Effectiveness of Various CCP Unit Closure Strategies

Cole Mayer, WSP USA
PJ Nolan, WSP USA
Mark Haney, WSP USA
Marc Okin, NiSource, Inc

Description

Power utilities are increasingly challenged by regulatory agencies to implement remediation strategies that anticipate long-term changes to groundwater quality in response to closure activities. Unanticipated changes to site geochemistry during closure can have unforeseen impacts leading to groundwater impairments caused by leaching of Coal Combustion Product (CCP) constituents. In some cases, the cessation of recharge flux may even further inhibit the natural rehabilitation of a site by further shifting it from natural conditions. Here we present an evaluation of multiple closure scenarios where 3-D reactive geochemical modeling was used to evaluate constituent flux and concentration downgradient of the unit. Modeling identified that there was no measurable difference in time to achieve compliance at downgradient monitoring wells when comparing 90% to 100% ash removal. Additionally, modeling identified the current regulator-approved closure approach of 90% closure-by-removal with the addition of a cap on the CCP unit results in an equal if not better reduction in flux and improvement in groundwater quality than 100% closure-by-removal. Thus, the current regulator-approved strategy is the most appropriate for achieving groundwater compliance.

 
May 15th, 1:00 PM May 15th, 1:30 PM

Effectiveness of Various CCP Unit Closure Strategies

Grand Rapids, Michigan

Power utilities are increasingly challenged by regulatory agencies to implement remediation strategies that anticipate long-term changes to groundwater quality in response to closure activities. Unanticipated changes to site geochemistry during closure can have unforeseen impacts leading to groundwater impairments caused by leaching of Coal Combustion Product (CCP) constituents. In some cases, the cessation of recharge flux may even further inhibit the natural rehabilitation of a site by further shifting it from natural conditions. Here we present an evaluation of multiple closure scenarios where 3-D reactive geochemical modeling was used to evaluate constituent flux and concentration downgradient of the unit. Modeling identified that there was no measurable difference in time to achieve compliance at downgradient monitoring wells when comparing 90% to 100% ash removal. Additionally, modeling identified the current regulator-approved closure approach of 90% closure-by-removal with the addition of a cap on the CCP unit results in an equal if not better reduction in flux and improvement in groundwater quality than 100% closure-by-removal. Thus, the current regulator-approved strategy is the most appropriate for achieving groundwater compliance.