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How Do Landfills Work?

Seneca Landfill uses state-of-the-art science and innovative technology to serve our community, protect our environment, and exceed federal standards for the collection and handling of municipal waste.

Seneca Landfill is permitted to accept up to 3,800 tons per day.

Typical Landfill Cross Section

Cross-section of typical landfill at Seneca Landfill in Butler County.

Click to View Full Diagram      Click to View Liner Cross-Section

Bulldozer moving gravel at Seneca Landfill.

Structure of a Landfill

It is important to note the difference between a landfill and a dump. A dump is simply a hole in the ground where trash is buried; dumps are not regulated so they may not be sanitary or well-maintained. Landfills, on the other hand, are a highly complex, well-engineered series of cells in or above the ground. Each cell is lined with an advanced liner system which prevents trash migration and contamination of groundwater. The photo is showing the placement of the protective cover gravel in a newly constructed cell. The structure and make-up of the full liner system is explained below.

Advanced liner system at Seneca Landfill.

Advanced Liner System

After being excavated and brought to grade, each cell is lined with an advanced dual lined containment system consisting of a secondary liner system and a primary liner system for a total of seven (7) layers of protection. The secondary liner system is first placed on the soil subgrade and consists of: a geosynthetic clay liner (GCL), 60-mil high-density polyethylene (HDPE) geomembrane, and a geocomposite drainage layer, used for leak detection. The primary liner system goes on top of the secondary liner system and consists of: a second GCL, a second 60-mil HDPE geomembrane, a 32-ounce non-woven geotextile, and 12-inches of protective cover gravel.

View liner installation slideshow. 

Click here to enlarge the cross-section photo.

Garbage placement at Seneca Landfill.

Garbage Placement

When the new cell is complete, our trucks can start filling it. Each day, garbage disposal companies and trucks hauling waste drive their trucks to Seneca Landfill and either place waste in our lined cells or inside our transfer facility located at the landfill. Waste hauled directly to the landfill cell is unloaded and is immediately spread and compacted with heavy equipment. If waste is unloaded in the transfer station; the trucks unload their trash in the covered building and our site trucks then transfer the waste up to the landfill, where it is disposed into the open cell.

EPA-compliant sedimentation pond at Seneca Landfill.

EPA Compliance and Sustainability

Leachate collection systems and gas collection wells are installed to capture contaminated water and methane gas from the landfill. The water and gas are later treated and purified at our wastewater plant and our gas processing plant (Lego V), respectively. The site ensures compliance with our collection and control systems through a series of groundwater monitoring wells and gas monitoring probes that encapsulate the perimeter of the landfill and are checked quarterly for compliance. In addition to leachate and gas collection controls, the site monitors and controls storm water runoff through a series of collection ditches and sedimentation ponds. As pictured, sedimentation ponds are used to collect and remove sediment from our storm water before it is ever discharged from our site. Our storm water is also tested to ensure compliance with EPA standards.

Geomembrane caps at Seneca Landfill.

Temporary & Permanent Caps

After a landfill cell has been filled, a temporary or permanent cap is installed. A temporary cap is installed on waste that is not at the final permitted grades and where waste from a future adjacent cell construction will overlay these slopes. Permanent caps are installed where the landfill has reached the final permitted grading plan and no additional waste will be placed in these areas. A temporary cap consists solely of a geomembrane liner over a foot of intermediate cover soils. The permanent cap is made up of several layers consisting of a foot of intermediate cover, a geomembrane liner, a geocomposite drainage layer, and two (2) feet of soil cover for drainage and vegetation. At the end of the process, the capped landfill cell looks like a small hill with healthy growing grass.