By Don Abresch // 2020-08-10
The Environmental Protection Agency requires every commercial building project to employ certain best management practices (BMPs) to control stormwater and protect water resources. Commercial land development and urban sprawl increase the number of impervious surfaces, such as roofs, paved areas, and sidewalks in the nation’s watersheds, resulting in a greater volume and rate of runoff as well as higher concentrations of pollutants in the runoff.
Riser pipes or curb cuts lead surface storm water to subsurface vaults or systems of large diameter interconnected storage pipes or chambers. Stored water is then released directly through an outlet pipe back into natural waters at rates designed to reduce peak water flows during storms to mimic pre-development conditions.
Underground stormwater storage provides minimal stormwater quality benefits but can be a successful segment to a development’s overall stormwater management plan, when coupled in-line with other stormwater BMPs. The addition of pretreatment features at the system’s inlet can facilitate improvements to water quality by removing floatables, skimming of oils or grease and trap some level of sediments through deposition. Pretreatment is most important if stored water is to be allowed to infiltrate into the soil, otherwise rapid clogging of the system may occur. Pretreatment features can be designed and built into the system or there are commercially available, prefabricated units that can be incorporated within the system during initial planning and design.
As water quality and public health concerns continue to rise, so does the importance of proper stormwater control. Underground storage is most often used in developments where land availability, shape and cost predicate against the development of surface stormwater Best Management Practices.
Because Municipalities typically take over operation and maintenance of underground and surface stormwater treatment structures, through the MS4 Permit, careful attention to design engineering, location, and collaboration with the municipality is paramount.