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Interstate Engineering was retained by Dakota Municipal Solid Waste Landfill to provide bidding assistance, design, and construction observation services for the Landfill. When the project began in the spring of the year, the landfill retained Interstate for Cell 4 Sideslope Liner, and Phase IB Final Cover construction. The landfill contracted geosynthetic materials and installation with GSE Lining Technology.
The Cell 4 Sideslope consisted of a composite liner including 2 feet of clay, a 60-mil HDPE geomembrane, non-woven geotextile and 12 inches of granular drainage layer. The final cover consisted of 1.5 feet of clay, 40-mil LLDPE, 200-mil geocomposite drainage material, 12 inches of rooting layer, and 6 inches of topsoil. Two 36-inch diameter gas vent wells were also drilled.
As the project continued, the Landfill also requested that Interstate add Cell 5 Liner design and construction to the schedule. Cell 5 was unusually challenging due to its shape. It shares a leachate sump with future Cell 6, and is built around wetland setbacks. The design required 10 slopes and eight leachate cleanouts within a 6.5 acre footprint. The construction of liner and final cover will have a combined total of approximately 17 acres for the three projects which were completed on schedule.