Landfill Capping with Woodland Ecosystems

Abstract

As the field of phytoremediation has evolved over the last 10 years, there has been a growing interest in the use of vegetative covers as alternative landfill caps. Consequently, a number of vegetative caps (grass, shrubs, and trees) have been installed at landfills across the United States, with tree caps being the focus of this paper. The two primary objectives of vegetative caps are to minimize water percolation into landfill waste via a “sponge and pump” mechanism and to prevent surface soil erosion. The soil pores hold precipitation like a sponge until plant roots can access the water; plants take up this water for growth and release it into the atmosphere by transpiration. The erosion control objective is achieved by canopy interception of rainfall, minimizing the “splash effect,” and the growing of a root matrix that interlaces through soil particles. Secondary benefits of vegetative caps include aesthetic appeal for the neighboring community, sequestration of greenhouse gases, reduced construction costs, reduced operation costs, and creation of wildlife habitat. When properly designed and managed, vegetative caps can minimize landfill owner liability while creating a future asset for the surrounding community. The Ecolotree Cap (ECap) (Ecolotree, Inc., North Liberty, Iowa) is a patented phytoremediation system that consists of carefully designed cover soils planted with perennial trees and understory grasses. This system has been installed at 13 landfills in the United States (in nine states) and at one landfill in Europe (Slovenia). The sites include pre-Subtitle D landfills, Subtitle D demonstrations, a construction debris landfill, and a landfill on the Superfund National Priorities List. The ECap cover is currently being evaluated for Subtitle D landfill closure at two sites by the U.S. Environmental Protection Agency Alternative Cover Assessment Program.