Groundwater Geochemistry Support for Alternative Source Demonstrations at CCR Facilities
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The (U.S. EPA) issued the Coal Combustion Residual (CCR) Rule in 2015 to regulate the location, design, and operation of CCR storage units such as landfills and ash ponds.

 

The CCR Rule requires the development of a monitoring well network to evaluate each regulated impoundment for releases by comparing downgradient groundwater quality to site-specific statistical background concentrations. If the results indicate that downgradient groundwater is elevated in the concentrations of select parameters, an alternative source demonstration (ASD) can be completed within 90 days of the exceedance to provide an explanation for these results other than a release from the regulated unit. Otherwise, the unit is forced into a more comprehensive monitoring program which can lead to an evaluation of corrective measures.  Based on our vast experience with CCR impacts to groundwater, the owner of several of these CCR impoundments retained Geosyntec to assist them with ASD development at 22 individual facilities. 

Geosyntec's Scope of Services

Geosyntec began each effort by completing a preliminary evaluation of the geochemistry to identify which were likely to have defensible ASDs.  Our evaluation included a review of multiple types of geochemical data, which resulted in our targeting seven units where an alternative source was identified.  The lines of evidence used to support the ASDs at each location were varied based on site conditions, and included:

  • A review of historic operations to identify unimpacted background concentrations prior to waste placement which indicated that boron and chloride are naturally present at higher concentrations in one geologic unit;
  • The development of a conceptual site model based on boring logs and groundwater concentrations which showed that dissolution of unweathered limestone downgradient of the storage pond resulted in elevated calcium and total dissolved solids concentrations;
  • Preparation of a one-dimensional model illustrating how the precipitation and subsequent dissolution of oversaturated calcite along the flow path beneath one landfill was contributing to elevated calcium concentrations and reduced pH at downgradient wells; and,
  • The use of next generation sequencing to characterize the microbial population in a well which identified a higher concentration of sulfur oxidizing bacteria that generate acid and drive down the groundwater pH as they metabolize.

Notable Accomplishments

Geosyntec successfully completed a preliminary evaluation at 22 different CCR units and prepared seven ASD reports within the allotted 90 day period.  Our preliminary evaluation allowed us to focus our resources on the ASDs most likely to be successful within the accelerated timeline required by the rule.  Each ASD report utilized a different line of evidence to provide strong support for the identified alternative source. Completion of these ASDs reduced sampling costs and prevented the initiation of more thorough monitoring requirements.

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Project Summary

  • Location: Various
  • Client: American Electric Power
  • Project Practice Areas: Water and Wastewater, Waste Management, Environmental Management
  • Type of Facility: CCR landfills
  • Services Provided: Geochemical analysis, One-dimensional transport modeling, Report preparation, Regulatory compliance, Alternative source demonstrations
  • Type of Work: Decommissioning and Demolition
  • Governing Regulation: Federal