Evoqua United States - Canada - EN

Modular cover helps town expand anaerobic sewer lagoon

Cover system divides existing aerated lagoon into two separate cells to accommodate for future growth

​Ranchester is a small town located in Sheridan County, Wyoming, USA, about nine miles (14 km) south of the Montana state line.


​As part of an upgrade to the town’s wastewater treatment facility, Ranchester was considering an expansion of its existing lagoon infrastructure to include anaerobic pre-treatment. The project involved dividing an existing aerated lagoon into two separate cells. The larger cell would remain aerated, and the new, somewhat smaller cell would then be used for anaerobic pre-treatment of the town’s wastewater. The change would help accommodate future growth of the town by nearly doubling the capacity of the aerated lagoon.

To complete the project, Ranchester needed an insulated cover system for the new anaerobic cell. Due to Ranchester’s northern climate and higher elevation (near 3,800 ft above sea level), this type of thermal protection is needed throughout the cold winters to maintain a sufficiently warm temperature in the anaerobic cell for treatment of the wastewater.


Evoqua’s Geomembrane Technologies custom-designed, fabricated, and installed a floating insulated modular cover system. They were selected for the project because of the ability to provide a design with the specific operating features required by the town. A long service life and low maintenance were also considered in the selection process.

The cover had to be designed as a removable system to allow for cleanout of the cell every few years. The insulated modular cover system was undoubtedly the best choice. The cover consists of a series of interconnected floating modules that, when combined, completely cover the water surface. The individual cover modules are anchored to the perimeter using weighted, UV-protected geomembrane skirting, which also provides protection against wind uplift.



​The new insulated modular cover system on Ranchester’s anaerobic lagoon helps the town retain heat for wastewater treatment year round—without restricting access for plant workers.

" They were able to design and install the cover to fit the conditions of the project. They were always available for questions and input, and did a great job with the installation. "

Chris Johnson, Engineer, Town of Ranchester

Installation of the insulated cover saved the town the cost of buying additional land and constructing additional lagoon cells by simply increasing the efficiency of their existing lagoon system. Evoqua’s Geomembrane Technologies™ brand innovative cover system floats, and is durable yet flexible, thus allowing it to easily accommodate varied water levels in the lagoon. It also provides access for future sludge removal. Under normal operating conditions, the cover system is also designed resists wind speeds of up to 70 mph.

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