Research on Engineered Barrier Technology by CRESP's Landfill Partnership Craig H. Benson, PhD, PE, DGE Wisconsin Distinguished Professor University of Wisconsin-Madison/CRESP 1

On-Site Disposal Facility (OSDF): aka LLW or MW Landfill Final Cover System Liner System MONITORING WELLS Figure courtesy M. Othman, Geosyntec Consultants

The Challenge – Confident Design for a Millennium Engineering Property Time (years) As-Built Current Field Research & Experience ? ? ? Analogs

Purpose of Landfill Partnership 4 Conduct independent applied research to address landfill technology issues that cross- cut the DOE complex. Provide forum to discuss regulatory conflicts and shortcomings, and to recommend technological solutions. Participate in independent technical reviews related to DOE technologies or sites.

Relevance 5 OSDFs (landfills) are key step in D&D/restoration at EM sites; stakeholder concerns regarding long-term performance impede acceptance/permitting. NAS (2009) identifies existing knowledge on long-term performance of waste containment structures as a principle science and technology gap for EM. Credibility gap for stakeholders. LP to provide source terms for EM’s ASCEM (analogous to CBP).

Technical Priorities to Build Confidence 1.Develop confidence in the long-term (1000 yr) performance of OSDF designs. 2.Understanding of degradation mechanisms affecting containment systems in OSDFs. 3.Understand and quantify how final covers evolve over the design life of OSDFs. 4.Develop confidence in models used for PAs of OSDFs and characterize uncertainty in predictions. 5.Create and evaluate monitoring strategies that build confidence in the performance of OSDFs. 6

Approach to Build Technical Confidence Understand our existing technology – does it work as well as we predict? Understand how barriers degrade or evolve over time so that we can make confident long- term predictions. Develop reliable methods (e.g., computer tools) to predict performance in as-built state, and as barrier degrades. 7

1. Understanding our Existing Technology State-of-the-art: knowledge base from field studies of barrier performance. – Resistive barrier technologies – Water balance barrier technologies State-of-the-art: lessons learned from field studies of cover soil pedogenesis. Leachate source terms for LLW disposal facilities. 8

2. Developing Prediction Methods Mechanistic description of radionuclide sorption and diffusion in barrier systems. Assessing methods to measure radionuclide sorption and diffusion in barrier systems Accounting for large-particle effects in soil water retention. Efficacy of transport models for predicting transport through barrier systems. Evaluating how input uncertainty/sparseness affects uncertainty in model predictions. 9

3. Understanding Barrier Degradation Geomembrane degradation & life expectancy in LLW facilities. Degradation of bentonite barriers due to ion exchange, hydration-exchange kinetics, and environmental stress (freezing, drying). Degradation of bentonite barriers exposed to concrete surfaces. Design strategies that manage degradation & ensure adequate performance (e.g., evolutionary covers, surface treatments). 10

11 Speculative discussion at Paducah in March ‘11. Literature suggests lifespan may be more than 1000 yr. No data for conditions in LLW or MW facilities. No credible scientific data for LLW or MW to draw inference, but methods from solid waste literature Geomembrane Degradation

Durability Tests in Synthetic LLW Leachate 12 Three temperatures (50, 70, & 90 C) Three solutions (DI, LLW, and LLW- Rad) 2 mm HDPE (ERDF, OSDF).

Parameters LLW Average Synthetic Target TOC (mg/L)7.738 Reduction Potential (mV) pH7.217 Inorganic Macrocomponents (mM/L) Calcium3.714 Magnesium4.495 Sodium Potassium Sulfate Chloride4.75 Nitrate/Nitrite Alkalinity Metals (mM/L) Aluminum Arsenic Barium Copper Iron Lithium Manganese Strontium Zinc Radionuclides (ERDF Ave) Uranium (µg/L) H-3 (pCi/L) Tc-99 (pCi/L)730800

Geomembrane Incubators

Major Cations in LLW Leachate 15

Radionuclides: U and Tc 16

Temporal Behavior: U and Tc 17

Temporal Behavior: Sr and Tritium 18

Coupling Hydrological & Erosion Control on Covers 19 Used Cheney Disposal Facility (Grand Junction, CO) as base case SIBERIA landform evolution model (1000 yr simulation) SVFLUX variably saturated flow model for hydrology.

Erosion on Rip-Rap Covers 20 Rip-rap surface layer

21 Gravel Admixture Topsoil Surface Layer Coupling Hydrological & Erosion Control on Covers: Gravel Admixture Cover

Hydrological Prediction for Grand Junction, CO 22 Gravel admixture covers have net release to atmosphere Rip-rap covers harvest water – collect and drain into waste. Similar efficacy for erosion control! Flow Into Waste Flow Out of Waste

Transport Parameters for Barriers 23 Diffusion and sorption tests for geomembranes. Evaluating new geomembrane with exceptionally low radon diffusion coefficient.

Transport Prediction for Barriers 24

Prediction - TCE Transport in Clay Barrier 25 Forward “Class A” predictions using independently measured input parameters (not calibrated)

Summary Remarks Independent basic to applied research focused on developing confidence in containment facilities. Focus on topics that our stakeholders indicate are important. Assess full-scale facilities and near full-scale demonstrations, understand fundamental mechanisms, and create/validate predictive models. 26