Prairie Power Pearl Station ash pond closure

Project Summary

Hanson prepared plans and specifications for bidding and Illinois Environmental Protection Agency and Illinois Department of Natural Resources permitting documents required for a final cover system to close the 16-acre ash pond at the retired Prairie Power Inc. Pearl Station coal-fired plant.

Hanson’s team assisted with reviewing contractor bids, provided quality assurance construction observation and inspected disturbed areas of the construction site in accordance with General NPDES Permit No. ILR10. The design included site regrading, the installation of a high-density polyethylene geomembrane and 3 feet of soil cover. Hanson installed 10 groundwater monitoring wells to monitor the closure’s performance.  The final cover design included appropriate runoff controls for long-term stability and NPDES compliance, and it restricts surface water infiltration into the ash.

The closure was complicated by environmental regulations, groundwater impacts and the adjoining Illinois River. Hanson prepared a groundwater flow and contaminant transport model (using the U.S. Geological Survey’s MODFLOW and MT3D) to evaluate long-term closure performance. Hanson also reviewed the quarterly groundwater monitoring data and calculated background groundwater quality standards (parametric and nonparametric statistical calculations) to evaluate closure performance.

Construction was mandated to occur during the winter and spring, so Hanson has worked with the contractor to provide the redesign and testing of imported soil necessary to maintain the schedule despite weather conditions and flooding.