Background

In 2015, when sludge stability and odors became an issue, Foth assisted the Winnebago County Solid Waste Management Board (a Foth client since 1989) by developing a site stabilization and odor control plan. Foth developed a stabilization plan that included the installation of drain piping and dewatering sumps, development of containment structures, stabilizing the sludge surface with temporary cover, and reducing odors. Foth implemented the stabilization plan including construction of the dewatering structures, gas control equipment, and placement of coal combustion fly ash to cover and strengthen the sludge surface. In November 2016, the Sludge Landfill ceased accepting paper mill sludge waste and Foth provided final cover design, bidding support, and construction documentation services for the closure activities.

Approach

Foth designed a fly ash cover installed from the perimeter inward to contain the sludge. Use of the perimeter drains allowed liquid to be removed as the sludge was covered with fly ash and began to consolidate.
Foth conducted field and lab testing on different sludge and ash mixtures to establish a 1:1 ratio that allowed the Sludge Landfill operators to achieve better placement and compaction of the daily sludge disposal operations.

Results

WCSWMB and Foth established a temporary capping layer of fly ash and bottom ash that not only stabilized the sludge surface, but the ash was brought in as a beneficial use material that allowed WCSWMB to capture value of the air space used by the ash.
The sumps were designed to allow temporary pumping of liquid if it became necessary to supplement the gravity system. This feature proved valuable to help remove liquid at various sump locations as the project proceeded.
Foth coordinated the cover tie-in so that only small areas of cover soils were removed for the geomembrane connections at one time. Soil materials were strategically placed to manage run-off as the tie-in connections were made. These methods minimized the risk of sludge displacement during construction.
Using a combination of active gas collection and solar vent flares is helping to both control odors and allow the operators to minimize oxygen intrusion into the gas system and potential impact, to the gas to energy facility