Grant Township considers lagoon liners
COPPER HARBOR — Because of the failure of the liner of the wastewater treatment lagoon at Copper Harbor, the Department of Environmental Quality (DEQ), has recommended the liners in both the primary and secondary lagoons be replaced, Grant Township Supervisor Ken Stigers said during the regular meeting Tuesday.
The recommendation is in consideration of the age of the liners.
The life expectancy of a wastewater lagoon liner is approximately 20 years if it is buried, and two years if it is not, according to several sources.
In the case of the Grant Township wastewater treatment facility in Keweenaw County, the two lagoons in Copper Harbor were constructed in 1993.
The liners in the lagoons are buried, said Zane Hyrkas, engineer with OHM of Hancock. The method of burial was to lay down a five-inch deep layer of sand over which the liner was placed. It was then buried under five additional inches of sand.
“The existing liner is a 40-mil PVC liner,” Hyrkas explained. “The new liner system will be a geosynthetic, combined liner system, a geosynthetic clay liner and a PVC or PHC liner, basically acting as two separate liners.”
A PVC (polyvinyl chloride) liner is a flexible plastic geomembrane that has a high puncture strength and is resistant to abrasion. Due to its flexibility, PVC liners conform to sub-grade contours, such as lagoons, and they prevents contaminants from entering groundwater sources or streams.
While using two liners will not increase the lifespan of either, greatly increases the chances of containment should one fail.
A geosynthetic clay liner are composites geotextile and betonite composites sandwiched between to layers of geotextile, and are engineered for many different environmental containment applications, such as landfills,
Geosynthetic clay liners are geotextile and bentonite composites (typically sodium bentonite sandwiched between two layers of geotextile), engineered for a variety of environmental containment applications.
Geotextiles offer a long-lasting resistance to physical or chemical breakdown in harsh elements, while the bentonite’s high swelling capacity and low permeability provide an effective hydraulic seal, according to nylex.com.
The use of two liners in the lagoons will not increase the lifespan of either, but it help ensure there are no future leaks from the lagoons.