MANAGING ASH POND CLOSURE WATERS

Philip Benson, Geosyntec Consultants, Inc.

Description

Managing Ash Pond Closure Waters: Technology Selection and Design Considerations Authors Mr. Philip Benson - United States - Geosyntec Consultants, Inc. Abstract The water management issues created by ash pond closure are complex. Dewatering activities can produce large volumes of water that require treatment. Pore water can contain high constituent concentrations due to the long- term contact with ash. Dewatering and stormwater management practices significantly impact the quantity and quality of water that must be treated. The ash has been deposited in the basin over years or even decades, often from diverse sources of coal. The diverse coal sources and natural ash aging can produce water that varies significantly in composition over the life of the closure project. Finally, discharge limitations can vary between facilities, depending on the assimilative capacity of the receiving body and whether technology-based effluent limitations or water quality-based effluent limitations are applied. These limitations could change again if portions of the dewatering effluents are determined to be leachate under the proposed Effluent Limitations Guidelines revisions. These factors need to be incorporated into the technology selection and subsequent design of water treatment systems for ash pond closure projects. It is critical that a robust water quality data set be collected and considered during technology selection and design. This paper will address design challenges and data requirements from both the constituent and technology standpoint. All ash pond closure projects are regulated for pH and total suspended solids (TSS). Many are also regulated for trace metals, such as copper, zinc, arsenic, and selenium. Examples that will be discussed include managing flow variability, accounting for TSS loadings and water chemistry in determining the right clarification and filtration strategy, understanding the role of oxidation state in arsenic and selenium treatability, and understanding water chemistry constraints and interferences on biological treatment, ion exchange, and zero discharge technologies.

 
May 14th, 2:00 PM May 14th, 2:30 PM

MANAGING ASH POND CLOSURE WATERS

Grand Rapids, Michigan

Managing Ash Pond Closure Waters: Technology Selection and Design Considerations Authors Mr. Philip Benson - United States - Geosyntec Consultants, Inc. Abstract The water management issues created by ash pond closure are complex. Dewatering activities can produce large volumes of water that require treatment. Pore water can contain high constituent concentrations due to the long- term contact with ash. Dewatering and stormwater management practices significantly impact the quantity and quality of water that must be treated. The ash has been deposited in the basin over years or even decades, often from diverse sources of coal. The diverse coal sources and natural ash aging can produce water that varies significantly in composition over the life of the closure project. Finally, discharge limitations can vary between facilities, depending on the assimilative capacity of the receiving body and whether technology-based effluent limitations or water quality-based effluent limitations are applied. These limitations could change again if portions of the dewatering effluents are determined to be leachate under the proposed Effluent Limitations Guidelines revisions. These factors need to be incorporated into the technology selection and subsequent design of water treatment systems for ash pond closure projects. It is critical that a robust water quality data set be collected and considered during technology selection and design. This paper will address design challenges and data requirements from both the constituent and technology standpoint. All ash pond closure projects are regulated for pH and total suspended solids (TSS). Many are also regulated for trace metals, such as copper, zinc, arsenic, and selenium. Examples that will be discussed include managing flow variability, accounting for TSS loadings and water chemistry in determining the right clarification and filtration strategy, understanding the role of oxidation state in arsenic and selenium treatability, and understanding water chemistry constraints and interferences on biological treatment, ion exchange, and zero discharge technologies.