Landfill Liner Installation Steps

Seneca Landfill takes all possible precautions to ensure our landfill cells are properly designed to protect soil and groundwater. The first step we take is to install a high-density polyethylene (HDPE) geomembrane liner, which is a low-permeability and puncture-resistant material. Liner installation consists of seven layers of protection that ensure our landfill is safe and sanitary. View our slideshow to see the whole process of installing the liner in a new landfill cell.

The slideshow below shows the layers of protection from the bottom up. To view a detail sketch of the liner cross section, click here.

When a new landfill cell is needed, we start by excavating the area. We place a layer of structural fill (compacted soil and rocks) to get the cell to the elevation we require. The difference between our sanitary landfill and an old "dump" is the regulatory requirements to ensure that new cells are fully lined. When we excavate pre-regulatory unlined cells, we first transfer any waste encountered to a lined cell.
This is the raw excavation site of Cell #12 at Seneca Landfill. The picture above depicts the final soil subgrade elevation of the cell, which is the layer under the geosynthetic liner material. This layer is free of any rock or debris, and is smooth enough to prevent punctures to the liner.
The first layer on top of the soil subgrade is the geosynthetic clay liner (GCL). The GCL helps protect the secondary geomembrane layer from the soils. In addition, the GCL is made of bentonite clay that would expand if any punctures or holes were made in the liner.
The next layer is the secondary 60-mil high-density polyethylene (HDPE) geomembrane liner that is rolled out on top of the GCL. The secondary geomembrane is the bottom of the leak-detection zone.
The leak-detection zone consists of a geocomposite drainage layer which is depicted above. The geocomposite consists of two layers of geotextile and a plastic grid that transmits any liquids that would get through the primary geomembrane. As shown above, liners are temporarily held in place with sandbags during installation. Any water detected in this zone is tested to ensure it has not been contaminated. We also do an electric leak detection survey of our liners before placing trash in the cell; if a leak is detected, we find it and fix it.
The picture above depicts workers installing the geocomposite leak detection layer.
Industrial sewing machines are used to sew together the adjacent panels of the geocomposite leak detection layer.
The liner prevents contaminated water called leachate from seeping into the soil or groundwater. Each cell construction is delineated by an inter-cell berm, depicted in the photo to the right.
The next layer is another layer of GCL that goes above the leak-detection layer and under the primary geomembrane.
After the GCL, the primary HDPE geomembrane is installed. This is the fifth layer of the liner system.
The seams for both the primary and the secondary HDPE geomembrane are welded together and pressure-tested for integrity as shown above.
The sixth layer is a thick 32-ounce cushion geotextile that protects the HDPE primary geomembrane from any potential puncture from the final gravel protective cover layer.
The above picture shows the installation of the final layer, a 12-inch gravel protective cover. It helps protect the liner and collects leachate, which is then transmitted to our wastewater treatment plant.
Pipes are installed in the protective cover layer to help transport any leachate to the wastewater treatment plant.
Once the protective gravel layer is installed over the entire cell, the cell is ready to be used. We have a consultant monitor the layers during their installation, and then the cell is inspected and certified by the PA Department of Environmental Protection before use.