Can an underground stormwater system be installed in fill?

The process of grading a site requires one of two practices, either cutting or filling. Cutting is the process of excavating material to lower the finished grade from the existing grade, while filling is the process of placing material to bring the existing grade up to the finished grade.

For the purpose of this post, we’re going to focus on the filling process. Soil is placed in the fill and then compacted in order to provide the necessary strength for resisting movement and settling. This process is usually done to create large, flat areas on top with steep, sloped areas along the perimeter to return to existing grade. Although the soil has been compacted, the introduction of water into the fill – especially when we’re talking about the retention of water – leads people to believe that an underground stormwater system cannot be installed.

The introduction of water is a concern because it can reduce the soil cohesion, thereby allowing the soil to move. It can also cause adverse effects like erosion or piping (the process of water following the infrastructure pipes). However, these issues are easily preventable. By enclosing the stormwater management system in an impermeable liner, all seams can be completely sealed off and leaks prevented. It is highly recommended that a manufactured liner constructed of HDPE (high density polyethylene) or PVC (polyvinyl chloride) be utilized to ensure performance. These liners even come with specific components to ensure that connection points are properly sealed to the liners and seepage at the connection is prevented.