Design and Installation of a Permeable Treatment Wall at the DOE West Valley Site Lisa Durham Argonne National Laboratory
DOE West Valley Site IDN and ENVIRONET Training Course Western New York Nuclear Service Center (WNYNSC) ~56 km south of Buffalo, New York New York State Energy Research and Development Authority (NYSERDA) 1,300 April 2012 hectares Argonne National Laboratory, USA
West Valley Site Layout & History ~200 Acres Nation's only commercial nuclear fuel reprocessing facility Reprocessing ceased in 1972 Decontamination and decommissioning now focus Environmental contamination predominately Cs-137 in surface soils and Sr-90 in groundwater
Groundwater Problem Immediate Concern Significant Sr-90 release to shallow groundwater from beneath the main plant in 1968 Groundwater flow to the east/northeast following site topography Groundwater discharges to streams and via seeps/springs along the northern, northeastern, and eastern portions of the site Sr-90 contamination followed groundwater and began appearing in surface water features (streams and seeps) Site under pressure to stop the movement of contaminated groundwater 4
IDN and ENVIRONET Training Course
General Geology Greatly Incised Bedrock Valley Layered and Variably Textured Glacial Sediments Plant Site on Upland Plateau (sand & gravel) Surrounding Creeks In Down Cut Valleys Groundwater Discharges to Drainages & Seeps Sr-90 Transport Dominates Plume Vertical Aquitard of Lavery Till Lower Boundary of Sand & Gravel
Site-Specific Geology Paleo-thalweg in SWS
Site-specific Geology Hydrostatigraphy: 1. Fill (Reworked Site Soils and Facility Construction Spoils) 2. Thick Bedded Unit (TBU) Coarse-grained, Loose Sandy Gravel, Thickly Bedded 3. Slack-water Sequence (SWS) Banded Layering (macro-varves), Clean Sand & Gravel Layers Seasonally Variable Groundwater Heads (TBU Very Reactive) Vertical Groundwater Gradients Vary: Plant Area (Downward, TBU to SWS) Pump & Treat Area (Slightly Upward, SWS to TBU) Plateau Edge (Generally Coincident) Paleo-thalweg in SWS Hydraulic Conductivity 10E-4 to 10E-2 cm/s, Preferential Flow Zones 10E-2
A - A IDN and ENVIRONET Training Course Geologic Cross Sections B - B
Groundwater Flow
Phased Investigations of Source 1994 & 1997 Geoprobe Investigations Under and Near Main Plant Better Defined Layered Hydrogeology 1. Fill 2. Thick Bedded Unit (TBU) 3. Slack-water Sequence (SWS) SWS Transports Sr-90 (100K to 1M pci/l)
Prior Actions Pilot scale permeable treatment wall attempted results were inconclusive Pump and treat system installed (several extraction wells connected to a water treatment system) Expensive to maintain and operate No apparent appreciable impact on migration of the Sr-90 plume 12
Remedial Action Objectives (RAO)
Alternative Assessment Seven Alternatives Were Screened IDN and ENVIRONET Training Course Configurations Included: o Interceptor Trench Drains o Pump & Treat o Active Permeable Treatment Wall (PTW) o Passive PTW Preferred Remedy: o Passive PTW North of 10,000 pci/l Isopleth
Clinoptilolit e
Why Clinoptilolite Media Competitive cation exchange Sorption mechanism is competitive ion exchange Capacity for Sr sorption is dependent on presence of competing cations, particularly Ca 2+ and Mg 2+ Diffusion to interior of zeolite particles may be rate-limiting under higher flow rates 16
UB Lab Testing of Sr Sorption and Exchange
IDN and ENVIRONET Training Course
PTW-area Design Data Collection
PTW-area Plume Refinement
Design Modeling for Hydraulic Capture MODFLOW Groundwater Modeling Two Layer Model Concern With Nearly 7-ft Head Differential Along Wall Predicted Plume Capture - MODPATH
PTW Design Data Install Along Access Road 850-feet Long 19- to 30-feet Deep Minimally 3-feet Wide
Installation Method DeWind One-pass Trencher Installation Concept ~200,000 Pounds With Two 1,000 hp Diesels Cutting Bar 30-ft Long, 39-in Wide, Studded With Titanium Tipped Teeth Media Deployed by 8-ft to 4-ft Long Trench Box Attached to Hopper
Zeolite Handling 2,300 Supersacks of 1-ton Each 60-bag Lots for CEC Analyses QA Samples to Ensure No Mechanical Degradation Stone Slinger Trucks With Bag Cutters Deliver Zeolite to Trencher (hopper feed)
Above Grade Soil Spoils Containment Wooden "A-Frame Construction 36 inches wide at the base 5 ft. tall, spaced on 1 ft. centers Covered with sheeting Lined with 60 mil. membrane
Soil Spoils Handling Custom Side-chute Conveyor Removes Cuttings and Lifts to Soil Containment Structure
Trencher Set-up Actions IDN and ENVIRONET Training Course Starter Trench and Set Up Titanium Teeth Configured for Upward and Outward Removal (chevron)
Trencher Operational 1. Stone Slinger Feeds Front Hopper 2. Zeolite Transferred to Top-end Conveyors 3. Zeolite Delivered to Trencher Hopper 4. Gravity Deployment While Crawling 5. Trench Box Maintains Opening 6. Zeolite Left Behind as Competent Wall
Installation Success Optimal Delivery Rate ~120 ft/day Excellent Deployment and Coverage Exposed Zeolite Allowed Pre-cover Inspection
Performance Monitoring Array
Wall Performance to Date Wall in place for more than a year Sr-90 activity concentrations in groundwater immediately upgradient from the wall slowly increasing Sr-90 activity concentrations in groundwater within the wall either below detection limits or much lower than up-gradient Sr-90 activity concentrations immediately down-gradient from the wall slowly decreasing No evidence that the wall is impeding groundwater flow There is evidence the wall is acting as a giant french drain, moving groundwater from the west end towards the east end (not necessarily a bad thing) 31
Project Success Stories 1. First of a kind full-scale zeolite PTW installed with one-pass trencher technology. 2. Fall-season installation provided weather-related challenges. 3. ZERO lost-time accidents under tight schedules and design corrections 4. Partnering with UB and Dewind One-pass Trenching to optimize zeolite selection and installation method 5. Zeolite volume contingency was revisited during project to lessen impact on installation schedule 6. Field modifications to zeolite feed method at end of project increased operational efficiency (lesson learned for future work-zone designs) 7. Post-installation drilling and sampling showed highly successful deployment of zeolite (i.e., no voids, hydrodynamic pinching, or partial filling)
IDN and ENVIRONET Training Course