The WPWMA operates the Western Regional Sanitary Landfill, located near Highway 65 between Roseville and Lincoln. The current space available, together with recovery efforts by the MRF, will enable the landfill to accept waste well into the 21st century. Here's how the operation works:
Before placing garbage, a liner system is constructed to prevent contamination of the underlying soil and groundwater. The liner system consists of a clay compound and plastic membrane liner, plus a liquid drainage and collection system.
(Click here for larger image)
Refuse is compacted daily to maximize the amount of trash that can be placed in the landfill. This helps to prolong the life of the landfill and reduces the costs of expanding it or building a new one. The compact layers also provide a stable platform for subsequent landfill operations.
Each day, the accumulated garbage is covered with a six-inch layer of "daily cover", which is made from a combination of soil and alternative
daily cover (ADC). The daily cover minimizes landfill odors and prevents
birds, rodents and insects from being attracted to the garbage. The MRF
uses mechanical screening to size-separate materials down to less than a
half-inch in size. This small sized material, referred to as "MRF
fines" are used as "ADC". The MRF fines are comprised of mostly
dirt, grass, and small pieces of plastic and glass. Using the MRF fines
as ADC helps reduce the landfill space taken up by cover soils and
increases the diversion rate, while cutting operational costs.
The decomposing garbage produces methane, an explosive, "greenhouse" gas. The methane gas is collected, which reduces the amount of gas in the atmosphere and protects against potential health hazards. WPWMA has contracted with Energy 2001, who uses most of the gas to generate electricity, which is eventually delivered to the power grid controlled by PG&E. After a recent expansion, the 6 engines operated at the facility are capable of generating enough electricity to power 3,000 homes.
One of three CAT 3156 landfill gas generators at the gas-to-energy plant.
When the landfill reaches maximum capacity, it will be "capped" to prevent liquids from coming into contact with the garbage. The landfill cap mirrors the layered construction of the liner system and includes a top layer of soil to support native grasses, helping the closed landfill to blend in with the natural surroundings.