Written Closure, Post-Closure Care and Certification – Coal Combustion Waste Pond Closure, Southern Illinois

SCS Engineers provided closure support for the decommissioning of a former coal-fired power plant. Ash from the plant’s prior coal-burning operations was disposed in two ash-disposal ponds at the site. The ash ponds occupy approximately 60 acres.

SCS developed and submitted a closure plan for approval by the Illinois Environmental Protection Agency (IEPA). The closure plan included establishing a groundwater management zone within the areal extent of the two ponds. The closure plan prescribed the final cover system to be constructed in accordance with IEPA’s requirements and to control the groundwater management zone.

Our final cover system included the following components:

  • final grading layer comprised of the existing ash re-graded to promote positive drainage toward two storm water pump stations constructed as part of the closure
  • installation of a 40-mil high-density polyethylene (HDPE) geomembrane liner
  • installation of a geocomposite comprised of a HDPE geonet situated between two layers of geotextile
  • placement of 2.5 feet of compacted clay liner
  • placement of 6 inches of vegetative final cover
  • seeding and construction of final stormwater management controls

SCS performed construction quality assurance (CQA) services associated with the construction of the final cover system, including field testing the geomembrane panels and seams and compacted clay soils. SCS also provided CQA during the construction of the final stormwater controls, including new discharge outfalls to the adjacent Mississippi River.

SCS Engineers prepared the overall ash pond closure report for submittal to IEPA. The closure report includes documentation of the implemented CQA program, plus the summary and results of the tests performed. The closure report also includes a summary of the site’s hydrogeological conditions and groundwater management program, including groundwater monitoring and reporting results, monitoring well completion reports, and summary of statistical groundwater analysis.

The post-closure care plan we prepared serves as documentation for the final cover maintenance procedures and the groundwater monitoring requirements to be implemented at the site during the post-closure period.