skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: E-Area LLWF Vadose Zone Model: Probabilistic Model for Estimating Subsided-Area Infiltration Rates

Abstract

A probabilistic model employing a Monte Carlo sampling technique was developed in Python to generate statistical distributions of the upslope-intact-area to subsided-area ratio (Area UAi/Area SAi) for closure cap subsidence scenarios that differ in assumed percent subsidence and the total number of intact plus subsided compartments. The plan is to use this model as a component in the probabilistic system model for the E-Area Performance Assessment (PA), contributing uncertainty in infiltration estimates.

Authors:
 [1];  [1]
  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
Publication Date:
Research Org.:
Savannah River Site (SRS), Aiken, SC (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1414386
Report Number(s):
SRNL-STI-2017-00729
DOE Contract Number:
AC09-08SR22470
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
97 MATHEMATICS AND COMPUTING

Citation Formats

Dyer, J., and Flach, G. E-Area LLWF Vadose Zone Model: Probabilistic Model for Estimating Subsided-Area Infiltration Rates. United States: N. p., 2017. Web. doi:10.2172/1414386.
Dyer, J., & Flach, G. E-Area LLWF Vadose Zone Model: Probabilistic Model for Estimating Subsided-Area Infiltration Rates. United States. doi:10.2172/1414386.
Dyer, J., and Flach, G. 2017. "E-Area LLWF Vadose Zone Model: Probabilistic Model for Estimating Subsided-Area Infiltration Rates". United States. doi:10.2172/1414386. https://www.osti.gov/servlets/purl/1414386.
@article{osti_1414386,
title = {E-Area LLWF Vadose Zone Model: Probabilistic Model for Estimating Subsided-Area Infiltration Rates},
author = {Dyer, J. and Flach, G.},
abstractNote = {A probabilistic model employing a Monte Carlo sampling technique was developed in Python to generate statistical distributions of the upslope-intact-area to subsided-area ratio (AreaUAi/AreaSAi) for closure cap subsidence scenarios that differ in assumed percent subsidence and the total number of intact plus subsided compartments. The plan is to use this model as a component in the probabilistic system model for the E-Area Performance Assessment (PA), contributing uncertainty in infiltration estimates.},
doi = {10.2172/1414386},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month =
}

Technical Report:

Save / Share:
  • The overall objectives of the treatability test is to evaluate and optimize polyphosphate remediation technology for infiltration either from ground surface, or some depth of excavation, providing direct stabilization of uranium within the deep vadose and capillary fringe above the 300 Area aquifer. Expected result from this experimental plan is a data package that includes: 1) quantification of the retardation of polyphosphate, 2) the rate of degradation and the retardation of degradation products as a function of water content, 3) an understanding of the mechanism of autunite formation via the reaction of solid phase calcite-bound uranium and aqueous polyphosphate remediationmore » technology, 4) an understanding of the transformation mechanism, identity of secondary phases, and the kinetics of the reaction between uranyl-carbonate and –silicate minerals with the polyphosphate remedy under solubility-limiting conditions, 5) quantification of the extent and rate of uranium released and immobilized based on the infiltration rate of the polyphosphate remedy and the effect of and periodic wet-dry cycling on the efficacy of polyphosphate remediation for uranium in the vadose zone and capillary fringe, and 6) quantification of reliable equilibrium solubility values for autunite under hydraulically unsaturated conditions allowing accurate prediction of the long-term stability of autunite. Moreover, results of intermediate scale testing will quantify the transport of polyphosphate and degradation products, and yield degradation rates, at a scale that is bridging the gap between the small-scale UFA studies and the field scale. These results will be used to test and verify a site-specific, variable saturation, reactive transport model and to aid in the design of a pilot-scale field test of this technology. In particular, the infiltration approach and monitoring strategy of the pilot test would be primarily based on results from intermediate-scale testing. Results from this experimental plan will be documented in a PNNL report.« less
  • A simple one-dimensional isothermal and vertical vadose zone steady-state infiltration or evaporation model is proposed. The model is built on the principle of the balance of liquid water and water vapor flux. The mechanical movement of air in the soil is assumed negligible. The user may select from one of four van Genuchten water release forms; I=0, I=1, I=2, and I=3. The most often used form corresponds to I=0. The water vapor movement portion has been adapted from D. A. Rose. The nonlinear steady-state distribution of moisture tension is obtained via a Newtonian iterative method for either a given positivemore » infiltration or a negative evaporation value. Several realistic simulations are discussed. 21 refs., 10 figs., 7 tabs.« less
  • The Multimedia Environmental Pollutant Assessment System (MEPAS) is an objective, scientific methodology to assess and prioritize hazardous chemical and radionuclide waste disposal sites based on a limited amount of site information. The vadose zone/groundwater transport module (RADCON) of MEPAS was enhanced to simulate scenarios where water-infiltration barriers (caps) have been emplaced over contaminated sites. The computer code was modified to accommodate three periods of constant water flux through the vadose zone (i.e., flux with no cap, fully functioning cap, and partially failed cap). The simulation results from test problems where the cap should have no effect essentially duplicated the simulationmore » results from the same test problems evaluated with the earlier (baseline) version of RADCON (which requires a single constant value of water flux). Therefore, MEPAS assessments of baseline (no-cap) scenarios should be the same as they were when the baseline RADCON code was used as the vadose zone/groundwater transport module. As expected, simulations of preliminary test problems where the cap should have an effect showed that peak concentrations arrived at the receptor later and were reduced in magnitude compared to the no-cap case. Simple criteria were derived to indicate the degree to which results could be affected by violation of the assumptions of the conceptual model. However, even when assumptions are violated, errors on the nonconservative side that could occur as the cap fails should be offset by errors on the conservative side that would have already occurred as the cap was emplaced, resulting in simulations that are conservative overall.« less
  • This report represents a synthesis and integration of basic and applied research into a system-scale model of the Hanford 300 Area groundwater uranium plume, supported by the U.S. Department of Energy’s Richland Operations (DOE-RL) office. The report integrates research findings and data from DOE Office of Science (DOE-SC), Office of Environmental Management (DOE-EM), and DOE-RL projects, and from the site remediation and closure contractor, Washington Closure Hanford, LLC (WCH). The three-dimensional, system-scale model addresses water flow and reactive transport of uranium for the coupled vadose zone, unconfined aquifer, and Columbia River shoreline of the Hanford 300 Area. The system-scale modelmore » of the 300 Area was developed to be a decision-support tool to evaluate processes of the total system affecting the groundwater uranium plume. The model can also be used to address “what if” questions regarding different remediation endpoints, and to assist in design and evaluation of field remediation efforts. For example, the proposed cleanup plan for the Hanford 300 Area includes removal, treatment, and disposal of contaminated sediments from known waste sites, enhanced attenuation of uranium hot spots in the vadose and periodically rewetted zone, and continued monitoring of groundwater with institutional controls. Illustrative simulations of polyphosphate infiltration were performed to demonstrate the ability of the system-scale model to address these types of questions. The use of this model in conjunction with continued field monitoring is expected to provide a rigorous basis for developing operational strategies for field remediation and for defining defensible remediation endpoints.« less
  • In preparation for the next revision of the E-Area Low-Level Waste Facility (LLWF) Performance Assessment (PA), a mass balance model was developed in Microsoft Excel to confirm correct implementation of intact- and subsided-area infiltration profiles for the proposed closure cap in the PORFLOW vadose-zone model. The infiltration profiles are based on the results of Hydrologic Evaluation of Landfill Performance (HELP) model simulations for both intact and subsided cases.