Stormwater Treatment System Satisfies Both Developer and Regulator
Over 30 years have passed since environmental concerns by U.S. citizens resulted in regulations to require the treatment of our municipal sewage and industrial wastes directly discharged into our waterways. Upon implementation of these regulations, such as those under the Clean Water Act of 1972, municipalities and industries believed the cost of complying with these regulations would result in their bankruptcy.
But in 1997, business and the U.S. economy is stronger then ever, and the intentional discharge of sewage, food waste or chemical processing waste to our waterways is unthinkable. Everyone has benefited with an improved quality of life in an environment of cleaner waterways compared to 30 years ago. However, in recent years, studies are indicating we are losing the battle again as the water pollution levels are on the increase. And today the growing source of the pollution is from all of us, and it is more difficult to control than the direct pollution discharge of the past.
The 1992 National Water Quality Inventory Report to Congress concluded that stormwater runoff from a number of diffuse sources including municipal separate storm sewers and urban runoff, known as non-point source pollution, is a leading cause of water quality impairment.
In 1987, The Clean Water Act (CWA) was modified to require implementation of a comprehensive two-phase approach for addressing stormwater discharges under the NPDES program. As a result, Phase I required permits for stormwater discharge from municipalities that serve a population greater than 100,000 and certain industrial activities including departments of transportation, flood control districts, special districts and port authorities. Phase II, to be implemented in 2001, addresses a much broader array of permitees and will be retroactive.
Though the EPA is the governing body of the CWA, much of the implementation and enforcement actions have been delegated to the states and their local jurisdictional authority. Each of these authorities has interpreted the CWA regulations independently and enacted its own stormwater discharge regulations. Accordingly, stormwater Best Management Practices (BMPs) and regulations vary between jurisdictional authorities.
Presently many municipalities require the installation of stormwater BMPs for new commercial and residential developments. To facilitate design by the site engineer these agencies developed BMP design manuals. The majority of the BMPs listed are swales, ponds, and created wetlands. Though in many cases effective, these types of facilities are problematic in that they require large amounts of land and are sensitive to the contributing watershed hydrology. In the urban environment, the cost of constructing these facilities frequently requires a large fraction of the available land or the acquisition of additional land - or they simply are not constructible at all.
Since 1991, Stormwater Management in Portland, Ore., has been developing the CSF® Stormwater Treatment System (CSF®) to address these concerns and provide an economic, high performance treatment system that meets the needs of both the developer and regulator. The CSF has been installed in treating many stormwater runoff situations throughout the United States. These applications include small single retail sites to large urban parking lots, residential streets, urban roadways and freeways. These systems treat stormwater flows from 0.1 to 8 cubic feet per second..
The CSF can be installed in sidewalks and parking lots, and for all practical purposes take up no land space. The CSF also can be installed in challenging application areas with steep slopes and very deep hydraulic grade lines.
The strength of the CSF's effectiveness is in its filter media and design. The development and manufacturing of the filter media begins in the autumn when the deciduous trees begin to drop their leaves. In urban areas the leaves accumulate, clog storm drains, and potentially cause local flooding. To prevent this, many cities have leaf collection programs. Stormwater Management composts deciduous leaves collected by the City of Portland into a mature stable compost. The company then processes the compost into a granular media which has physical and chemical characteristics desirable for the filtration of stormwater.
There are three primary pollutant removal mechanisms performed by the CSF: mechanical filtration to remove sediments, chemical processes to remove soluble metals, and adsorption properties to remove oils and greases (O&G).
Coarse sediments and floatables are removed by pretreatment, and then finer particles are filtered out on surfaces of granules throughout the media matrix. Sediment removal will vary with particle size distribution, but removal has been as high as 95%. Accumulation of sediments is the primary reason for periodic system maintenance.
The media also acts as a chemical filter to remove dissolved ionic pollutants such as heavy metals - including lead, copper, and zinc. Removal rates vary from 65% to 95%.
Removal of oils and greases is facilitated by the media's organic carbon content. The system performs best when O&G loadings are less than 25 mg/l. Measured removal rates are as high as 85%.
The filter media is contained within radial flow filter cartridges housed in pre-cast or cast-in-place vaults to produce a self-contained passive stormwater filtering system. The typical CSF unit consists of an inlet bay, baffle, cartridge bay, an overflow baffle, and outlet bay. Removable radial flow filter cartridges are connected into a pipe manifold cast into the floor of the vault which then discharges to a pipe or waterway. Each cartridge is designed to treat 15 gallons per minute. The cartridges are equipped with a siphon mechanism to greatly enhance their flow potential.
The CSF is designed to be very effective, particularly with those storms early in the rainy season. The CSF's efficiency is highest when pollutant concentrations are highest. Usually based on regulatory requirements, the CSF is sized to treat the peak flow of a water quality design storm.
Stormwater Management is committed to providing efficient systems that minimize the demand for land space while protecting our environment.
James Lenhart, P.E., is the vice president of engineering and research for Stormwater Management. For further information, call 800-548-4667 or visit their website at http://stormwatermgt.com.