Landfills have evolved over the last few decades from dumping garbage into any convenient hole in the ground, to a highly complex and technical operation. This includes both the construction of landfills and how they are operated. Modern landfills are engineered and operated, in large part, according to where they are located. Here in the beautiful (and wet!) Northwest, lakes, rivers and streams are abundant and the groundwater table is close to the ground surface. In order to protect these natural resources the modern landfill cell is a highly engineered structure that consists of: 1) a liner 2) the garbage fill 3) a cap 4) a leachate collection system and 5) a gas recovery system.
(Source: The National Energy Education Project, Public Domain)
The liner system is comprised of multiple layers and is over 6 feet thick. It is the barrier system that separates the garbage from the surrounding environment. Click here to see a slideshow of a landfill liner and cap construction sequence. In 2007, Lane County constructed a new landfill liner system for the Phase V cell. This is the current area of the landfill where garbage is being filled. The picture below shows construction of the Phase V liner system.
This portion of the landfill consists of the actual garbage that is brought into the landfill. For more information of how this garbe inflow is handled, see the Landfill Operations page of this site.
A landfill cap is similar to the liner system. It is comprised of multiple layers of soil and geotextiles. Landfills, or portions of landfills, are capped when garbage will no longer be placed in a certain area. The caps are designed and constructed to capture methane gas and reduce stormwater infiltration into the landfill. In 2009, Short Mountain Landfill constructed a final cap on Phase III of the landfill. The photos below shows Phase III during the cap construction.
Spreading clay over drainage geotextile. Rolling liner out over clay layer.
Liner material rolled out over clay layer.
Spreading vegetative soil over liner material.
Leachate Collection System
The leachate collection system is constructed as part of the landfill liner. Leachate is caught on the liner and drains through the gravel layer on top of the liner towards a sump where it is collected. For more detailed information on the leachate system, see the Leachate page of this site.
Gas Recovery System
The gas recovery system is comprised of perforated plastic pipes called wells. The wells convey landfill gas from the landfill to the power generation plant run by EPUD. For more information on the Landfill Gas System at Short Mountain, see the Landfill Gas page of this site.