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Abbreviations & Glossary


3RWW – 3 Rivers Wet Weather
ACHD – Allegheny County Health Department
ACO – Administrative Consent Order
ACOE – Army Corps of Engineers
ALCOSAN – Allegheny County Sanitary Authority
BMP- Best Management Practice
CAD – Computer–assisted design
CAP – Corrective Action Plan
CCTV – Closed circuit television
CFR – Code of Federal Regulation
CIPP – Cured-in-place pipe
CMOM – Capacity, Management, Operation and Maintenance
COA – Consent Order and Agreement
CSO – Combined Sewer Overflow
CWA – Clean Water Act
DEP – Department of Environmental Protection
EPA – Environmental Protection Agency
GI- Green Infrastructure
GIS – Geographic Information System
GPS – Global positioning system
I/I – Inflow and infiltration
LID – Low-Impact Development
LTCP – Long–term Wet Weather Control Plan
MBE – Minority Business Enterprise
MDS- Municipal Data Support Site (part of 3RWW web site)
NMC – Nine Minimum Controls (part of the CSO Policy)
NPDES – National Pollutant Discharge Elimination System (permitting program)
POTW – Publicly Owned Treatment Works
PWSA – The Pittsburgh Water and Sewer Authority
SSO – Sanitary Sewer Overflow
WBE – Women’s Business Enterprise
WRDA –Water Resources Development Act


Best Management Practices – Structural (devices installed or constructed) or non-structural (procedures such as modified landscaping practices) control measures taken to mitigate changes to both quantity and quality of urban runoff caused primarily by increased impervious surfaces from land development. BMPs are designed to reduce stormwater volume, peak flows, and/or nonpoint source pollution through evapotranspiration, infiltration, detention, and filtration or biological and chemical actions.

Bioswale - A broad, shallow channel with a dense stand of vegetation covering the side slopes and bottom designed to remove pollution from surface runoff water.

Calibrated Radar Rainfall – a system in which rainfall data from rain gauges is collected and calibrated with radar information from the same time period for a highly accurate rainfall calculation for specific geographic areas.

Cistern – A reservoir or tank for storing rainwater for later use. Used primarily to control runoff from commercial and public facilities.

CMOM (Capacity, Management, Operation & Maintenance) – Also known as the SSO Rule, this proposed regulation sets stringent guidelines for the capacity, management, operation and maintenance of municipal sanitary sewer collection systems.

CSO Policy – Sets short (nine minimum controls) and long-term (long-term control plan) requirements for municipal combined sewer collection systems.

Cleanout – An opening which allows for removing any debris or obstruction that might block the flow of wastewater.

Clean Streams Law – State water quality act regulations. Enforced by the Pennsylvania Department of Environmental Protection, this act is one of the first such environmental laws in the country.

Clean Water Act – A 1977 amendment to the Federal Water Pollution Control Act of 1972, which set the basic structure for regulating discharges of pollutants to waters of the United States. The Act, enforced by the Environmental Protection Agency, prohibits any sanitary sewer overflows and requires that combined sewer overflows be controlled to three or four annually.

Combined Sewer Overflows (CSOs) – When a combined sewer is too full of rainwater and sewage, untreated sewage is discharged through design structures. This is designed to occur during wet weather, but can also occur due to poor operation and maintenance. Overflows also can occur through overflowing manholes or basement backups.

Combined Sewer System – A system that is designed to carry both stormwater and sewage in the same pipe. Combined sewer system communities are regulated by the CSO Policy (Nine minimum controls).

Consent Decree (ALCOSAN) – An agreement between the Allegheny County Sanitary Authority (ALCOSAN) and the United States Environmental Protection Agency (EPA), Pennsylvania Department of Environmental Protection (DEP), and the Allegheny County Health Department (ACHD) for ALCOSAN to achieve compliance with the Clean Water Act during periods of wet weather. The Consent Decree, a binding, legal document that is certified by a federal judge, requires ALCOSAN to meet a series of requirements for planning, design and construction, operation and permitting.

Deep Tunnel System – A system of large pipes buried up to 120 feet under the rivers that are the main conveyance of sewage to ALCOSAN. 

Direct Stream Connections – Creeks and streams in municipalities that are captured in the sewage system and conveyed to ALCOSAN rather than channeled to the river.

Driveway Drain – This drain channels water away from the driveway. On a driveway sloped toward the house, the drain is frequently improperly connected to the sanitary sewer.

Dye Test – A tracer test that is done to determine if downspouts or drains are connected to the sanitary sewer.

Evapotranspiration - A process of transferring water from the earth to the atmosphere by evaporation and plant uptake.

Feasibility Studies – The study and evaluation of alternatives for treating, storing or conveying sewage from communities to the publicly owned treatment plant (ALCOSAN in Allegheny County).

Foundation Drain (also known as a French drain) – A drain installed around a home’s foundation to prevent ground water from entering the basement. Water should be routed to the stormwater system and not the sanitary sewer system.

Green Infrastructure - Management approaches and technologies that infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies.  It’s an approach that helps to store, convey and use rainwater in more natural or nature-like ways.  

Green Roof - the roof of a building that is typically covered with a layer of waterproofing material, then with soil or another planting medium, and planted with grasses, flowers, groundcover, or even shrubs and trees to help manage rooftop runoff.

Heat Island - A metropolitan area which is significantly warmer than its surrounding rural areas due to urban development which uses materials that retain heat.

House Lateral – The pipe that conveys sewage from the house to the public sewer system connection.

Infiltration – When water enters the sewer system through leakage such as a cracked pipe. This can be caused by rainfall or by a high ground water table in the soil.

Inflow – When water enters into the sewer system through an opening such as a manhole lid or roof drain.

Interceptor Sewer – Carries sewage from the trunk sewers to the treatment plant.

Long-Term Wet Weather Control Plan (LTCP) – A detailed plan required under NPDES permits for combined sewer systems. The plan, which includes costly infrastructure projects, must reduce overflows to only three or four wet weather events annually, and must not impact water quality.

Low-Impact Development (LID) - A strategy for controlling urban stormwater runoff that uses land planning and engineering approaches to reduce the impact of new and existing developments through  lot-level techniques, such as green roofs that retain, detain, filter, treat, use, and reduce stormwater runoff. 

Manholes – Structures that are placed at changes in direction and elevations of sewer systems. Manholes are used as access for cleaning the sewer system and other maintenance activities.

Municipal Consent Orders (ALCOSAN service area) - An agreement between the 83 ALCOSAN service area communities and the Pennsylvania Department of Environmental Protection (DEP), and the Allegheny County Health Department (ACHD) for the municipalities to map, assess and repair their sewer systems and to develop a long-term plan for compliance with the Clean Water Act. 

Municipal Satellite Collection System – The portion of the sewer that is owned by the municipality. Excludes the house lateral. Carries sewage from many individual homes to the trunk sewer.

Municipal Separate Storm Sewer Systems (MS4) – A system designed to carry stormwater only. MS4 systems will be regulated by the Stormwater Phase II regulations.

National Pollutant Discharge Elimination System (NPDES) – A national permit system for all discharges to waterways.

Nonpoint Source Pollution - Pollution caused by rainfall or snowmelt moving over and through the ground picking up and carrying away natural and human-made pollutants, depositing them into waterways and/or ground water.

Overflow Structures – Structures that are designed to regulate sewage flows to the treatment plant by discharging excess flows into the rivers.

Porous Pavement – A type of pavement that allows stormwater and snow melt to pass through voids in the paved surface and infiltrate into the sub-base and into the underlying soil.

Pump Station – When a sewage connection cannot be made by gravity, this facility collects the sewage and pumps it to an adjacent sewershed.

Rain Barrel – A barrel connected to a building’s downspout to help capture and control stormwater. The collected water can later be used to water gardens on the property where the barrel sits.

Rain Garden – A specially designed garden that can hold large amounts of rainwater for up to 48 hours, slowly releasing it through the soil or allowing plants to soak it up. 

Rain Gauge - A rain gauge is an instrument that collects and measures rainfall in a specific geographic location. 

Retention Treatment Basin – An artificial lake with vegetation around the perimeter that includes a permanent pool of water in its design to help manage stormwater runoff,  improve water quality in nearby waterways and recharge groundwater. 

Retention or Storage Facility – A tank that is built to store excess wet weather flows from sewer systems to prevent overflows. The tanks are drained back to the treatment plant during dry weather.

Sanitary Sewer System – A system that is designed to carry only sewage. Sanitary sewer system communities will be obligated to meet standards outlined in the new SSO Rule (CMOM) in the very near future.

Sanitary Sewer Overflows (SSOs) – When a sanitary or separate sewer is too full due to inflow and infiltration, untreated sewage is discharged through overflowing manholes and basement backups. This occurs primarily during wet weather, but can also occur due to poor operation and maintenance.

Satellite Treatment Facility – A small wet weather sewage treatment facility located at a point of a combined sewer overflow to treat the sewage before discharging it to streams and rivers.

Sewershed – A defined area whose sewage or stormwater flows to a single point connection at a sewer interceptor pipe or is tributary to a single pump station or treatment plant.

Stormwater Detention Basin - A stormwater management structure consisting of a recessed area of land constructed, or adjacent to, tributaries of rivers, streams or lakes that is designed to regulate the flow of rainwater, and downstream flooding and erosion by storing water for a limited period of a time. Often used in new developments like shopping centers, where the basin remains dry between periods of rainfall.

Stormwater Utility – A utility that charges users a fee based on the contribution of stormwater runoff to the stormwater or sewage collection system. Utility funds the operation, construction and maintenance of stormwater management systems.

Sump pump – A system typically installed in a homeowner’s basement that collects water and pumps it into the stormwater system to avoid wet basements. Sump pumps are frequently illegally connected to the sanitary sewer system. 

Trunk Sewer – Carries sewage from multiple municipal collection systems to the inceptor.

Urban Heat Island Effect - A metropolitan area which is significantly warmer than its surrounding rural areas due to urban development which uses materials that retain heat. 

Vegetated swale - A broad, shallow channel densely planted with a variety of trees, shrubs, and/or grasses designed to attenuate runoff volume from adjacent impervious surfaces, allowing some pollutants to settle out in the process.

Watershed – A region or area bounded peripherally by a divide and draining ultimately to a particular body of water.

Wye – The term for the point of connection between the house lateral and the public sewer.