Near Surface Disposal Systems & Performance Craig H. Benson, University of Wisconsin ‐ Madison James H. Clarke, Vanderbilt University
Landfill Partnership C. Benson & J. Clarke, Leads Objective : Relevancy: • Science & technology relevant to DOE & • Decommissioning & remediation rely stakeholders needed to heavily on OSDFs. build confidence in on ‐ site • Cost effective design & construction of disposal facilities (OSDFs) OSDFs significantly affects cost & • Improve performance, schedule of projects. improve construction & operations efficiency, • Achieving stakeholder acceptance promote effective remains a major challenge due to lack monitoring, & lower costs. of confidence.
Barrier Systems Liners & covers of natural and synthetic materials Final Cover System MONITORING WELLS ACCESS ROAD W A S T E Liner System NAS (2009) ‐ knowledge of long ‐ term performance of waste containment structures as a principle science & technology gap for EM. Credibility gap for stakeholders . Figure courtesy M. Othman, Geosyntec Consultants
The Challenge – Confident Design for a Millennium ? Engineering Property ? Current Field As ‐ Built Research & ? Experience Prediction? Analogs? 100 1000 1 10 Time (years) 4
Strategic Approach Three Principles, Four Themes Theme 1. Long ‐ term field performance Three Principles: ‐ documenting field performance at full • Demonstrating efficacy of scale. current & proposed Theme 2. Prediction – evaluating & technology at field scale. parameterizing barrier models for • Understanding processes reliable prediction. & mechanisms that affect Theme 3. Barrier degradation – long ‐ term performance Defining barrier system degradation & • Evaluating predictive degradation mechanisms. capability, & enhancing , Theme 4. Surface barrier evolution ‐ models as needed to understanding how surface barriers more accurately reflect evolve & developing new approaches to reality. ensure adequate performance.
Research Thrusts in Theme 1: Understanding 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. 6
LLW Leachate Database – 1st Available Temporal Behavior: U and Tc 1x10 4 1x10 3 (a) (b) Concentration of Technetium (pCi/L) Concentration of Uranium ( µg/L) 1x10 3 1x10 2 1x10 2 1x10 1 1x10 1 OSDF OSDF ERDF ERDF EMWMF EMWMF ICDF ICDF 1x10 0 1x10 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Time (yr) Time (yr) 7
Research Thrusts in Theme 2 Evaluating & Developing Predictive Capability • Efficacy of contaminant transport models for barrier systems . • Evaluating how input uncertainty/sparseness affects uncertainty in model predictions. • Mechanistic description and measurement of radionuclide sorption & diffusion in barrier systems. Hg disposal/containment? 8
Composite Barrier Transport Model Validation – Independent Validation 50 (c) TCE Replicate 1 (depth=60mm) Replicate 2 (depth=60mm) Replicate 3 (depth=60mm) Foose et al. (2002) (depth=60mm) 40 POLLUTE (depth=60mm) Replicate 2 (depth=90mm) Foose et al. (2002) (depth=90mm) Concentration (mg/L) POLLUTE (depth=90mm) 30 20 10 0 0 50 100 150 200 250 300 350 400 Time (days) Forward “Class A” predictions using independently measured input parameters (not calibrated) 9
Research Thrusts in Theme 3 Understanding Barrier Degradation • Geomembrane degradation & life expectancy in LLW facilities. • Degradation of bentonite barriers due to ion exchange, hydration ‐ exchange kinetics, environmental stress (freezing, drying), concrete contact. 10
Geomembrane Lifetime Evaluation Time ‐ Temperature Superposition • Three temps (50, 70, 90 C) • Three solutions (DI, LLW, and LLW ‐ Rad) • 2 mm HDPE (ERDF, OSDF, OSDC). 180 Oxidation Induction Time (min) 170 160 150 140 130 40 50 60 70 80 90 100 11 Temperature ( o C)
Research Thrusts in Theme 4 Surface Barrier Evolution & Design • State ‐ of ‐ the ‐ art assessment of cover soil pedogenesis. • Design strategies that manage degradation & ensure adequate performance (e.g., evolutionary covers, surface treatments). 12
Coupling Hydrology & Erosion Control for Covers – Design Innovation 1000 Year Erosion - Vegetated Riprap Cover Semi-Arid Climate Resistive Cover Soil Profile 305 mm Cover top layer 150 mm Bedding layer (Rip-rap only) 610 mm Frost protection layer 610 mm Radon barrier 915 mm Transition layer Remaining Tailings 1 m 2 m 3 m 4 m 5 m 6 m Rip ‐ rap surface layer 7 m 13
Long Term Performance of Contaminant Isolation Systems Investigators: J.Clarke (Lead), M. Abkowitz, C. Benson, D. Kosson and J. Rustick, R. Worthy (graduate students) Project Objective : The overall goal of this project is the development of methodologies and analytical frameworks concerning performance assessment, design, monitoring, and maintenance of near surface contaminant isolation (CI) systems that will provide reliability, transparency, and traceability; enable risk-informed decision-making; and Accomplishments build confidence in containment approaches. “ Impact of Anthropogenic Climate Change on Near • Surface Disposal Facilities”, R. Worthy, Relevance and Impact to DOE: Technical and economic M. Abkowitz, C. Benson, J. Clarke, American limitations often require that contamination is isolated Nuclear Society Winter Meeting, November 2011. on-site through the use of engineered barriers (covers • “A Systems Approach to Determining Design and bottom liners) or excavated and moved to off-site Requirements for Near Surface Disposal” disposal facilities when contaminated sites are J. Rustick, J. Clarke and C. Benson, Invited remediated and nuclear facilities are decommissioned. Presentation to Washington State Department of Both engineered and institutional controls are needed Ecology Workshop on Barriers, February, 2012 . when contaminated materials and wastes are isolated 14 either in on-site or off-site disposal facilities.
Performance Assessment Components • Site Conceptual Models: – Link sources of contamination to potential receptors through environmental transport pathways and exposure routes • Performance Evaluation Scenarios: – Examine how the disposal facility could evolve over the life ‐ cycle of the facility • Event Tree Analysis: – Can be used to select performance evaluation scenarios 15 (Figure from the Ph.D. dissertation of Kevin Brown)
Examples of Influential Factors on NSDF Performance 16 Taken from INEEL/Ext ‐ 01 ‐ 01133, 2001
Examples of Sub ‐ Components For a Broad Systems Approach Design specific considerations: • – Type of engineered barriers to be used • Waste ‐ specific considerations: – Waste form – Waste package • Site ‐ specific considerations: Class A trench in 2008 – – Climate Barnwell LLW site – Geology – Ecology 17
The impact of Potential Climate Change and Episodic Events on the Performance of Near Surface Disposal Facilities • Natural and anthropogenic processes are believed to be causing climate change – rises in temperature – variations in precipitation patterns • Investigate near surface disposal facility hydrological parameters • Determine how these parameters influence water balance mechanisms (e.g., runoff, evapotranspiration (ET), percolation and storage). Focusing on the HELP model • • Uranium mill tailings disposal facility in Monticello, Utah – Average Annual Precipitation = 381 mm – Average Annual Temperature = 7.80 ° C 18
The Monticello Site Disposal cell completed in 2000 • • Layer 1: Fine ‐ textured soil and rock (water storage layer) • Layer 2: Sand layer (capillary barrier) • Layer 3: High ‐ density polyethylene geomembrane • Layer 4: Compacted soil liner (radon barrier) • Composite design regulated under RCRA Subtitle C and UMTRCA radon attenuation requirements
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