The precipitation to the landfill cover is balanced by the combination of following effects: run-off, cumulating in soil, evapotranspiration, and percolation. For a given amount of precipitation, in order to reduce or eliminate percolation, the effects of run-off and/or evapotranspiration need to be enhanced.
Water harvesting uses runoff enhancement to manage landfill site water balance. This enhancement can be achieved by simply covering landfill cover surface with metal rain gutter placed parallel to the slope. The percentage of runoff increases when gutter coverage increases. However, too much coverage (> 40%) has little effect on runoff enhancement.
Vegetative cover reduces soil moisture via plant uptake and evapotranspiration. Plant cover also limits soil erosion. Vegetative cover is more stable because it emphasizes use of natural materials and configurations, which implies longevity.
Landfill cover enhancement is applicable for traditional landfills, surface impoundment’s, waste piles, sludges, and some mine tailings. It may prove to be less costly than a conventional barrier because it uses simple structure or local resources. It is simple in design, easy to install over an existing landfill cover, and easy to remove if other uses for the land emerge in the future.
Factors that may limit the applicability and effectiveness of these processes include:
- Proper site evaluation is required.
- Plant coverage is seasonal.
- Too much gutter coverage (> 40%) has little effect on runoff enhancement.
Landfill cover enhancement is a fairly new technology that is still being tested and demonstrated.
Naval Facilities Engineering Services Center initiated a demonstration project at Marine Corp Base Hawaii to evaluate infiltration control cover design. Metal rain gutters were placed on the ground surface and parallel to the slope.
Remaining surface was seeded with 6 native grasses and shrubs. After 9 months of operation, it was found that plots with runoff enhancement had 2 to 5 times more runoff, and 2 to 3 times less percolation.
The simple configuration of landfill cover enhancement should result better containment with little increase in costs. These costs are currently determined on a case-by-case basis because of construction material availability and design requirements at various site locations.