A
- Antidegradation (Tier 2, 2.5, 3)
- State or tribal designations for high-quality waters that get extra protection. Under the EPA CGP, sites discharging to them have shorter stabilization deadlines and more frequent inspections.
B
- Best management practice (BMP)
- Any practice, control or procedure used to prevent or reduce stormwater pollution, such as silt fence, mulch, inlet protection or good housekeeping.
- Bioretention
- A shallow, planted depression with engineered soil that captures, filters and often infiltrates runoff. A common low impact development practice.
C
- Catch basin
- A storm drain inlet with a sump below the outlet pipe that traps sediment and debris. See detention vs. retention.
- Check dam
- A small rock, log or fiber barrier placed across a swale or ditch to slow flow and reduce channel erosion.
- Clean Water Act (CWA)
- The federal law that regulates discharges of pollutants into waters of the United States. Section 402 creates the NPDES permit program.
- Common plan of development or sale
- A contiguous area where multiple construction activities may occur at different times under one plan, such as a subdivision. Lots smaller than 1 acre need coverage if the overall plan disturbs 1 acre or more.
- Construction exit (stabilized construction entrance)
- A stabilized pad, usually of aggregate over geotextile, where vehicles leave the site, to reduce sediment track-out.
- Construction General Permit (CGP)
- A general NPDES permit that covers stormwater discharges from construction sites. EPA's 2022 CGP covers areas where EPA is the permitting authority. See lesson 2.
- Corrective action
- Action required when a control needs significant repair or replacement, was never installed or installed wrong, or when discharges violate water quality standards or prohibited discharges occur. See lesson 10.
- Corrective action log
- The record of each corrective action condition and fix. Under the EPA CGP, entries are made within 24 hours of finding and of completing the action.
D
- Detention pond
- A basin that temporarily stores runoff and releases it slowly, draining dry between storms. Mainly controls peak flow.
- Dewatering
- Draining accumulated stormwater or groundwater from foundations, vaults, trenches and similar areas. See dewatering.
- Discharge point
- A location where stormwater leaves the site, such as an outfall, ditch or storm drain inlet.
- Diversion
- A berm, swale or channel that routes water around a disturbed area or to a stable outlet.
E
- Erosion
- Detachment and movement of soil by water, wind or gravity.
- Erosion control
- Practices that keep soil in place, such as vegetation, mulch and blankets. See erosion control BMPs.
- Erosion control blanket (ECB)
- A rolled mat of straw, coconut, wood or synthetic fibers stapled over seeded soil to protect it until vegetation grows. See the blankets guide.
F
- Final stabilization
- Under the EPA CGP, uniform perennial vegetation providing at least 70% of native vegetative cover, or permanent non-vegetative cover, on all disturbed areas not covered by structures.
G
- Good housekeeping
- Practices that keep pollutants out of stormwater, such as covering materials, managing waste, cleaning spills and maintaining equipment.
- Green infrastructure
- Practices that use soil and vegetation to manage stormwater where it falls, such as rain gardens, green roofs and permeable pavement.
H
- Hydromulch (hydroseeding)
- A slurry of seed, mulch fibers, tackifier and water sprayed onto soil to establish vegetation.
I
- Illicit discharge
- Any discharge to a storm sewer that isn't composed entirely of stormwater, except allowed discharges. MS4s must detect and eliminate them.
- Impaired water
- A water body that doesn't meet water quality standards, listed under Clean Water Act section 303(d). Sites discharging to sediment- or nutrient-impaired waters face stricter CGP requirements.
- Impervious surface
- A surface water can't soak into, such as roofs, pavement and compacted gravel.
- Infiltration
- Water soaking into the ground. Infiltration practices reduce runoff volume.
- Inlet protection
- A device or practice that keeps sediment out of storm drain inlets, such as filter bags, curb socks or gravel filters.
L
- Low erosivity waiver (LEW)
- A waiver from construction permit coverage for small sites (1 to under 5 acres) where the rainfall erosivity factor (R) is less than 5 for the construction period.
- Low impact development (LID)
- An approach that manages rain close to where it falls to mimic natural hydrology.
M
- MS4
- Municipal separate storm sewer system: a publicly owned system of conveyances that carries stormwater to waters of the U.S. See lesson 12.
- Mulch
- Straw, wood fiber or other material spread over soil to protect it from raindrop impact and hold moisture.
- Multi-Sector General Permit (MSGP)
- EPA's general NPDES permit for stormwater discharges from industrial facilities.
N
- Natural buffer
- An undisturbed vegetated area between construction and a water body. The EPA CGP calls for a 50-foot buffer or equivalent controls for waters within 50 feet.
- Nephelometric turbidity unit (NTU)
- The unit for turbidity measured with a turbidity meter. The EPA CGP's dewatering benchmark is 50 NTU (weekly average).
- No exposure certification
- A certification that excludes industrial facilities from stormwater permitting when industrial materials and activities aren't exposed to stormwater.
- Notice of Intent (NOI)
- The form an operator submits to obtain coverage under a general permit.
- Notice of Termination (NOT)
- The form an operator submits to end permit coverage, under the EPA CGP within 30 days of meeting a termination condition.
- NPDES
- National Pollutant Discharge Elimination System, the Clean Water Act permit program for point source discharges. See what is NPDES.
O
- Operator
- Under the EPA CGP, a party with control over construction plans and specifications or day-to-day operational control of compliance. Each operator needs coverage.
P
- Perimeter control
- A sediment control along the downslope edges of disturbed areas, such as silt fence or fiber rolls.
- Permeable pavement
- Pavement that lets water pass into a stone reservoir below, such as pervious concrete, porous asphalt or permeable pavers.
- Point source
- A discernible, confined conveyance, such as a pipe, ditch or channel, from which pollutants are discharged.
Q
- QSD / QSP
- California's Qualified SWPPP Developer and Qualified SWPPP Practitioner credentials under the state construction permit. See California training.
- Qualified person (inspector)
- Under the EPA CGP, a person who has completed EPA's construction inspection course and exam, or holds a current certification from a program covering the required topics.
R
- Rational Method
- A formula, Q = CiA, that estimates peak runoff from small drainage areas. See the calculator.
- Receiving water
- A water of the United States into which regulated stormwater discharges.
- Retention pond
- A stormwater basin with a permanent pool of water that provides treatment and peak control.
- Riprap
- Large rock placed to protect channels, slopes and outlets from erosion.
- Runoff coefficient (C)
- The fraction of rainfall that becomes runoff from a surface, used in the Rational Method.
S
- Sediment
- Soil particles carried by water or wind, the main pollutant from construction sites.
- Sediment basin
- A temporary pond that captures runoff so sediment settles. Under the EPA CGP, sized for the 2-year, 24-hour storm or 3,600 cubic feet per acre drained. See the calculator.
- Sediment control
- Practices that capture soil after it moves, such as silt fence, inlet protection and basins. See sediment control BMPs.
- Sediment trap
- A small excavated or bermed area that ponds runoff from a small drainage area so sediment settles.
- Silt fence
- A temporary geotextile fence, buried at the toe, that slows sheet flow so sediment settles. See the silt fence guide.
- Skimmer
- A floating outlet that drains a sediment basin from the water surface, where the cleanest water is.
- Stabilization
- Covering exposed soil with vegetation or non-vegetative materials to prevent erosion.
- Stormwater
- Runoff from rain and snowmelt, including surface runoff and drainage.
- Stormwater team
- The people an operator designates to carry out permit compliance, named in the SWPPP.
- SWPPP
- Stormwater Pollution Prevention Plan, the site-specific plan for complying with a stormwater permit. See what is a SWPPP.
T
- TMDL
- Total maximum daily load: the maximum amount of a pollutant a water body can receive and still meet water quality standards. Permits may include requirements to meet TMDLs.
- Track-out
- Sediment carried off site onto roads by vehicles. Under the EPA CGP, it must be removed by the end of the same business day.
- Turbidity
- Cloudiness of water caused by suspended particles, measured in NTU.
- Turf reinforcement mat (TRM)
- A permanent synthetic mat that reinforces vegetation in channels and high-flow areas.
W
- Waters of the United States
- Waters protected by the Clean Water Act, as defined in federal regulations.
- Wattle (fiber roll)
- A tube of straw, coir or other fiber staked along the contour to slow runoff and trap sediment.
Last reviewed: October 25, 2026 · Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.