Can you imagine spending a million dollars on a lawn mower? Unfortunately, many responsible parties are doing just that — practically speaking — because, during the landfill cap design process, proper consideration was not given to the cost of the long-term post-closure maintenance requirements of the vegetative support layer.
The primary purpose of the vegetation layer is to protect the underlying drainage & low permeability cap layers. Those layers divert clean rainwater away from the landfill waste, thereby reducing pollution, potential environmental impacts, and environmental liability. Planting of a non-native, cool weather grass is a quick and easy way to stabilize a newly capped landfill. However, these quick growing grass vegetative support layers are proving to be expensive to maintain and not effective in providing long-term protection of the landfill cap system.
It is clearly time to re-evaluate that practice of using non-native cool weather grass for vegetating closed landfills.
Vegetative support layers comprised of non-native, cool weather grasses do not have a good long-term performance track record. These grasses are susceptible to drought, disease, and invasive species propagation. Their roots systems are weak and they don’t stabilize the entire depth of the vegetative support layer (typically eighteen inches) leaving the layer susceptible to slope slides. Maintaining a non-native grasses based vegetative support layer is expensive. It requires constant mowing, watering, fertilizing and soil addition. Compounding the expense and performance concerns of using non-native grasses is the fact that constant maintenance activities tend to further deteriorate the cap as things like mower ruts lead to water channeling and increased erosion.
With the increased frequency of intense rain events that are happening now in much of the country as a result of climate change, leaving a landfill cap vulnerable to large-scale erosion or even catastrophic slope failure is getting riskier everyday.
And now that it is becoming clear that environmental liability at Subtitle D landfills is extending beyond the anticipated 30-year post closure period, post-closure maintenance expenses have the potential to run in perpetuity. Accounting for the liability of maintenance and the risk of a cap failure needs to reflect this reality — having just one million dollar lawnmower may not be enough!
However, effective landfill cap design can support the responsible party’s goal of reduced liability, including post-closure expenses, through the use of diverse, native plants in lieu of non-native grass. While enhancing the cap to include native plants may slightly increase the capital cost of a cap, it can deliver vast long-term savings in the post closure period that far outweighing the initial additional expenses. The use of native grass, shrubs, bushes and trees represents an attractive alternative to a monoculture of non-native grass.
Designing a vegetative support layer from the beginning to include a more diverse ecosystem has significant environmental and economic benefits. Recognizing that the stewardship of a closed landfill is perpetual, even if the maintenance expenses are not, it clearly makes sense to consider a sustainable, ecologically responsible landfill closure that incorporates an engineered bio-diverse and maintenance free landfill surface.
Effective site design can support the responsible party’s goal of ending active post-closure maintenance and monitoring by more practically achieving zero health risk. While enhancing the cap design does represent near-term cost, it can deliver vast long-term savings by preventing any contaminant exposure without the need to pay for active maintenance and monitoring.