14 Stormwater Acronyms Every Civil Engineer Should Know

We are an industry of abbreviations and acronyms. The terms we use daily can sometimes hold a general or broad meaning in our minds, but the actual definition of these terms may leave us scratching our heads.  We first blogged about this in 2015, but with so many changes in our industry, we thought it was time to update our list of the top 15 acronyms every engineer should know.

1. BMP - Best Management Practice

Generically, a BMP is considered a best practice or method of addressing a problem such as pollution. The term is widely used to describe stormwater management practices involving structural or engineered control devices and pollution prevention techniques. The term encompasses proprietary devices and traditional designs, such as above-ground retention ponds or riparian areas.

2. CWA - Clean Water Act

Primary federal law in the United States governing water pollution. Its objective is to restore and maintain the chemical, physical, and biological integrity of the nation's waters

3. CSO - Combined Sewer Overflow

Older infrastructure across the nation combined sanitary waste and stormwater runoff in a single conveyance line. Typical operation of the system would carry collected flows to a municipal wastewater treatment facility. During peak storm events, the combined system overflows, or discharges, directly to a body of water. CSO overflows are typically triggered when the volume of runoff exceeds the capacity of the applicable wastewater treatment facility. These systems are no longer standard practice, and the EPA is slowly working with NPDES permit holders to have them removed to eliminate pollutants released to receiving waters during overflow events.

4. LID - Low Impact Development

This site design practice employs stormwater management approaches that help to mimic pre-development hydrology by reducing or eliminating stormwater runoff. An effort is made to manage runoff near the source using smaller integrated stormwater management practices. These solutions include porous paving systems, biofiltration, rainwater harvesting, infiltration systems, green roofs, and filtration systems.

5.  MEP - Maximum Extent Practicable

Stormwater permits require the reduction of pollutants in stormwater discharges to the MEP, including management practices, control measures, & system design & engineering methods.

6. MCM - Minimum Control Measures

Small MS4s are required to implement the 6 MCMs as a condition of their NPDES permit. The 6 MCMs are: 1. Public Involvement and Public Participation. 2. Public Education and Public Outreach. 3. Illicit Discharge Detection and Elimination. 4. Construction Controls. 5. Post-Construction Controls 6. Good Housekeeping.

7. MS4 - Municipal Separate Storm Sewer System

An MS4 is a conveyance system or a system of conveyances, including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains owned by a state, city, town or other public entity that discharges to waterways of the state. These systems are designed to collect and convey stormwater only and are not a combined sewer nor are they part of a publicly owned treatment works facility (sewage treatment plant).

8. NPDES - National Pollutant Discharge Elimination System

As a result of the Clean Water Act, the NPDES program was developed to control the discharge of polluted runoff to the nation's waterways from point and non-point sources, such as pipes or wells and stormwater runoff. The EPA developed the program, but for the majority of the country, the program is administered at the state level.

9. POC - Pollutant of Concern

POC refers to specific pollutants threatening or impairing a particular waterbody. POCs are often hydrocarbons, total suspended solids, nutrients, and metals.

10. SSO - Sanitary Sewer Overflow

An SSO describes an event causing collected sewage to discharge into surrounding water bodies or groundwater sources. Factors contributing to these overflows include line defects, blockages, overload due to stormwater inflow and infiltration, lack of maintenance, or vandalism.

11. SCM -Stormwater Control Measure

Same as BMP.

12. TMDL - Total Maximum Daily Load

The TMDL program was specifically developed to restore impaired waterways. It describes the maximum amount of a pollutant a waterbody can receive and still meet water quality standards. TMDLs are developed for many water quality impairments, including fecal/bacteria, sediment, nutrients (such as Phosphorus and Nitrogen), metals (such as Copper and Zinc), temperature, and pH.

13. TSS - Total Suspended Solids

TSS is currently the most commonly regulated stormwater pollutant. TSS describes the amount of solids suspended/transported in runoff and as a specific analytic method used to measure the concentration of solids in water. Particle sizes and densities vary widely. BMP effectiveness varies from location to location, and designing BMPs for specific performance objectives can be difficult.

14. SWPPP - Stormwater Pollution Prevention Plan (also referred to as SWP3)

SWPPPs are site-specific documents required by Construction & Industrial stormwater permits to:

  • Identify potential sources of stormwater pollution on a construction, industrial &/or municipal site
    Describe stormwater control measures & Best Management Practices (BMPs) that will be used to reduce or eliminate pollutants in stormwater discharges from the project site
    Identify the procedures the operator of the site will implement to comply with the terms & conditions of the permit
    Permits define requirements of the SWPPP