Liner Fundamentals: Good Things Start at the Bottom

Corinne, UT 12/15/2017 - Our vision for the Promontory Point Resources landfill is to have a preeminent disposal site that will serve our region at the highest level. We ensure the environmental controls at our disposal sites are kept in strict compliance and pose no damage to the environment. This is why we have continually implemented the best design features with safety as our highest priority.

To understand more about this state-of-the-art disposal site at Promontory Point, we start at the bottom of the landfill itself, which is where we have installed the most advanced protective liner of any landfill in the country.

What is the Liner and Why Do We Need It?

The 2.5 million square feet of liner is composed of eight individual layers and literally protects the bottom of the landfill.

“The purpose of the liner system is to block any potential contaminants from the waste to be introduced to the surrounding environment,” said Caleb Moore, Tetra Tech Division Engineer. “All new landfills in the U.S. require this level of quality, or an equivalent, engineered liner system.

“However, many ‘legacy’ landfills were in place prior to today’s strict federal landfill regulations. In fact, it is rare to have a landfill with all the waste in a lined area like this one.”

To understand its importance, we will describe the function of each layer.

The top layer of the liner consists of an 18-inch-thick processed soil operations layer, which is used to place waste and protect the underlying composite liner. The second layer prevents the top layer from filling in the leachate (waste) collection rock layer.

The third layer consists of 9-inch-thick gravel that collects the precipitation that passes through the overlying leachate.

The fourth layer is a protecting layer that shields the geomembrane layer from the leachate collection layer rock.

Next, a high-density polyethylene liner is rolled out and heat-welded together in large panels.

The sixth layer is a geocomposite clay liner that acts as a redundant secondary layer to prevent liquids from filtering to the groundwater.

The seventh layer is a prepared subgrade layer that has been graded to drain and be smooth, so it does not damage the liner system.

The final and base layer also has a dendritic piping system which collects and removes any liquid that has seeped through the above layers.

“The lining system was initially developed in the 1980s, but today’s systems have continued to improve as research, practical applications and regulations have advanced,” Moore said.

How It’s Made

“The lining system is made up of natural, local, engineered and processed soil resources and carbon-based barrier products,” said Moore. “Environmentally safe, the liner system is, in fact, exponentially safer than some of today’s unlined disposal sites serving the communities in Utah and the United States.”

The high-density polyethylene primary layer has an approximate service life of more than 400 years. Before installation, a rigorous construction quality assurance was performed to ensure contents will not seep into the soil.

Because over 2.5 million square feet of geosynthetics were installed in the liner system, it took approximately three months to install the system, he said.

Extra Aspects

The ideal location for a landfill depends on five key components:

  1. Geological setting;
  2. Relatively arid region;
  3. Distance to the population center, which sets it not too far but not too close;
  4. Regional groundwater; and
  5. Neighboring industries.

Promontory Point Resources’ landfill location also needs to ensure protection of the environment while efficiently serving the people and businesses throughout northern Utah.

Because California-based Tetra Tech designs and constructs tens of millions of square feet of this or similar liner systems every year throughout North America, we selected them as the chief designer of Promontory Point Resources’ landfill.

“Promontory Point Resources is very concerned about ensuring the disposal sites are kept in strict compliance,” Moore said. “This is the reason PPR has continually implemented the best design features to bring a state-of-the-art facility to residents, municipalities and businesses in northern Utah.”