Tetra Tech’s Mark Swyka, a solid waste senior project manager in the Middletown, New York office, has nearly 40 years of experience in municipal, industrial, and hazardous waste. In this blog, he shares how mechanically stabilized earth (MSE) berms can increase landfill air-space capacity.
I have come to consider mechanically stabilized earth berms as an important addition to the landfill design tool belt. While we continue to refine and optimize recycling and reuse options, the landfill continues as an invaluable resource—too valuable to ignore practical approaches to maximize air-space capacity. In my view, MSE berms offer one such practical approach.
Why consider an MSE berm?
Landfill air space is at a premium. In some circles, landfills get a pretty bad rap. Reputation and/or public perception aside, a well-designed, well-run landfill facility is an important component in the overall materials management strategy—providing secure, low-cost disposal of materials that cannot currently be recycled or repurposed.
With the challenges associated with the permitting and development of new landfill space, the ability to enhance disposal capacity at existing facilities becomes very attractive. The land is already committed to this purpose and extending the facility lifetime just makes sense. And an MSE berm is one way to do this.
Configuration of an MSE berm
Typical MSE berm configuration considers a practical slope of between 3H:1V to 2H:1V facing the waste mass with a steep, near vertical slope on the outside face that reduces the overall quantity of soil required to build the structure.
Is it stable?
The practical slopes and overall height of the MSE berm become a function of the site, the foundation soils, and the materials utilized in the berm construction. Ultimately, the configuration of the berm and the materials of construction will be selected to provide a stable configuration.
How high should a berm be?
The optimal overall berm height—above surrounding grade—can be determined by a comparison of the facility geometry, material usage, cost of construction, and air-space volume gain. From a practical perspective, the optimal berm height is in the range of 30 to 50 feet for small to mid-size landfill facilities and can be higher if circumstances permit. The practical maximum height is probably on the order of 75 feet.
Secure containment of waste materials is paramount. Groundwater and air resources protection, and the general public’s health and welfare is critically important and takes precedence over all other factors. This is why the berm’s lining system must be as protective of the environment as the other containment features of the facility it is incorporated into.
How much benefit can MSE berms offer?
Of course, the benefits of incorporating MSE berms into a site’s design will vary depending on the specific configuration of each site. However, the magnitude of additional airspace that can be created by incorporating MSE berms into site design can be significant. Here are two examples I’ve worked on that show how an MSE berm can add disposal capacity:
For one small to mid-size site, we were able to incorporate a 50-foot high MSE berm around a modest 17 acre lateral expansion. Of the 5,000,000 cubic yards (yd3) of additional disposal capacity, about 2,000,000 yd3 of capacity was directly attributed to the MSE berm.
At a larger facility, the ability to work around a significant footprint allowed the development of a 70-foot high MSE berm around the full perimeter of the existing landfill, as well as a 67 acre lateral expansion. Of the 26,000,000 yd3 disposal capacity provided by this expansion, 15,000,000 yd3 of capacity is directly attributable to the inclusion of the MSE berm.
How much will it cost?
The cost of including MSE berms varies greatly and is directly dependent upon overall facility size and geometry. What we are finding is that the incremental cost of MSE berm design and construction per yd3 of additional air-space capacity generated is generally within the range of about $2.00 to $10.00 per yd3.
Planning for MSE berm implementation
To plan an MSE berm, one must recognize that all berms are not created equal. Even though the final build-out may gain quite a bit of additional air space, one must implement berm inclusion so that construction costs can be distributed across the life of the facility as equitably as possible and are not all incurred up front. This may include constructing specific lengths of berms and/or constructing the berm in incremental heights during the life of the facility.
Have you used MSE berms to increase landfill capacity?