Making Sense of Stormwater Quality Management

Raingardens, BMPs, cisterns, catch basins, while the buzzwords are seemingly endless, you may ask yourself, “What is this stormwater quality management thing we keep hearing about?” In layman’s terms, Stormwater Quality Management requirements are regulations established by the Environmental Protection Agency under the authority of the Clean Water Act, to protect and improve stormwater quality as it runs off a particular site and into our nation’s waterways. The EPA delegates this authority to state departments of natural resources and local governments in the form of general permits.

There are many general permits ranging in application from regulating discharges from industrial activities, concentrated animal feeding operations, or municipal storm sewers. For municipal storm sewers, the order requires all Class II cities (cities with populations of 10,000 to 100,000, or cities with populations less than 10,000 but are part of a large metropolitan area) and above, to monitor stormwater quality and implement measures that mitigate the water runoff in their City. Permit holders are responsible for instituting water quality measures that ensure water quality is the same or better as it leaves the site as when it enters. Stormwater quality is primarily controlled by limiting the rate, volume and total suspended solids (TSS) in the stormwater runoff from development sites.

As an example, for new and redevelopment sites in the Kansas City Metropolitan area, this usually means addressing quality issues by choosing design and development techniques that limit TSS discharges to meet a calculated Level of Service (LOS) in water quality. The LOS standard is defined in the Manual of Best Management Practices for Stormwater Quality developed jointly by the Kansas City Metropolitan Chapter of the American Public Works Association and the Mid-America Regional Council. The manual can be downloaded by clicking on the link at the end of this article. Stormwater quality can be managed to meet this LOS through a myriad of techniques often referred to as Best Management Practices or BMPs. These techniques can include both structural and non-structural BMPs that will enhance the stormwater quality prior to the stormwater leaving the site.

A couple of commonly used structural BMPs are raingardens and bio-retention basins. They look like small depressions in the soil with specific, often flowering, plantings that are designed to treat the stormwater runoff from the frequent rainfall events that would otherwise carry the pollutants offsite. Each BMP has a value rating that varies with its ability to remove TSS, reduce runoff volume and temperatures and remove oils and floatables. These BMPs remove pollutants from the stormwater runoff by encouraging infiltration, increasing evapotranspiration, filtering runoff through a select sand/soil medium and by nutrient uptake through the root systems of specially selected native plants. A non-structural BMP may consist of designating an area onsite as “open space” or an area that will not be covered with an impervious surface that will impede infiltration of stormwater. By limiting site disturbance; preserving trees, native vegetation and riparian corridors along streams whenever possible; and by implementing development techniques that limit impervious surfaces, many developments can meet both the required LOS and the needs of the owner.

There are many costs and benefits associated with improving stormwater quality. For private developments, the costs of design and installation of these water quality measures are typically rolled into the development and paid for by the property owner with the benefit of open/green space and environmental quality. Many cities and counties have found the need to implement a stormwater utility fee to cover the expense of meeting the criteria for stormwater quality. A stormwater utility fee is usually an assessment that property owners pay with their water bill each month that helps administer the required monitoring, design and construction of improvements, and maintenance of existing stormwater systems. Ultimately, the costs for improved quality in the nation’s waters are shared through usage fees and services, or costs of goods sold. More importantly, the benefits of improving stormwater quality include improved personal and environmental health, recreation and wildlife habitat.

For more information on Stormwater Quality Management contact:
Jerry Johnson, P.E., LEED AP This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Featured Stormwater Management Projects:
Staley High School – US Green Building Council – LEED Case Study: http://leedcasestudies.usgbc.org/overview.cfm?ProjectID=931

Bell Prairie Elementary School – US Green Building Council Central Plains (formerly Kansas City) Chapter– Certified Projects Website: http://www.usgbckansascity.org/images/stories/project_profiles/bell%20prarieusgbc%20chapter_project_profile.pdf

Look for a future article from SKW regarding the EPA’s newly adopted effluent limits for stormwater runoff from construction sites.

References: APWA/MARC Best Management Practices Manual (August 2009 version): http://kcmetro.apwa.net/chapters/kcmetro/specs/APWA_BMP_ManualAUG09.pdf