Wastewater Collection Systems  

Updated: 
09-10-2020

Overview

Collection Systems are the system of underground pipes and maintenance structures used to convey wastewater to a Water Resource Recovery Facility (WRRF). In most communities the wastewater collection system is one of the most valuable and largest infrastructure assets. Including gravity sewers, pumping stations, force mains and other sewer conveyance methods, collection systems have brought dramatic improvements to public health. Most sewers carry wastes from households and commercial establishments and are referred to as sanitary sewers. The EPA estimates approximately 500,000 miles of publicly owned sanitary sewers with a similar expanse of privately-owned sewer systems carry wastewater away from homes and businesses to be treated. Whenever possible, gravity (the pipes are placed on a slope so that the water flows with gravity) is used to convey the wastewater, but sometimes pumping stations are used to move the wastewater to higher elevations.

Workers constructing pipeline

Sanitary sewers are sized to carry the amount of sewage generated by the collection area. Sanitary sewers are much smaller than combined sewers designed to also carry surface runoff.

Historically, there were two types of sewer systems: separate sanitary sewer and combined sewer systems (CSS). For separate systems, one set of ditches and pipes carried storm water runoff directly to streams or rivers without treatment, while a different set of pipes carried wastewater to be treated. In combined sewer systems, storm water and sanitary wastes are conveyed in the same pipes. In heavy rain conditions, combined systems can be overwhelmed and discharge untreated waste into receiving waters. Even in separate systems, rainfall can overwhelm collection systems due to inflow (water from downspouts and sump pumps), and infiltration (storm water and ground water entering pipes through cracks and leaky connections). Maintaining collection systems is vital to ensuring safe and effective treatment and compliance with the Clean Water Act.

Workers constructing pipeline

Sanitary sewers are sized to carry the amount of sewage generated by the collection area. Sanitary sewers are much smaller than combined sewers designed to also carry surface runoff.

Description

Sanitary Sewers 
Sanitary sewers (wastewater pipelines) transport wastewater from homes and businesses to a centralized treatment facility. These differ from storm sewers which collect snowmelt and rainwater. Sanitary sewers include pump stations, force mains, manholes, storage facilities, and other components. In the United States, there are approximately 16,000 sanitary sewer systems consisting of over 740,000 miles of public sewer lines.

Sanitary Sewer Rehabilitation  As sanitary sewers age, they can develop defects resulting from aging, structural failures, improper maintenance, or poor design which leads to broken pipes, leaking joints, poorly sealed or hole-filled manhole lids, and root-infested sewers. These defects allow extraneous water infiltration which can overwhelm existing capacity and introduce storm water flows to a wastewater only sewer. Sewer rehabilitation includes repair and renewal as opposed to replacement to extend the useful life of the pipe. There are a variety of options to rehabilitate pipes and many of them are outlined in the above link.

Storm Water  
Storm Water refers to a heavy quantity of water, such as rain or snow, that falls to the surface of the Earth, which becomes polluted as it picks up, carries, and transports various pollutants (oil, grease, chemicals, sediment, nutrients, pathogens) along streets, drains, open channels, and storm sewer systems. Most of the untreated runoff eventually is discharged into nearby waterbodies. However, in combined sewer systems, storm water flows with wastewater and is treated at a water resource recovery facility.

Storm water runoff entering into the local storm drain system

Storm water runoff entering into the local storm drain system.

Inflow and Infiltration 
Rainfall derived infiltration and inflow can overwhelm and impair operation of water resource recovery facilities, causing sanitary sewer overflows and/or basement backups. Utilities can invest in sewer rehabilitation/replacement and work with private property sewer owners to identify sources of infiltration and inflow.

Emerging Issues

Trenchless Technology

Inflow 
To decrease inflow of storm water and groundwater to sanitary sewers, one of the key areas for reduction is private property. To achieve reductions in this area, there are a number of considerations utilities must weigh as they develop a successful framework. Utilities can use voluntary programs (grants, rebates, loans), mandatory programs (selling a house, insurance programs), or combinations of both, and must properly address policy and legal issues by bringing in legal counsel early in the process. As this is an expensive process, proper funding must be secured, whether it is through the private property owners or the utility itself. Lastly, communicating the need for these upgrades to constituents is key to developing support with owners and local officials.

Envision 
Envision aims to provide a consensus-based framework to assess sustainability and resilience in wastewater infrastructure. As a program, it defines the sustainable infrastructure standard, incentivizes programs to go above and beyond minimum requirements, recognizes programs that excel, and has developed a common language for internal and external partners to clearly communicate. Overall, Envision’s framework ensures sustainable choices are made when planning, designing, and constructing infrastructure.

constituents is key to developing support with owners and local officials.

EPA's Wastewater Collection System Toolbox 
This toolbox can be used to identify cost-effective, long-term approaches for communities to manage their aging infrastructure. It provides examples of programs and educational efforts from communities as they communicate with and educate citizens and local officials, address financial and regulatory needs, implement preventative maintenance programs, manage infrastructure assets, and more. The toolbox provides community leaders with a suite of information to better prevent overflows and improve collection systems.

Relevant Codes and Standards

Additional Resources

WBDG

Design Objectives

Cost—Effective, Sustainable: Optimize Energy Use, Protect and Conserve Water