Tuesday, September 19, 2017

Coal Ash Impoundments—Cap or Move?

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EPRI Tool Helps Evaluate Best Course of Action

A new EPRI tool can provide utilities with a comprehensive understanding of the impacts of closing coal ash surface impoundments, guiding more effective decision making.

With recent federal regulatory actions and the retirement of power plants, coal ash impoundments are closing at an unprecedented rate. Utilities have two options:

  • Cap the impoundment.
  • Excavate, transport, and dispose of the ash in a lined landfill; then refill the former impoundment.

Closing in place can reduce—but does not always eliminate—leaching of toxic contaminants from the impoundment to groundwater. Removing ash can eliminate future leaching, but it involves significantly more construction, with greater impacts to air quality and community safety. Removing ash often takes longer and can result in significant leaching during excavation. Balancing the relative advantages and disadvantages of the two options is complex, requiring input from various experts.

EPRI’s Relative Impact Framework tool provides a way to organize and effectively analyze the expert input.

“EPRI developed this tool because our utility members were asking for a method to scientifically evaluate different alternatives for closing their coal ash facilities,” said EPRI Principal Technical Leader Bruce Hensel.

The framework guides the user through a series of steps to quantitatively assess:

  • Impacts to groundwater and surface water
  • Impacts to air quality
  • Probability of accidents
  • Energy consumption, water use, and other impacts on natural resources

After EPRI tested the tool on a hypothetical site, it worked with Tennessee Valley Authority (TVA) to demonstrate its use with 10 TVA impoundments.

“We saw using EPRI’s tool as an opportunity to inform our decision with respect to each impoundment,” said TVA Senior Program Manager Anne Aiken.

TVA included the analyses in an Environmental Impact Statement, but the schedule did not provide time sufficient to collect all the data necessary for a full quantitative assessment. As an alternative, EPRI and TVA developed a method to qualitatively analyze the relative impacts of options for the TVA impoundments. After EPRI used the tool to quantitatively assess the hypothetical impoundment, the characteristics of the TVA impoundments were compared with those of the hypothetical site. Once the differences between the TVA sites and the hypothetical site were established, the results from the assessment of the hypothetical site were adjusted to account for the conditions at the TVA sites. The tool helped TVA with elements of its Environmental Impact Statement and provided additional credibility.

For closing in place, the analyses found that removing the water and capping the impoundments would reduce groundwater contamination and structural stability risks. Compared with ash removal, closing in place presented significantly lower risks related to workforce health, safety, and transportation (such as crashes, derailments, and road damage).

TVA elected to close all 10 impoundments in place and identified measures to minimize potential adverse impacts, including dust control systems, erosion and sediment control to protect surface waters from construction impacts, and revegetation with native species.

“The framework supports simple to complex modeling approaches to determine the impacts to groundwater, surface water, and air,” said Aiken. “Closure timelines can play an important role in the impacts.”

“The tool provides a way to organize and present information on multiple environmental media in a way that makes sense to people,” said Hensel. “It serves as a guide for making logical yet difficult decisions. This in-depth investigation can be expensive, but is a small fraction compared to the overall cost of either closure alternative.”

For its work applying the tool, TVA won a 2016 EPRI Technology Transfer Award.

Key EPRI Technical Experts:

Bruce Hensel