AREA A/B ENGINEERING REPORT - Waste Management

Geosyntec Consultants
along with reduced long-term maintenance requirements that increase wildlife habitat and
other site reuse opportunities.
Under Subtitle D, MSW landfills must use the prescriptive low permeability cover design or an
alternative cover design that meets the performance goals achieved with prescriptive covers. A
typical prescriptive cover system design for a MSW landfill includes, from top to bottom, a sixinch
thick soil vegetative support layer, a geomembrane (GM) upper component of a composite
barrier, and an 18-inch thick compacted clay liner (CCL) lower component of a composite barrier.
A sand or geosynthetic drainage layer (e.g., geocomposite or geonet) is installed above the
barrier layer, or an adequate thickness of cover soil is placed to allow sufficient water storage
for healthy surface vegetation in the overlying soil vegetative support layer. In northern climates,
a greater thickness of soil above the barrier components is necessary to protect the cover system
from freeze-thaw damage. For many final cover systems, the establishment of plant species may
be aided by placing a natural or geosynthetic erosion control (GEC) layer on the surface. Many
cover designs featuring low permeability barrier layers incorporate a landfill gas dissipation
layer (e.g., permeable material) to prevent buildup of gas pressure under the cover system, which
could negatively affect cover components.
Final Cover Systems
Above: Typical Subtitle D prescriptive design.
Right: Equivalent alternative cover all soil
system (i.e., evapotranspirative (ET) design).
Figure 3-3: Final Cover System Design Alternatives
As illustrated on Figure 3-3, the function of a final cover system can also be achieved with
alternative designs, including monolithic soil evapotranspirative (ET) cover systems (e.g., all-soil
MD10186.doc 46 29 March 2009