All About Underground Detention Systems

There are many different types of stormwater systems. Many are visible, such as wet ponds, dry detention basins, wetlands, and bio-retention. However, there are many others that are built below ground to accommodate situations where there is limited room for a stormwater system on the surface. These include underground detentions, sand filters, and proprietary devices like Contech StormFilters.

Most underground systems are designed with multiple chambers that each perform a separate function. Sediment chambers are often the first section that stormwater runoff enters. Here, water is held for a period of time to allow sediment and other suspended solids to settle on the chamber floor. The water then may flow into a sand chamber, where the water percolates through layers of sand intended to trap trash, oil, and other contaminants. After filtering through the sand, the water enters a holding chamber from which it slowly drains to an outflow.

Stormwater maintenance is generally performed on a quarterly basis. During a maintenance visit, the technician opens the system and may check to see how much sediment has accumulated, remove trash from each chamber, rake the sand layers to break up any crust or clogs, and ensure the drain orifices are clear so that water can properly flow through and out of the system.

After a period, the sediment accumulated in underground systems will need to be removed. The sand will need to be replaced regularly as well–after a while, it becomes full of the contaminants that it has filtered from the water. Both of these are arduous tasks that require a vacuum truck, so it is recommended that you set aside money each year in anticipation of these repairs. The frequency that they will be needed varies depending on the amount of sediment and pollutants that are introduced to your system.

Each stormwater system is unique and designed to meet the development’s specific needs when controlling runoff. Some systems are huge grids of pipes running under the entirety of a parking lot; others are shallow systems with just a couple of small chambers. Some may have multiple sand or sediment chambers, while others may not have any. It is important to obtain design documents for your property’s underground detention system so that you understand the types and locations of your system’s components.

Contact us today with any questions or to schedule your stormwater maintenance for an underground detention system.

Underground Detention System