Underground Sand Filter: Stormwater Control Measure Maintenance

Underground sand filter maintenance requires specialized knowledge and certifications. Dragonfly is here to help!

Kyle Gentry- Division of Operations

Highly urbanized areas can pose two major issues when it comes to stormwater. 1. Increased levels of stormwater runoff and pollutants due to lack of vegetation and primarily impervious surfaces (pavement, rooftops). 2. Lack of surface space to place stormwater control measures.

How do you treat high levels of stormwater runoff when there is not enough surface space to build stormwater control measures? You go underground! Underground stormwater control measures, like an underground sand filter, are ideal for highly urbanized areas. These systems are often built under parking lots.

In an underground sand filter, stormwater will enter the system through an inflow pipe or inlet grates (as pictured above). The water first enters the sedimentation chamber or detention chamber. This chamber acts like a forebay in a pond. It is designed to catch mostly sediment and trash before the stormwater is introduced to the sand filter section. The stormwater filters through the sand to remove pollutants and finer particles. The filtered stormwater is then collected in the underdrains and flows out of the stormwater device.

Like all stormwater control measures, specialized maintenance is critical for the underground system to function as designed. An unmaintained underground sand filter may become clogged with trash and sediment. This can lead to decreased pollutant filtration, flooding, and standing stagnant water that can become a breeding ground for mosquitoes. Upstream construction can lead to clay being washed into the system, which can also clog the sand filter. Maintenance and repairs to underground sand filters require specialized knowledge, certifications, and safety equipment, all of which Dragonfly possesses.

Underground Sand Filter Maintenance Process:

Access to underground sand filters is through manholes or access grates. Grates should be kept clear of trash and debris to help prevent clogs and allow stormwater to flow freely into the system.

Dragonfly’s stormwater management experts remove sediment, trash, and debris from the underground detention chamber. This is the pretreatment area where water is temporarily stored during a storm. From here, the flow is regulated as it progresses to the sand filter chamber.

The crew removes any trash and debris from the underground sand filter. Next, they skim and replace the top layer of compromised sand, roughly 2 inches worth in this case. We typically replace the top layer once a year, otherwise raking may be sufficient maintenance. This allows continued filtration of finer particles and pollutants. After filtering through this chamber, the treated water collects in underdrains where it is then discharged.

Another example of an underground sand filter restored with a fresh top layer of sand.

The stormwater maintenance crew will also inspect all aspects of the underground systems for any issues, such as cracks. In this case, grout was utilized to seal cracks around this outlet pipe. If left unchecked, cracks can continue to worsen and compromise system functionality.

The system is generally maintained by hand. However, sometimes the detention chamber gets too full of muck or sediment and a Vacuum Truck (Vac Truck, pictured above) is required. We see this more often if the system is not maintained or if there is construction upstream.

Construction and major repairs of underground stormwater control measures are more expensive than surface systems. Like all stormwater systems, routine maintenance will help reduce the cost of repairs. Dragonfly’s specialized routine maintenance will save money over the lifetime of the underground system. All of our customized maintenance plans include detailed service reports following every visit. Contact us to learn more about our customized underground stormwater control measure maintenance plans.

Underground Stormwater Maintenance and More!

Learn how Dragonfly will help HOA’s, municipalities, and more stay compliant and within budget. See our innovative solution to improve water quality for this turbid, or muddy, pond.

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Dragonfly Pond Works is a lake, pond, and stormwater management company. We provide stormwater maintenance, stormwater control measure repair, and more throughout North Carolina, in Raleigh, Durham, Charlotte, Cary, and Wilmington. Our pond and lake maintenance services can be found throughout Florida, in Tampa, St. Petersburg, Naples, Sarasota, Fort Myers, and Orlando. We also provide lake and pond maintenance in Myrtle Beach, Charleston, Rock Hill, and Columbia, South Carolina, Atlanta, Athens, and Savannah, Georgia. We strive to develop long-term relationships based on quality work, timely service, cost-efficiency, and of course, trust. Please contact us to learn more.