Link
National Association of Flood and Stormwater Management Agencies
As storm water flows over lawns, gardens, sidewalks and streets, it picks up pollutants such as pesticides, pet waste, litter, oil, and soil. Studies by the U.S. Environmental Protection Agency (EPA) and State water pollution control agencies show that storm water runoff is a major source of water pollution, contributing from 50 to 60 percent of the pollutant load in urban water bodies. High density human activities, particularly urbanization, alter water drainage patterns and add pollutants to our rivers, lakes and streams. Polluted water runoff endangers bodies of water being used for drinking, household purposes, recreation and fishing.
What is sediment in storm water?
Sediment is material suspended in water. In the context of urban storm water pollution, sediment is soil carried by storm water into the city's storm drain system and ultimately to a natural body of water such as a stream, lake or bay. Although sedimentation is a natural process, human activity, primarily construction activities in urbanizing areas greatly increases natural sediment loads in water bodies by exposing soil to erosion. Sediment loading rates from construction sites are typically 10 to 20 times greater than pre-construction rates (North Carolina DEHNR, 1993). Over a short period of time, construction sites can contribute more sediment to receiving streams than was naturally deposited over several decades.
Why be concerned about sediment in storm water?
Sediment is the most significant source of urban storm water contamination. By blocking sunlight, sediment inhibits aquatic plant life, and thus harms the fish and shellfish that depend on it. Sediment also interferes directly with aquatic animal life by clogging fish gills and burying insect larvae. Sediment is also a carrier of other forms of pollution, such as toxic chemicals, metals and oils. These pollutants may have built up in the soil of a site for years. When construction on such a site begins, unless erosion is controlled, the contaminated soil is generally carried away by storm water.
How are construction sites involved in storm water pollution?
Construction often involves the creation of large piles of loose soil, and large areas of bare soil that readily erode during rain. The streams of water that form and leave a construction site carry large quantities of sediment. The sediment-loaded water, unless trapped by retention ponds, makes its way to the storm drain system (which is separate from the sewer system in San Diego), and ultimately to local water bodies. Pollutants such as petroleum products, chemicals from construction materials, and metals are often present in the soil or are added to the site during construction. These pollutants attach to soil particles move off the site with storm water.
Are efforts made to control storm water pollution from construction sites?
In the San Diego region, discharges of runoff from construction sites are subject to both federal, state and local regulation. The statutes currently in force are:
- Federal
Clean Water Act (CWA)
The federal Clean Water Act of 1972 and amendments in 1987 established certain water pollution control regulations and permit requirements. This program is called the National Pollutant Discharge Elimination System (NPDES). Sediment runoff rates from construction sites "greatly exceed natural erosion rates of undisturbed lands causing siltation and impairment of receiving waters."
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California Regional Water Quality Control Board, Storm Water Permit, San Diego
Region, Order No. 2001- 01
Order 2001-01 requires that the City maintain a "watershed based inventory of all construction sites within its jurisdiction regardless of site size or ownership." (p.23, Order No. 2001-01)
Construction site contractors are required to implement Best Management Practices (BMPs) to reduce pollutants to storm water runoff. BMPs can generally be considered all practices that are employed to reduced storm water pollution including, including both structural and non-structural measures such as:
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Erosion prevention and slope stabilization; click here to see soil roughening, fiber rolls, and fiber matrix covering
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Revegetation: click here to see example of hydromulching
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Retention of sediment and other construction pollutants on site: click here to see gravel bags, silt fences, and fiber rolls
Detailed information on specific guidance to implement BMPs, please refer to Construction Best Management Practices, and to the EPA Study on BMPs to control urban storm water pollution.
- San Diego County Storm Water Ordinance (No. 8394)
The County Storm Water Ordinance (No. 8394) addresses the management and discharge of pollutants to the County’s Storm Water Conveyance System (street gutters, storm drains, drainage ditches, etc.) and receiving waters (oceans, creeks, rivers, estuaries, etc). Construction site owners and developers are responsible for keeping storm drains and other discharge points (drainage channels, sheet flow areas, etc.) clear throughout the entire construction site, including perimeter areas where surface runoff exits the site.
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Send mail to yli@rohan.sdsu.edu with questions or comments about this web site.
Copyright © 2002 Construction Site Storm Water Monitor (g596 group project)
Last modified: 05/09/02