United States Solid Waste and CDA/*™ QW 01 n*u
Environmental Protection Emergency Response f; u-«X;
Agency (OS-305) March 1992
Off ice of Solid Waste
Environmental
Fact Sheet
Final Cover Requirements for
Municipal Solid Waste Landfills
Background
On October 9, 1991, the Environmental Protection Agency (ERA)
published final regulations for municipal solid waste landfills. The
regulations address location restrictions, facility design and operations,
ground-water monitoring, corrective action measures, conditions for
closing and providing post-closure care, and financial responsibility
requirements.
In general, all municipal solid waste landfills that are receiving waste on
October 9, 1993 must comply with all of the rule's requirements. However,
any landfill that stops receiving waste between October 9, 1991 and
October 9, 1993, must comply with the federal requirements for the final
cover (as explained in Section 258.60(a) of the final regulations). Cover
requirements are the only ones effective before October 9, 1993. State and
tribal programs may have different closure requirements than the federal
standards. Owners and operators should consult with state and tribal
program officials to ensure they are in proper compliance with all
applicable standards.
Closure Requirements
When an owner/operator stops accepting waste, the owner/operator
must cover the landfill to keep any liquid away from the buried waste. The
purpose of the federal closure requirements is to isolate the waste in a
long-term, low-moisture condition to reduce leachate.
Solid waste landfills must install a final cover within six months of the
last receipt of waste. (States and tribes with EPA-approved permitting
programs may grant extensions to this deadline.) The cover must consist of
-------
an upper erosion layer and a lower infiltration layer designed to minimize
liquids entering the landfill and to prevent erosion. fThe design can vary
when states and tribes have EPA-approved permitting programs.)
The erosion layer consists of a minimum of six inches of earthen
material that protects the infiltration layer and sustains native plant
growth.
The Infiltration layer must be a minimum of 18 inches of earthen
material that has (1) a permeability less than or equal to the permeability of
any bottom liner system or natural subsoils or (2) a permeability no greater
than 1x1 CX5 cm/sec, whichever is less.
However, when a landfill contains a bottom liner system that includes a
flexible membrane or synthetic liner, the infiltration layer must be
composed of a flexible membrane liner and 18 inches of earthen material
with a permeability no greater than IxlO"5 cm/sec. If a landfill does not
contain a flexible membrane or synthetic liner, then the infiltration layer
must be composed of earthen material that is no more permeable than the
recompacted bottom soil liner or natural subsoils. If a landfill has
permeable natural subsoils (greater than IxlO"5 cm/sec), then the final
cover must contain an infiltration layer no greater than 1x10"5 cm/sec.
Considerations in Cover Designs
In addition to complying with the federal regulations governing closure
of municipal solid waste landfills, landfill owners/operators also may want
to address the following issues:
• Does the final cover provide for long-term performance with minimal
maintenance?
• Is the cover properly sloped? (A two-five percent slope is acceptable
after settlement)
• Is the final cover expected to accommodate the effects of settling?
• If a synthetic membrane is necessary as a component of the final
cover, is the props: thickness selected? (A minimum 20 mil synthetic
membrane is generally acceptable.)
• Does the design withstand the effects of freezing and thawing?
• Is the erosion layer thick enough to sustain plant root growth? (More
than six inches of earthen material may be necessary to sustain
proper plant growth.)
• Does the erosion layer contain perennial plants resistant to drought
and temperature extremes?
• Is the erosion layer thick enougfa to protect the infiltration layer from
severe local weather conditions, such as an extended drought?
-------
• Does the infiltration layer need a drainage layer over it to remove any
precipitation that may penetrate the erosion layer?
• Does the cover design include provisions for landfill gas venting?
For More Information
Contact the RCRA Hotline, Monday-Friday, 8:30 a.m. to 7:30 p.m. EST.
The national toll-free number is (800) 424-9346; TDD (800) 553-7672
(hearing impaired); in Washington, D.C., the number is (703) 920-9810,
TDD (703) 486-3323.
Materials related to the municipal solid waste landfill criteria maybe
obtained by writing: RCRA Information Center (RIG), U.S. Environmental
Protection Agency, Office of Solid Waste (OS-305), 401 M Street SW,
Washington, D.C. 20460.
-------
------- |