Glossary of Storm Water Terms

Below you will find the definitions for 20 words commonly used in discussing storm water issues. It is not a complete list, but contains many of the more important, and lesser known terms.

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Storm Water - any water that flows during, or following, any form of natural precipitation, and is a result of such precipitation, including snow melt.

Illustration of Denton County Watershed

Luckily, we do not have to worry about snow melt too much around here. But it should be noted that not all storm water is visible. Much of the storm water is flowing under our feet through drainage pipes. All of the storm drains along our streets divert the water somewhere. That is why it is important not to dump harmful chemicals or other substances down storm drains, and to use chemicals on our lawns in moderation. All of the storm drainage eventually finds its way into one of the lakes we all use as a place to play and get our drinking water. The more stuff in our drinking water sources, the more expensive it is to treat the water to make it drinkable, and the higher the cost will be. Those using water wells are not exempt either. If a contaminate makes it way down to the well, it generally has to be abandoned. Depending on how significant the contamination is, a very large area of underground water may become undrinkable.

Watershed - land areas that catch rain or snow and drain to specific marshes, streams, rivers, lakes, or to ground water. 

Various organizations, federal, state and local, depict watersheds differently. The county boundary covers two federally recognized hydrologic units: The Elm Fork of the Trinity and Denton Creek. The hydrologic units are named based on the major river that drains the areas. At the confluence, or meeting, of large rivers, the hydrologic units join to create a new hydrologic unit. This occurs slightly south of Denton County in Dallas County where Denton Creek joins the Elm Fork of the Trinity River. Subsequently, Denton County recognizes four watersheds, one for each of the lakes, and an additional watershed draining the area south of Lake Lewisville and east of Lake Grapevine. A map of the watersheds can be viewed by clicking on the small image in the lower left corner. The watersheds can be further reduced into smaller sub-watersheds that are made up of the areas draining the smaller feeder streams to the major rivers.

Best Management Practices (BMPs) - schedules of activities, prohibitions of practices, maintenance procedures, and other management practices to prevent or reduce the potential for storm water pollution. BMPs also include treatment requirements, operating procedures, and practices to control runoff, spillage or leaks, sludge or waste disposal, or drainage from raw material storage. 

BMPs are not just the control measures implemented to prevent pollution. They also include educating the public to recognize and respond appropriately to improper activities, as well as keeping records and creating useful reports.

Contaminated - containing a harmful quantity of any substance. 

People involved in environmental chemistry have a saying, the dose makes the poison! Meaning too much of anything can be harmful. There have been people who have died from drinking too much water. But for the most part, we are concerned with substances that are harmful in very small quantities, or materials that can be introduced to our waterways in large quantities and result in impaired water quality.

Discharge - addition or introduction of any pollutant, storm water, or any other substance whatsoever into the municipal separate storm sewer system (MS4), into the Waters of the State, or into Waters of the United States.

To many people, a discharge comes from the end of a pipe. But this description is beginning to change. An area of bare of earth, or an area draining a large construction site can discharge pollutants into nearby streams or onto nearby roads. There are measures that can be taken to prevent this from happening. Keeping harmful discharges out of water bodies is one of the goals of the Storm Water Program.

Harmful Quantity - an amount of any substance that will cause pollution of the waters in the State, Waters of the United States, or that will cause sub-lethal adverse effects on representative, sensitive monitoring organisms upon their exposure to samples of any discharge into Waters in the State, Water of the United States, or the MS4.

Like the term contaminated, this varies depending on the substance. Some materials can be added in large quantities, while others are much more toxic and have very low allowable limits, or are not allowed at all!!

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Illicit discharge - a discharge to an MS4 that is not entirely composed of storm water, except authorized discharges identified in the Storm Water Management Programs. 

There are many sources of illicit discharges. Illegal dumping activities lead to illicit discharges, which is one of the reasons reducing illegal dumping is a large part of the storm water program. Oil and grease dumped into storm drains, and other activities of that nature are also considered illicit discharges. It is important to remember that whatever is dumped into storm drains, creeks, streams, lakes, and ditches ends up in our lakes completely untreated.

Major outfall - an outfall that discharges from a single pipe with an inside diameter of 36 inches or more, or its equivalent (discharge from a single conveyance other than a circular pipe which is draining an area greater than 50 acres.) 

Major outfalls represent the points where polluted storm water runoff enters an MS4, or one of our waterways. It is important to remember that it is not a point source, because it represents a large drainage area, as opposed to a pipe coming directly from a facility or building.

Maximum extent practicable - the technology-based discharge standard for MS4s to reduce pollutants in storm water discharges that was established by CWA §402(p). A more detailed discussion of MEP as it pertains to small MS4s can be found at 40 CFR 122.34. 

To the maximum extent practicable allows operators of small MS4s to use means available and easily acquired in order to reduce pollution. This alleviates undo stress on small MS4s. Storm water programs can become expensive, or require more personnel. As a governmental entity with budget constraints, this is not always possible. Therefore, the MS4 operator is allowed to implement those procedures they can, without worrying about large increases in personnel or budget.

Municipal separate storm sewer system (MS4) - the system of conveyances (including sidewalks, roads with drainage systems, County maintained streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains) owned and operated by the County and designed or used for collecting or conveying storm water, and which is not used for collecting or conveying sewage. 

The County is responsible for making sure that water being conveyed through County owned MS4s is not polluted. One way to ensure this does not happen, is to make sure that water flowing into County MS4s is not contaminated. It is important that everyone does their part not to introduce pollution into our waterways.

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National Pollutant Discharge Elimination System (NPDES) - the national program for issuing, modifying, revoking and reissuing, terminating, monitoring and enforcing permits, and imposing and enforcing pretreatment requirements, under sections 307, 402, 318, and 405 of the federal Clean Water Act. 

This is the Federal Regulation that the Storm Water Program is designed to comply with. Texas, as well as many other states, has been given authority from the EPA for where the Texas Commission on Environmental Quality (TCEQ) to monitor compliance through the TPDES. This lessens the burden on the EPA, and places more responsibility on the State agency, which in turn requires local governments to create programs, like the one at Denton County, to ensure the most appropriate BMPs are being used.

Non-point source pollution - any source of any discharge of a pollutant that is not a "point source." 

This is pollution of water as the water flows over the surface of the earth. Sediments, lawn chemicals, soaps, construction debris, improper outdoor chemical storage…; anything that water flowing over the surface can pick up and carry with it on its way to our lakes can become non-point sources of pollution. Non-point source pollution is difficult to manage, because it is often hard to determine the location where the pollution is taking place.

Point source pollution - any discernible, confined, and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, landfill leachate collection system, vessel or other floating craft from which pollutants are or may be discharged. This term does not include return flows from irrigated agriculture or agricultural storm water runoff. 

This is the typical kind of pollution most people are familiar with. However, more stringent regulations have brought decreases in this type of pollution. While these sources of pollution have not been eliminated, they are not as prevalent as they once were.

Pollutant - dredged spoil; solid waste; incinerator residue; sewage; garbage; sewage sludge; filter backwash; munitions; chemical wastes; biological materials; toxic materials; radioactive materials; heat; wrecked or discarded equipment; rock; sand; cellar dirt; and industrial, municipal, recreational, and agricultural waste discharged into water or into the municipal separate storm sewer system. 

A pollutant can be any number of things. While many people think of different chemicals as pollutants, anything that added to the water that causes a change in temperature (up or down), or increases the turbidity (cloudiness), is a pollutant as well. When talking about pollutants, it is always good to remember that a pollutant does not stay where it was released. Rather in the water or in the air, it will move, often to locations many miles away from where it was released.

Pollution - the alteration of the physical, thermal, chemical, or biological quality of, or the contamination of, any Water of the State or Water of the United States, that renders the water harmful, detrimental, or injurious to humans, animal life, vegetation, or property, or to the public health, safety, or welfare, or impairs the usefulness or the public enjoyment of the water for any lawful or reasonable purpose. 

This is the effect on the water of the pollutant. Different types of pollution have different solutions. The best solution of all is prevention!! Trying to fix something after it is broken is always more difficult than preventing the wreck.

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Release - any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into ground-water, subsurface soils, surface soils, the municipal separate storm sewer system (MS4), the Waters of the State, or the Waters of the United States. 

A discharge is a type of release. As you can see, a release just means that a pollutant has been made available to the environment. Many releases are accidental, though there are instances where people have intentionally released harmful substances.

Storm water pollution prevention plan (SWPPP or SWP3) - a plan required by a permit to discharge storm water associated with construction activity, and which describes and ensures the implementation of practices that are to be used to reduce the pollutants in storm water discharges associated with construction activity. 

This is how the regulatory agencies, the County and TCEQ, attempt to ensure the water discharged from construction sites is not harmful to the health of those who will use the lakes for recreation and drinking water sources. The SWPPP will outline the activities to be performed at the construction site, and what mitigation measures will be performed to eliminate or reduce polluting the waters as a result of those activities.

Texas Pollutant Discharge Elimination System (TPDES) - the program created for the State of Texas by TCEQ as agreed upon by the EPA pursuant to 33 USC §1342(b). 

This is the State Regulation that the Storm Water Program is designed to comply with. If the County is found to be in non-compliance, fines and other punitive measures can be enforced until compliance is achieved. Developers involved in construction activities in Denton County must also comply with the TPDES regulations or face fines and the other punitive measures.

Uncontaminated - not containing a harmful quantity of any substance. 

It was once thought that areas where people had not set foot were pristine and uncontaminated. This has been shown to not always be the case. Polar bears have been found to contain pollutants that were never manufactured or used any where near their habitats. Some streams in very remote areas have been found to contain higher levels of some pollutants than streams in the middle of cities. Therefore, the term uncontaminated means just that, there are no harmful quantities of any substance.

Wetland - an area that is inundated or saturated by surface or ground-water at a frequency and duration sufficient to support, and that under normal circumstances does support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas. 

Wetlands are often the some of the most beautiful places to be found. They tend to be habitat for migratory birds, and have an incredibly diverse collection of plants, animals, and insects that make the wetland their permanent home. Aside from this, wetlands perform environmental services no other type of land classification can. They are excellent for filtering water borne pollutants. They also help slow water down, decreasing floods downstream. However, wetlands are very sensitive to how much water enters. If the amount of water is decreased, even a small amount, this could have catastrophic consequences for the wetland.

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