Alternative Covers
Under Title 27, California Code of Regulations, (27 CCR section 21090), all closed landfills are required to have installed a landfill cap or cover. The landfill cover is intended to maintain a protective seal to keep moisture and rain from penetrating the landfill waste and prevent exposure of the public and the environment to the disposed waste.
The cover must be of a thickness to prevent moisture intrusion into the waste, failure of the cover by erosion and structural or integrity failure, and to prevent the cover from being breached by digging or other activities by wildlife or humans. The cover is intended to protect public health and safety and the environment.
The law requires a prescriptive cover design, one that is established by regulation and intended for use in the closure of all landfills. The prescriptive cover (27 CCR section 21090) shall contain:
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- A foundation layer of not less than 2 feet of appropriate materials.
- Permeability layer not less than 1 foot thick and of hydraulic conductivity not more than 1.0 x 10-6 cm/sec.
- Erosion-resistant layer not less than 1 foot thick capable of sustaining vegetation and resistant to wind, raindrop impact, or runoff or mechanically resistant.
Some design exceptions have been allowed that fall outside the prescriptive standards imposed by the law. These new cover designs can employ plastic high-density polyethylene (HDPE) layers, clay geotextile, and monolithic or mono-covers. The advent of bioreactors is creating another frontier in cover design. The Yolo County Landfill is one instance where a bioreactor is being employed.
Resources
- Evapotranspiration Landfill Cover Systems Fact Sheet: This resource from the U.S. Environmental Protection Agency (EPA) provides current information on final cover design evapotranspiration data.
- Site-Specific Design Report Alternative Cover Demonstration Project-Altamont Sanitary Landfill and Resource Recovery Facility: Site-specific data on mono-cover at the Altamont Landfill, Alameda County.
- Alternative Earthen Final Covers (AEFC) Theory and Practice: A presentation by Bill Albright of the Desert Research Institute, Nevada discusses cover designs.
- Life Cycle Assessment of a Bioreactor and an Engineered Landfill for MSW Treatment: A presentation on a bioreactor lifecycle assessment.