Stormwater Dictionary

10 Year Storm Event - a storm that has a 10% probability of occurrence in any given year.

100 Year Storm Event - a storm that has a 1% probability of occurrence in any given year.

2 Year Storm Event - a storm that has a 50% probability of occurrence in any given year.

303(d) waterbody - A list of lakes, rivers, and streams that have been designated as impaired or threatened by a pollutant(s) for which one or more TMDLs are needed. Impaired means that the water is not meeting state water quality standards.

319 - The section of the Clean Water Act that deals with nonpoint pollution

Algal bloom – Rapidly occurring growth and accumulation of algae within a body of water, which usually results from excessive nutrients or sluggish circulation within a waterbody. Persistent and frequent blooms can result in low oxygen conditions which is hazardous to aquatic life.

Aquifer - A geologic stratum containing groundwater that can be withdrawn and used for human purposes.

Average Particle Size - Average size of suspended solids expected to be exported from the site by stormwater runoff.

Backwater - Water upstream from an obstruction which is deeper than it would normally be without the obstruction.

Baffle - A device to deflect, check or regulate flow.  Any deflector device used to change the direction or flow of water.

Base flow – The flow in a stream between storm events. The flow is supplied by groundwater.

Benthic - Relating to or occurring at the bottom of an aquatic ecosystem.

Berm - A constructed barrier of compacted earth.

Best Management Practice (BMP) – actions, behaviors or on-the ground landscaping practices that reduce pollution and/or the amount of storm water runoff flowing into local waterways. BMPs are used to control the generation and delivery of pollutants from the built environment to water ways, thereby reducing the amount of pollutants entering surface and ground waters. BMPs can be structural like stormwater ponds, rain barrels, shoreline buffers or can be non-structural, like street sweeping, picking up after your pet or washing your car on the grass.

Biochemical Oxygen Demand (BOD) – is a measure of the quantity of oxygen used by microorganisms in the oxidation of organic matter.

Biofiltration swale - A long, gently sloped, vegetated ditch designed to filter pollutants from stormwater. Grass is the most common vegetation, but wetland vegetation can be used if the soil is saturated.

Bioretention – A water quality practice that utilizes landscaping and soils to treat stormwater by collecting it in shallow depressions and then filtering it through a planting soil media.

Buffer – (1) A designated area adjacent to and a part of a steep slope or landslide hazard area which protects slope stability, attenuation of surface water flows, and landslide hazards reasonably necessary to minimize risk; or a designated area adjacent to or a part of a stream or wetland that is an integral part of the stream or wetland ecosystem. (2) A vegetated strip immediately adjacent to a water body. The primary function of the buffer is to protect the receiving waterbody from sediment and pollutants derived from upstream areas. (3) An area of trees, shrubs and plants next to a waterbody designed to protect the receiving waterbody from sediment and pollutants contained in storm water runoff. Buffers also function as habitat for migratory birds and aquatic and terrestrial wildlife. (4)  An area of predominantly deeply rooted native vegetated land adjacent to channels, wetlands, lakes or ponds for the purpose of stabilizing banks, reducing contaminants, including sediments, in stormwater that flows to such areas.

Catch basin - Curbside opening that collects rainwater from streets and serves as an entry point to the storm drain system.

Channel - A long, narrow excavation or surface feature that conveys surface water and is open to the air.

Channel, constructed - A channel or ditch constructed to convey surface water; also includes reconstructed natural channels.

Channel, natural - A channel which has occurred naturally due to the flow of surface waters; or a channel that, although originally constructed by human activity, has taken on the appearance of a natural channel including a stable route and biological community.

Clean Water Act - (formerly the Federal Water Pollution Control Act or Federal Water Pollution Control Act Amendments of 1972). Public law 92-500; 33 U.S.C. 1251 et seq.; legislation which provides statutory authority for the NPDES program. Also know as the Federal Water Pollution Control Act. The Clean Water Act prohibits the discharge of any pollutant to waters of the United States from a point source unless the discharge is authorized by a National Pollutant Discharge Elimination System (NPDES) permit.

Check dam - A small barrier built across the direction of water flow in a swale to retain excess water during heavy rains and to slow the speed of runoff traveling through the swale.

Combined sewer system - A system for conveying both sanitary sewage and stormwater runoff.

Constructed conveyance system facilities - Gutters, ditches, pipes, channels, and most flow control and water quality treatment facilities.

Conveyance - The process of water moving from one place to another.

Culvert - Pipe or concrete box structure which drains open channels, swales, or ditches under a roadway or embankment typically with no catch basins or manholes along its length.

Dead storage - The volume available in a depression in the ground below any conveyance system, or surface drainage pathway, or outlet invert elevation that could allow the discharge of surface and storm water runoff.

Depression storage - The amount of precipitation that is trapped in depressions on the surface of the ground.

Detention pond - A facility that collects water from developed areas and releases it at a slower rate than it enters the collection system. The excess of inflow over outflow is temporarily stored in a pond or a vault and is typically released over a few hours or a few days.  A structure designed to temporarily store stormwater runoff for later release in order to delay and reduce peak flow rates. It does not have a permanent pool of water at non storm event times. The most common detention facilities include dry basins.

Discharge - The volume of water (and suspended sediment if surface water) that passes a given location within a given period of time.

Dissolved oxygen (DO) – The amount of oxygen that is dissolved in water. It also refers to a measure of the amount of oxygen available for biochemical activity in a waterbody and as indicator of the quality of that water.

Diversion - A change in the natural discharge location or runoff flows onto or away from an adjacent downstream property.

Domestic wastewater –is wastewater discharged from residences and from commercial, institutional and similar facilities; also known as wastewater or sanitary wastewater.

Drainage - The collection, conveyance, containment, and/or discharge of surface and storm water runoff.

Drainage area or Drainage basin – A watershed. An area draining to a point of interest.  An area of catchment contributing runoff to the treatment system.

Drainage facility - A constructed or engineered feature that collects, conveys, stores or treats surface and storm water runoff. Drainage facilities shall include but not be limited to all constructed or engineered streams, pipelines, channels, ditches, gutters, lakes, wetlands, closed depressions, flow control or water quality treatment facilities, erosion and sedimentation control facilities, and other drainage structures and appurtenances that provide for drainage.

Easement - A right, such as a right-of-way, afforded a person to make limited use of another's real property.

Ecosystem – An interactive system that includes the organisms of a natural community together with their abiotic, physical, chemical and geochemical environment.

Erosion - The process by which the land’s surface is worn away by the action of wind, water, ice or gravity. When land is diminished or worn away due to wind, water, or glacial ice. Often the eroded debris (silt or sediment) becomes a pollutant via stormwater runoff. Erosion occurs naturally but can be intensified by land clearing activities such as farming, development, road-building, and timber harvesting.

ESC - Erosion and Sediment Control

Estuary – Brackish-water area influenced by the tides where the mouth of the river meets the sea.

Eutrophic - A condition of a water body in which excess nutrients, particularly phosphorous, stimulates the growth of aquatic plant life usually resulting in the depletion of dissolved oxygen. Thus, less dissolved oxygen is available to other aquatic life.

Eutrophication - Having waters rich in mineral and organic nutrients that promote a proliferation of plant life, especially algae, which reduces the dissolved oxygen content and often causes the extinction of other organisms. Used for a lake or pond.

Fecal coliform bacteria – Bacteria that are present in the intestines or feces of warm-blooded animals. Often used as indicators of water quality.

First Flush - The first big rain after an extended dry period (usually summer) which flushes out the accumulated pollutants in the storm drain system and carries them straight to the ocean.

Floodplain means that land typically adjacent to a body of water with ground surface elevations at or below the base flood or the 100-year frequency flood elevation and includes detached special flood hazard areas, ponding areas and the like.

Forebay – Stormwater design feature that uses a small basin to settle out incoming sediment delivered in runoff to a stormwater BMP.

Geographic information systems (GIS) – A computer system for capturing, storing, checking, integrating, manipulating, analyzing and displaying data related to positions on the Earth’s surface. Typically, GIS is used for handling maps of one kind or another. These might be represented as several different layers where each layer holds data about a particular kind of feature (i.e., roads, waterbodies, etc). Each feature is linked to a position on the graphical image of a map.

Grading - The cutting and/or filling of the land surface to a desired slope or elevation.

Groundwater - Water below the earth’s surface, often between saturated soil and rock, that feeds drinking wells and springs. Runoff can seep into the soil and recharge groundwater supplies.

Gutter - The edge of a street (below the curb) designed to drain water runoff from streets, driveways, parking lots, etc. into catch basins.

Habitat - The specific area or environment where a plant or animal lives. A habitat must provide all of the basic requirements for life (food, water, shelter) and should be free of harmful contaminants and pollution.

Harmful pollutant - A substance that has adverse effects to an organism including death, chronic poisoning, impaired reproduction, cancer, or other effects.

Household hazardous waste - Common everyday products that people use in and around their homes—including paint, paint thinner, herbicides, and pesticides—that, due to their chemical nature, can be hazardous if not properly disposed

Hydraulics - The science and study of the mechanical behavior of water in physical systems and processes

Hydrologic cycle - The circuit of water movement from the atmosphere to the earth and return to the atmosphere through various stages or processes such as precipitation, interception, runoff, infiltration, percolation, storage, evaporation, and transpiration.

Hydrology- The science of the behavior of water, including its dynamics, composition and distribution in the atmosphere, on the surface of the earth and underground

Illegal Discharge – means any discharge to a MS4 that is not composed entirely of storm water except discharges authorized by a WPDES permit or other discharge not requiring a WPDES permit such as landscape irrigation, individual residential car washing, fire fighting and similar discharges.

Illicit Connection - Any discharge to a municipal separate storm sewer that is not composed entirely of stormwater and is not authorized by an NPDES permit, with some exceptions (e.g., discharges due to fire fighting activities).

Illicit discharges - Discharges of non-stormwater to the storm drainage system. Examples are discharges from internal floor drains, appliances, industrial processes, sinks, and toilets that are connected to the nearby storm drainage system. These discharges should be going to the sanitary sewer system, a holding tank, an on-site process water treatment system, or a septic system.

Impervious surface - A hard surface area which either prevents or retards the entry of water into the soil mantle as under natural conditions prior to development; and/or a hard surface area which causes water to run off the surface in greater quantities or at an increased rate of flow from the flow present under natural conditions prior to development.   Rooftops, sidewalks, parking lots, and street surfaces are examples of impervious surfaces

Infiltration- means the process by which rainfall or surface runoff percolates or penetrates into the underlying soil.

Invert - Elevation to the inside bottom of the pipe.

Maximum Extent Practicable (MEP) - A standard for water quality that applies to all MS4 operators regulated under the NPDES Stormwater Program. Since no precise definition of MEP exists, it allows for maximum flexibility on the part of MS4 operators as they develop and implement their programs.

MS4 or Municipal Separate Storm Sewer System - A conveyance or system of conveyances including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, constructed channels or storm drains, that discharges to waters of the U.S. and is designed or used for collecting or conveying stormwater, is not a combined sewer, and is not part of a publicly-owned treatment works (POTW).

Natural conveyance system elements - Swales and small drainage courses, streams, rivers, lakes, and wetlands.

Natural onsite drainage feature - A natural swale, channel, stream, closed depression, wetland, or lake.

Net Annual TSS Load Reduction - Suspended solids removal efficiency target.

Non-point Source (NPS) pollutants - Pollutants from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even our underground sources of drinking water.

Nonpoint source (NPS) pollution – (1) NPS pollution occurs when rainfall, snowmelt, or irrigation runs over land or through the ground, picks up pollutants, and deposits them into rivers, lakes, and coastal waters or introduces them into ground water. (2) broad term referring to the type of pollution that is caused by non-specific sources, including human-made and natural pollutants. By contrast, the direct dumping of chemicals into a water body by a factory would be a specific source for pollution. (3) Pollution that comes from many different sources in a watershed and is carried by storm water runoff into local waterways. Sources of NPS pollution are difficult to identify and control. Typical NPS pollutants are pet waste, lawn fertilizer, pesticides, car washing detergents, litter and sediment.

Nonstructural BMP - A preventative action to protect receiving water quality that does not require construction. Nonstructural BMPs rely predominantly on behavioral changes in order to be effective. Major categories of non-structural BMPs include education, recycling, maintenance practices and source controls.

NPDES (National Pollutant Discharge Elimination System) – (1) The name of the surface water quality program authorized by Congress as part of the 1987 Clean Water Act. This is EPA's program to control the discharge of pollutants to waters of the United States (see 40 CFR 122.2). (2) A permit issued by the US EPA or a state regulatory agency that sets specific limits on the type and amount of pollutants that a municipality or industry can discharge to a receiving water; it also includes a compliance schedule for achieving those limits. The permit process was established under provisions of the federal Clean Water Act.

NR 151 - created by the WDNR and enacted under NR 216 includes non-agricultural performance standards, agricultural performance standards, transportation performance standards, implementation and enforcement provisions, and a process to develop and distribute non-agricultural technical standards. The non-agricultural performance standards encompass the construction and post-construction phases of new development and redevelopment areas, as well as certain requirements for developed urban areas. The standards targeting a percent removal of the total suspended solids, a reduction of the peak discharge rate, and an increase in the infiltration rate, are intended to protect water quality by minimizing the amount of sediment and other non-point source pollutants that enter waterways.

NR 216  - created by the WDNR and enacted under the WPDES permit establishes criteria defining those storm water discharges needing WPDES storm water discharge permits, as required by s. 283.33, Stats.  The goal of NR 216 is to eliminate to the maximum extent practicable the discharge of pollutants carried by storm water runoff into waters of the state from certain industrial facilities, construction sites and municipal storm water runoff. 

Nutrient – A primary element necessary for the growth of living organisms. For example, nitrogen and phosphorous, are nutrients required for phytoplankton (algae) growth.

Outfall - The point at which storm water is discharged to waters of the state or leaves one municipality and enters another.

Oxygen depletion – Deficit of dissolved oxygen in a water system due to oxidation of organic matter.

Peak Flow - The maximum flow that the collection system is designed to handle, typically associated with a recurrence interval (e.g., 10-yr, 25-yr, 50-y or 100-yr).

Percent Impervious - The specific portion of the contributing drainage area that does not allow stormwater to infiltrate, usually expressed as a percent 0-100%.  Examples include asphalt or bituminous surface and other non-porous or compacted surfaces.

Pervious Surface - A surface that infiltrates rainfall during a large portion of the design rainfall event. Well-managed lawns, fields, and woodlands are examples of pervious surfaces. Pervious materials allow water to soak into the surface by virtue of their porous nature or by “void” spaces in the material.

Phase 1 Stormwater Permit Program - The Phase I program addressed sources of storm water runoff that had the greatest potential to negatively impact water quality. Under Phase I, EPA required NPDES permit coverage for storm water discharges from "medium" and "large" municipal separate storm sewer systems (MS4s) located in incorporated places or counties with populations of 100,000 or more; and eleven categories of industrial activity, one of which is construction activity that disturbs five or more acres of land.

Phase 2 Stormwater Permit Program - The Phase II Program requires NPDES permit coverage for storm water discharges from certain regulated small municipal separate storm sewer systems (MS4s); and construction activity disturbing between 1 and 5 acres of land.

Physically interconnected MS4 - This means that one MS4 is connected to a second MS4 in such a way that it allows for direct discharges into the second system.

Point discharge - The release of collected and/or concentrated surface and storm water runoff from a pipe, culvert, or channel.

Point Source Pollution - Pollution from a single identifiable source such as an industrial factory or a sewage-treatment plant. Most of this pollution s highly regulated at the state and local levels.

Pollutant loading - The total quantity of pollutants in stormwater runoff.

Pollution - Any substance that exists in the environment that is undesirable or harmful for that environment.

Pollution-generating pervious surface - A non-impervious surface with vegetative ground cover subject to use of pesticides and fertilizers. Such surfaces include, but are not limited to, the lawn and landscaped areas of residential or commercial sites, golf courses, parks, and sports fields.

Rain Barrels are often 50 to 80 gallon containers placed underneath downspouts that collect rainwater to reduce runoff volumes discharging offsite. The barrel is often configured with a hose to provide water for gardens and lawns.

Rain Garden - Landscaped areas designed to capture and contain localized runoff. The garden is often planted with plants that can handle wet conditions and have the ability to remove pollutants. A rain garden helps to prevent erosion and reduce stormwater runoff discharging off site.

Reach - A length of channel with uniform characteristics.

Receiving waters – (1) Bodies of water or surface water systems receiving water from upstream man-made or natural systems. (2) Creeks, streams, rivers, lakes, estuaries and other bodies of water into which stormwater flows into.

Recharge - The flow to groundwater from the infiltration of surface and stormwater runoff.

Regulated MS4 - Any MS4 covered by the NPDES Stormwater Program (regulated, small, medium, or large MS4s).

Retention - The process of collecting and holding surface and storm water runoff with no surface outflow.

Retention Pond - A storage structure designed to reduce or eliminate the surface discharge of stormwater through evaporation and infiltration reduce pollutant concentrations.  Wet ponds are the most common type of retention storage.

Riparian - Pertaining to the banks of rivers and streams, and sometimes also wetlands, lakes, or tidewater.

Riprap - A facing layer or protective mound of stones placed to prevent erosion or sloughing of a structure or embankment due to the flow of surface and storm water runoff.

Runoff - Water originating from rainfall and other precipitation that ultimately flows into drainage facilities, rivers, streams, springs, seeps, ponds, lakes, and wetlands as well as shallow groundwater.

Runoff Coefficient - The percentage of rainfall volume that will become runoff.

Runoff means stormwater or precipitation including rain, snow or ice melt or similar water that moves on the land surface via sheet or channelized flow.

Sanitary sewer system - The system that collects and transports sanitary wastewater from building plumbing systems to a wastewater treatment plant for treatment (i.e. wastewater from toilets, showers, sinks, water fountains).

Sediment - Soil or dirt that washes into a body of water and contributes additional nutrients to the water. Sediment often comes from construction sites or bare lawns. Sediment can destroy fish-nesting areas, clog animal habitats, and cloud waters so that sunlight does not reach aquatic plants.

Separate storm sewer - a conveyance or system of conveyances including roads with drainage systems, streets, catch basins, curbs, gutters, ditches, constructed channels or storm drains, which meets all of the following criteria:

Sheet flow - The portion of precipitation that moves initially as overland flow in very shallow depths before eventually reaching a stream channel.

Source control - Action to prevent pollution where it originates.

Storm drainage system - The system built to collect and transport runoff to prevent flooding. This system consists of storm drains, drainage ditches, pipes and culverts. Anything that flows into the storm drainage system flows directly into local creeks and waterways. (Storm water runoff is not treated.) Storm drainage systems are completely separate from those that carry domestic and commercial wastewater (sanitary sewer system).

Storm Sewer - A sewer carrying only runoff from storm events.

Stormwater - Runoff water resulting from precipitation.

Stormwater Facility - all ditches, channels, conduits, bridges, culverts, levees, ponds, natural and manmade impoundments, wetlands, riparian environment, tile, swales, sewers or other natural or artificial structures or measures which serve as a means of draining surface water and groundwater from land.

Stormwater Facility - Facilities that control the discharge of stormwater and that remove pollutants make up the bulk of the structural solutions applied to surface water problems. Stormwater facilities included storage facilities (ponds, vaults, underground tanks, and infiltration systems); water quality facilities (wet ponds, biofiltration swales, constructed wetlands, sand filters, and oil/water separators); and conveyance systems (ditches, pipes, and catch basins). These systems are most often built in conjunction with new development. Once constructed, stormwater facilities require on-going maintenance to ensure they continue to perform as intended. Maintenance of storage facilities typically includes the removal of accumulated sediment and debris, routine mowing, and minor repairs to mechanical appurtenances. Management of water quality facilities is more complex, requiring intensive vegetation management, inspection and maintenance of flow control features, and restoration or replacement of filter media.

Stormwater Management Plan means a document that identifies what actions will be taken to reduce stormwater quantity and pollutant loads from land development activity to levels meeting the purpose and intent of this Section.

Stormwater pollution - Water from rain, irrigation, garden hoses or other activities that picks up pollutants (cigarette butts, trash, automotive fluids, used oil, paint, fertilizers and pesticides, lawn and garden clippings and pet waste) from streets, parking lots, driveways and yards and carries them through the storm drain system and straight to the ocean

Stormwater Pollution is water from rain, irrigation, garden hoses or other activities that picks up pollutants (cigarette butts, trash, automotive fluids, used oil, paint, fertilizers and pesticides, lawn and garden clippings and pet waste) from streets, parking lots, driveways and yards and carries them through the storm drain system to a local water body.

Stormwater Pollution Prevention Plan (SWPPP) - A plan to describe a process whereby a facility thoroughly evaluates potential pollutant sources at a site and selects and implements appropriate measures designed to prevent or control the discharge of pollutants in stormwater runoff.

Stormwater runoff - Water from rain, melted snow or landscaping irrigation that flows over land and into local creeks, streams and waterways. Runoff carries pollutants in it.

Structural BMP - Constructed facilities or measures to help protect receiving water quality and control stormwater quantity. Examples include storage, vegetation, infiltration, and filtration.

Structural Storm Water Management Facilities are engineered and constructed systems that are designed to provide storm water quality control such as wet detention ponds, constructed wetlands, infiltration basins and grassed swales.

Surface water – The water that rests on top of the earth in streams, lakes, rivers, oceans and reservoirs and is open to the atmosphere (i.e. rivers, lakes, creeks, streams, etc).

Swale - A shallow drainage conveyance with relatively gentle side slopes, generally with flow depths less than one foot.

Time of Concentration - The amount of time it takes a drop of water falling in the hydraulically most distant point in the watershed to reach the watershed outfall.

Total Maximum Daily Load (TMDL) - The maximum amount of pollutants which can released into a water body without adversely affecting the water quality.

Toxic - Poisonous, carcinogenic, or otherwise directly harmful to life.

Toxic substances – Those chemical substances, such as pesticides, plastics, heavy metals, detergents, solvents, or any other harmful materials, which are poisonous, carcinogenic, or otherwise directly harmful to human health and the environment.

Tributary - A stream that flows into a larger stream or other body of water.

Turbidity – Having sediment or foreign particles stirred up or suspended in water; muddy.

Urbanized Area (UA) - A Bureau of the Census determination of a central place (or places) and theadjacent densely settled surrounding territory that together have a minimum residential population of 50,000 people and a minimum average density of 1,000 people/square mile. This is a simplified definition of a UA, the full definition is very complex.

Wastewater – Usually refers to effluent from a sewage treatment plant.

Water quality – The biological, chemical and physical conditions of a waterbody; a measure of the ability of a waterbody to support beneficial uses.

Water Quality Criteria - Specific levels of water quality that, if achieved, are expected to render a body of water suitable for its designated use. The criteria are based on specific levels of pollutants that would make the water harmful if used for drinking, swimming, farming, fish production, or industrial processes.

Water Quality Standards - State-adopted and EPA-approved ambient standards for waterbodies. The standards cover the use of the waterbody and the water quality criteria that must be met to protect the designated use or uses.

Water quality treatment facility - A drainage facility designed to reduce pollutants once they are already contained in surface and storm water runoff. Water quality treatment facilities are the structural component of best management practices (BMPs); when used singly or in combination, WQ facilities reduce the potential for contamination of surface and/or ground waters.

Water Tableis the upper limit of a free water surface in a saturated soil or underlying material.

Waters of the State include surface waters, groundwater and wetlands.

Watershed – (1) A geographic area in which water, sediments, and dissolved materials drain to a common outlet, typically a point on a larger stream, a lake, an underlying aquifer, an estuary, or an ocean. A watershed is also sometimes referred to as the "drainage basin" of the receiving waterbody. (2) All land drained by, or contributing water to the same stream, lake, stormwater facility, or draining to a point.

Watershed plan - A plan and all implementing regulations and procedures including but not limited to capital projects, public education activities, land use management regulations adopted by ordinance for managing surface and storm water management facilities, and features within individual subbasins.

Wet Retention Pond - A permanent pool of water with designed dimensions, outlets and storage capacity, constructed to collect, detain, treat and release stormwater runoff.

Wet Volume - The volume available in a depression in the ground below any conveyance system, or surface drainage pathway, or outlet invert elevation that could allow the discharge of surface and storm water runoff.

Wetland - An area inundated or saturated by ground or surface water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas (U.S. Army Corps of Engineers Regulation 33 CFR 328.3 (1988)).

WPDES, Wisconsin Pollution Discharge Elimination System requires municipalities, industrial sites, and animal waste operations discharging water to surface or groundwater to obtain WPDES permits for wastewater discharge, storm water runoff, runoff from large animal operations (CAFOs). Each permit contains monitoring, reporting, and operational requirements needed to ensure pr