Closure Options Archives - Moretrench

Cap In Place

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Where water levels are close to the pond surface, predrainage dewatering of the ash is essential to create a surface crust that will safely support construction equipment in order to perform cuts and fills and place a cap. Due to the variability of the ash, the thickness of the crust that will be required will vary from pond to pond, and should be evaluated with a pilot dewatering test prior to the start of construction. Permanent subsurface cut-off barriers can be installed to prevent the off-site movement of water. Embankment stability, utility support, and protection of outfall pipes can be achieved through a number of ground improvement techniques such as jet grouting and ground freezing.

Clean Closure

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Stabilizing ash ponds using predrainage dewatering for safe and efficient ash removal presents very specific challenges. The interaction of the ash pond with the surrounding aquifer, ponds or cooling water channels and the potential impact of any “hidden” external sources of water recharge, such as old stream beds or springs, must be thoroughly investigated and understood. A small amount of inflow into the base of the pond can render a tremendous amount of ash unstable. To ensure safe excavation and removal of the ash thorough drainage is essential. Adequate site characterization, most effectively accomplished with pilot dewatering tests is necessary for an effective plan. With a finite amount of compliance time remaining, early action is both prudent and cost effective.

Overview

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To comply with EPA-mandated regulations for the closure of coal ash impoundments, ash drainage is required for either clean closure or cap in place to safely execute closure plans. Water treatment, perimeter cutoff barriers, and dam/levee rehabilitation will also be necessary for the compliant closure of most ponds.

No other contractor has greater experience in stabilizing ash and industrial by-product than Moretrench. Our engineering and operations teams work closely with Owners, Engineers and General Contractors to develop and implement plant-specific closure plans.