Lubbock’s Caliche Canyon Landfill (TCEQ MSW #0069) included a 45-acre cell with a prescriptive final cover designed with earthen and geomembrane components equal to the bottom liner system. From the surface to the waste mass, the prescriptive cover included a 6 to 10-inch thick soil erosion cover, an 18-inch thick compacted soil layer and a 60-millimeter HDPE geomembrane layer. Construction of this type of cover system is difficult for several reasons, one being that the geomembrane is easily punctured. Even with careful precautions, cover leaks through geomembranes punctures are likely.

PSC’s solution was to utilize local sandy soils and eliminate the need for expensive imported clays and geomembranes. The end result was an elegant balance between soil porosity, thickness and vegetation. Working with all three of these parameters a cover was constructed that not only met, but exceeded EPA regulations for final cover infiltration rates. This type of final cover was an Evapotranspiration (ET) Cover – or more commonly known as a Water Balance Cover.

The ET Cover designed for Lubbock was a 3-foot thick soil liner comprised exclusively from onsite soils. The liners were constructed in three, separate 12-inch thick loose lifts on top of a prepared subgrade. The ET cover was seeded with a blended mix of native grasses intended to provide a vegetation cover that will thrive during any weather condition.