May2010_ES&E_2_2010 03/06/10 9:59 PM Page 30
Stormwater Management
Effectively managing stormwater with subsurface infiltration systems By Michelle Zwick
T
hroughout Canada, thousands of stormwater systems are installed in an effort to manage runoff effectively on developed land and prevent pollution of watercourses. Many provinces have instituted stormwater regulations to counteract the potential environmental effects of runoff from impervious surfaces such as roofs and parking lots. For example, Ontario enacted its Clean Water Act in 2006. In Alberta, the Stormwater Management Guidelines document was created in 1987, and updated in 1999, to provide design guidance under the Environmental Protection and Enhancement Act and the Water Act. To manage stormwater, many projects employ certain best management practices (BMPs) to store runoff onsite temporarily and then release it to a municipal system. One particular BMP inPolymaster™ System Now CSA Listed
The POLYMASTER™ liquid polymer mixing/diluting system now complies with both UL778 and CSA C22.2 No. 108-01 standards. The system thoroughly activates emulsion, dispersion and solution polymers, including new high molecular weight liquid polymers, and can produce dilute solution (0.1% – 2.0%) at rates up to 50 gpm. The patented “Gatlin” is a motorized mixing chamber that segments the polymer into ultra-thin film for maximum activation. This system is unique in that the degree of activation is not affected by fluctuating water pressures. Neptune Chemical Pump Co. Lansdale, PA Tel: 888-3NEPTUNE or 215-699-8700 E-Mail: pump@neptune1.com Web: www.neptune1.com
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volves a subsurface retention/detention infiltration and storage chamber system that protects the environment and provides solutions to various provincial and municipal requirements. Stormwater management 101 Containing stormwater can be accomplished with retention and detention systems. Retention is the process for storing stormwater without subsequent surface discharge. In underground retention systems, the chambers capture and hold the stormwater until it is infiltrated back into the ground. While the concept of infiltration is new to many Canadian provinces, it is widely used throughout the United States. In the detention process, runoff is only temporarily stored until it is cast out to an offsite area, such as a storm drain, pond or wetland. A detention system is implemented if a commercial building site does not allow for infiltration practices, because of local municipality regulations or concerns for watershed pollution. Detention systems typically include all of the components of a retention system, along with an impervious liner to prevent the water from being infiltrated and a back-end filter assembly to treat the runoff before it is released into a wetland or storm drain. Controlling stormwater Today’s stormwater BMPs are economical solutions that factor in environmental implications such as water quality and recharge as well as appropriateness for a particular site. These BMPs can be grouped into two broad categories: non-structural and structural. Non-structural BMPs include a range of pollution prevention, educational, institutional, management and development practices, intended to limit the conversion of rainfall to runoff and to prevent pollutants from entering runoff at the source of generation. Structural BMPs deal with stormwater at the point of generation or the point of discharge into the storm sewer system or to receiving waters. They include the following:
• Infiltration systems capture high-volume runoff and infiltrate it into the ground. These systems include underground storage chambers made of highdensity polyethylene, such as Cultec’s Contactor® and Recharger® chambers. • Detention systems capture runoff and temporarily store it until it is released, but do not retain a significant permanent pool of water between snow or rain events. Detention systems are designed to hold the water while infiltration systems are engineered to allow for groundwater recharge. • Retention systems capture runoff and retain it until it is displaced in part or whole by the next runoff event. They maintain a significant permanent pool of water between events. These include wet ponds, retention tanks, tunnels, vaults, plastic chambers, and pipes. • Constructed wetland systems are similar to retention and detention systems, except that vegetation is incorporated, usually at the surface in pond applications, and underwater in meadow-type systems. • Filtration systems use a combination of granular filtering media such as sand, organic material, carbon, or a membrane to remove debris in the runoff. • Vegetated systems (biofilters) such as swales and filter strips are designed to convey or treat shallow runoff and to mimic the functions of a natural forest ecosystem. Advantages of subsurface infiltration systems Subsurface chamber systems can be used in almost any type of stormwater situation. They can serve as subsurface retention or detention systems and as replacements for ponds, concrete structures or pipe and stone installations. They offer many benefits, including: 1. Freeing up space. One of the main benefits of using a subsurface system is the maximum use of land. These systems leave space for additional buildings, parking and landscaping, which is especially important in urban areas where land is at a premium.
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