C Tank Farm (Tanks C-103–C-112) and a unit release from Tank C-112, two solutes (uranium-238 (U-238) and technetium-99 (Tc 99)) were transported through the problem domain. To evaluate the effect of sorption on contaminant transport, seven different sorption coefficients were simulated for U 238. Apart from differences in source releases, all four base cases utilized the same median parameter values to describe flow and contaminant transport at the WMA C. Forty-six additional cases were also run that examined individual transport responses to the upper and lower limits of the median parameter values implemented in the base case systems. For the conservative solute, Tc-99, results amongst the base cases showed that the simulations investigating past leaks demonstrated the highest peak concentrations and the earliest arrival times (48 years) due to the proximity of the plume to the water table and the high recharge rate before surface barriers were installed. Simulations investigating leaks during retrieval predicted peak concentrations ~60 times smaller than the past leak cases, and corresponding arrival times that occurred ~70 years later. The diffusion release base case predicted the lowest peak concentrations and arrival times for all solutes. Even after 10,000 years of simulation, only 11.2% of the Tc-99 mass migrated past the fence line compliance point in the groundwater. Although ancillary equipment cases released the contaminant at a similar depth as the diffusion cases, nearly all of the Tc-99 (99.0%) exited the groundwater domain by the end of the simulation due to differences in release rates. These differences were also reflected in the peak arrival times, which were ~8,500 years for the diffusion base case, and ~3,700 years for the base ancillary equipment release. In the diffusion cases, peak concentration predictions were sensitive to the rate of diffusion, but had no impact on the peak concentration arrival times. The average peak concentration was ~3.2 times higher than the base case value for the upper estimate of diffusion, and 3.2  10-3 lower for the lower bounding estimate. The past leak, ancillary equipment and retrieval leak cases were sensitive to the estimate of the pre-barrier installment recharge rate. For example, on average for the past leaks, relative concentrations increased by ~2.2 times for the upper recharge estimate, and decreased by ~0.14 times for the lower bound. Faster arrival times were associated with the upper recharge estimate, and slower arrival times with the lower estimate. Similar trends in both predicted peaks and arrival times occurred for the ancillary equipment and retrieval leaks scenarios that investigated the uncertainty in the pre-barrier installment recharge rate. Uncertainty in the plume depth also impacted predicted peak concentrations and arrival times for the past leak scenario. Trends similar to the pre-barrier installment recharge rate resulted, with higher concentrations and earlier breakthroughs associated with a lower plume depth, and lower concentrations and later breakthroughs with a higher plume depth.

Groundwater Flow and Transport Calculations Supporting the Immobilized Low-Activity Waste Disposal Facility Performance Assessment

This report summarizes the Hanford Site-Wide Groundwater Model and its application to the Immobilized Low-Activity Waste (ILAW) Disposal Facility Performance Assessment (PA). The site-wide model and supporting local-scale models are used to evaluate impacts from the transport of contaminants at a hypothetical well 100 m downgradient of the disposal facilities and to evaluate regional flow conditions and transport from the ILAW disposal facilities to the Columbia River. These models were used to well-intercept factors (WIFs) or dilution factors from a given areal flux of a hypothetical contaminant released to the unconfined aquifer from the ILAW disposal facilities for two waste-disposal options: (1) a remote-handled trench concept and (2) a concrete-vault concept. These WIFs are being used in conjunction with calculations of released contaminant fluxes through the vadose zone to estimate potential impacts from radiological and hazardous chemical contaminants within the ILAW disposal facility at compliance points.

Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site, Southeast Washington

A composite analysis of low-level radioactive waste disposal and other radioactive sources was recently completed for the Hanford Site in Southeast Washington State. Impacts from source release and environmental transportwere estimated for a 1 000-year period following Site closure in a multi-step process involving 1) estimation of radiological inventories and releases, 2) assessment of contaminant migration through the vadose zone, groundwater, and atmospheric pathways, 3) and estimation of doses. The analysis showed that most of the radionuclide inventory in past-practice liquid discharge sites and pre-1988 solid waste burial grounds on the 200 Area Plateau will be released in the first several hundred years following Hanford Site closure, well before projected releases from active and planned disposals of solid waste. The maximum predicted agricultural dose was less than 6 mrem/y in 2050 and declined thereafter. The maximum doses for the residential, industrial, and recreational scenarios, were 2.2, 0.7, and 0.04 mrem/y, respectively, and also declined after 2050.

Addendum to Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site

This report summarizes efforts to complete an addendum analysis to the first iteration of the Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site (Composite Analysis). This document describes the background and performance objectives of the Composite Analysis and this addendum analysis. The methods used, results, and conclusions for this Addendum analysis are summarized, and recommendations are made for work to be undertaken in anticipation of a second analysis.