East Ash Pond 2 and East Ash Pond 4 Closure


Dynegy Midwest Generation


Hennepin, IL

CEC Services

  • Inactive CCR Impoundment Closure
  • Design & Permitting
  • Plans and Specifications
  • Geotechnical Engineering and Onsite Clay Borrow Evaluation
  • Stormwater Management/BMP Design
  • CQA Services
  • Construction Management

Owner Objective

Dynegy Midwest Generation (Dynegy) is a power generating company with facilities located in eight states. Dynegy planned the closure of inactive CCR impoundments in its fleet including East Ash Pond 2 (EAP 2) and East Ash Pond 4 (EAP 4) at Hennepin Station.

Starting in 2009, CEC designed a 25-year-capacity ash landfill to be constructed atop EAP2 and prepared the Initial Facility Report for permitting the ash landfill in accordance with Illinois Environmental Protection Agency (IEPA) regulations. Subsequently, CEC provided construction management and construction quality assurance services during construction of Phase 1 of the landfill and leachate pond, effectively closing 12 acres on the eastern side of EAP2.

CEC Approach

In 2016, CEC was tasked by Dynegy to prepare the engineering designs and permitting documents for the closure of EAP4, an inactive bottom ash pond, and the remaining 18-acres of EAP2.

Based on revised expectations for life of the power plant and beneficial reuse data, CEC initially resized the landfill air space requirements to determine the final landfill footprint over EAP2. CEC then completed the necessary engineering evaluations and prepared plans and technical specifications for closure of both inactive CCR impoundments.

Closure plans were accepted by the IEPA, allowing construction of the final caps to be constructed simultaneously starting in Spring 2020. CEC will provide assistance with contractor selections and during construction will providing engineering services in response to contractor RFI’s and design modifications.