Coffeen Power Plant antidegradation study and wastewater treatment

Project Summary

Future coal combustion residual (CCR) surface impoundment closures at the Coffeen Power Plant in Coffeen, Illinois, required dewatering of the in-place CCR materials and the removal of free water (unwatering) prior to construction of a final cover system in accordance with the federal CCR rule.

To assist with a required National Pollutant Discharge Elimination System permit application, Hanson performed an antidegradation study to discharge two new contributory wastewater streams after treatment to Coffeen Lake. The antidegradation study was needed for a modification to the permit that would allow the discharge of the dewatering waters to Coffeen Lake.

Hanson’s scope of services consisted of a planning document outlining a proposed treatment process for the removal of dissolved iron in the dewatering water of ash ponds 1 and 2 at the power plant. The document outlined a proposed treatment method for removing the iron, a proposed timeline for the dewatering water in the landfills based on estimates of 105 million combined gallons from ash ponds 1 and 2 and an average iron concentration of 138.41 mg/L.

Hanson also performed services related to the treatment of discharge water associated with the dewatering and unwatering of ash ponds 1 and 2 at the power plant. In discussions with Vistra staff, the Illinois Environmental Protection Agency draft permit modification for the ash ponds’ dewatering and unwatering treat the discharges as point sources. The point sources required sampling for compliance prior to discharge into the plant cooling water discharge flume, as opposed to at the weir at the lake end of the discharge flume.

Hanson reviewed the discharge parameters for the draft permit modification for the dewatering and unwatering and available water quality data for surface and porewater of ash ponds 1 and 2. Hanson also reviewed treatment alternatives for water from Ash Pond 2 and evaluated treatment alternatives for Ash Pond 1.