Use of Slurry Wall Systems to Support CCR Impoundment Closure and Corrective Action

摘要

Since the inception of the Resource Converstaton and Recovery Act(RCRA),soilbentonite slurry wall systems have received broad acceptance at environmentallyimpaired sites for managing and protecting groundwater.The broad-based applicability of these systems to provide site-specific variants for isolation,containment,and diversion of groundwater may serve as a valuable tool for coal combustion residuals(CCR)impoundment closure projects.The technology provides cost-effective support for both near-term impoundment dewatering programs,as well as future containment of impacted groundwater where may be appropriate for corrective action.Accordingly,slurry wall systems may provide a potentially valuable technology to consider for many pending closure programs.This paper provides an overview of the broad applications available for CCR-specific slurry wall programs,including the means of application in the field and the site factors that should be considered to define project-specific efficacy.In particular,three distinct technology applications for CCR impoundments have been highlighted herein.1.Impoundment Dewatering – Impermeable soil-bentonite barrier walls can be used to isolate impoundments and,thus,contain groundwater in contact with CCR materials.This impounded water can then be recovered using permeable infiltration gallery(s)constructed using similar slurry trenching methods.Where site conditions permit,this approach essentially converts the base of unlined impoundments into a subdrain system capable of accelerating the rate of lowering within the phreatic surface to increase in effective stresses,near-surface shear strength,and the ultimate bearing capacity.2.Corrective Action – Where corrective action may eventually be required,slurry wall systems provide an effective and positive means of groundwater containment,which eliminates routes of exposure to potential receptors.The isolation of potentially impacted groundwater within CCR impoundment footprints from external freshwater systems supports active various types of active remediation processes inside the containment while facilitating natural attenuation external to the containment barrier.In effect,such isolation interrupts the connection between the CCR source mass and groundwater,which isolates groundwater impacts so they can be addressed using active or passive recovery and treatment methods.3.Comprehensive Combined Groundwater Management System – Use of a soil-bentonite containment system early as part of impoundment closure can integrate immediate needs for dewatering with the longer-term goal of groundwater isolation,containment,and as appropriate,remediation.Such combined applications support a single expenditure to address both issues,which may reduce life-cycle closure costs.Therefore,early integration of such systems into closure plan designs may provide a financially-accretive reduction within overall life-cycle closure costs.