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Sanitary Sewer Design Wastewater Facilities. But in general, when selecting pipe size and slope, What is a Sanitary Sewer? Most sewer systems are designed to consideration should be given to take advantage of gravity flow. proper estimation of peak design flow. Sanitary sewers, or wastewater pipelines, Therefore, their design depends Pipelines should also support flow transport wastewater from homes and heavily on topography, with sewer velocities that are appropriate for self- businesses to a centralized treatment lines sloping downward toward a cleansing but are not so high as to plant. Along the way, some extraneous wastewater treatment plant at a lower cause pipe damage. Other system water may enter pipelines either from elevation than the tributary system. design considerations include land stormwater or groundwater, a problem use, surface loading, sub-surface In areas with flat terrain, pipes are commonly known as infiltration and inflow conditions and pipe material. buried on a gradient, starting shallow, (I/I). Once wastewater reaches the plant, Commonly used materials include it is treated and returned to the and going deeper until excavation becomes uneconomical. Then, a chloride (PVC) pipe, prestressed environment. Wastewater conveyance concrete cylinder pipes, and ductile or pump or lift station moves wastewater and treatment are important because they cast iron pipes. help to prevent waterborne illnesses and into a new pipe section at the promote general sanitation. minimum burial depth, which is Sanitary Sewer Overflows typically five feet of cover. In areas A properly designed, operated and Sanitary sewers differ from storm sewers, with limited topographic relief or maintained sanitary sewer system is which collect snowmelt and rainwater from places where excavation is meant to collect and convey all of the sidewalks, yards and roadways and route impossible, wastewater may be wastewater that flows into it to a it to nearby surface water. Although conveyed through pressure pipelines wastewater treatment plant. However, stormwater is generally not treated, some (for instance, force mains) by pump or occasional unintentional discharges systems have implemented filtration vacuum. from municipal sanitary sewers – devices to remove certain pollutants. called sanitary sewer overflows Sanitary sewer design is also based (SSOs) – can occur. Overflows can Sanitary sewers also differ from combined on projected flow—the amount of result in sewage flowing into yards, sewers, which transport both stormwater wastewater that will move through the streets or nearby streams as well as in and wastewater to a centralized treatment system based on population, industrial basement backups in which sewage plant. Many older sewer systems in U.S. and commercial contributions, and enters the first floor of a building. city centers consist primarily of combined inflow and infiltration. New sewer sewers but are surrounded by sanitary system design must conform to state During wet weather, infiltration and sewers in newer areas. and local regulations, many of which inflow can cause SSOs when flow follow Recommended Standards for exceeds the maximum system The sanitary sewer system contains capacity. These peak sewer laterals that connect individual wet weather flows can buildings to main sewer pipelines. also cause serious However, sanitary sewers are more than a operating problems at network of pipes. They are an entire wastewater treatment conveyance system that includes pump facilities. In addition, stations, force mains, manholes, storage SSOs can occur during facilities and other components. dry weather due to broken pipes or when According to the U.S. Environmental flow becomes Protection Agency (U.S. EPA), in 2010 obstructed by debris, there were approximately 16,000 sanitary such as grease, roots, sewer systems in the United States with paper products, sand, over 740,000 miles of public sewer lines Crack with infiltration (courtesy of Bergmann, and grit. and 500,000 miles of private lateral Rochester, New York) sewers, serving about 190 million people.

Page | 1 May 2011 CSC052011 property assets, whereas construction use in prioritization, planning and Prevention of SSOs by Design codes do not. User charge rates are renovation of collection systems. frequently adopted as part of SUOs and For simpler systems, engineers have can help assure adequate funding for Inspection techniques range from traditionally used Manning’s equation sanitary sewer systems when rate surface, manhole, and physical entry (steady-state) for designing new and structures are based on equitable inspections to smoke and dye testing to replacement pipes and pump stations. allocation of costs to different classes of technology-based methods involving Using this equation, the system’s customers. Some SUOs also require cameras, lasers or sonar devices. capacity or flow rate is determined by collection systems to set up regular O&M According to the Water Environment cross-sectional area, hydraulic radius, schedules. Operators and sewer Research Foundation, most gravity slope and roughness (friction). For departments establish O&M schedules sewers are 4 to 12 in (10 to 30 cm) in complex systems, it is common to apply through computerized maintenance diameter, and only eight percent are at more sophisticated methods that management systems (CMMS) that track or above 36 in (91 cm), the size many account for dynamic flow behavior. work orders and customer complaints. consider safe for man entry. However, new technologies allow operators to In both cases, computerized programs inspect smaller pipelines and decrease are available through the public or the need for confined space entry. In commercial domain to perform these Key Components of Sewer addition, some technologies can assess calculations. Advances in data Use Ordinances: pipe condition without dewatering, availability, computing power and  Requirements for ownership and saving time and money. analytical software provide engineers establishing sewer service and managers with better tools for  Sewer use restrictions One of the most common inspection planning and designing for capacity and methods is closed-circuit television  Maintenance overflow control. However, regardless of (CCTV), in which a camera is propelled  Inspection and enforcement the tools or equations applied, designers through sewer lines in order to acquire should consider long-term operations  User charges and fees video data and collect information on and maintenance (O&M) concerns.  Private property financing various defects that may occur in the pipe. Sewer scanning and evaluation SSO Regulations technology is similar, providing a CCTV Through the U.S. EPA’s National Operation and Maintenance frontal image along with a 360 degree Pollutant Discharge Elimination System, view of the pipe interior. collection system owners are expected A well designed O&M program with to address SSOs. Although there is no diligent implementation is critical to Laser-based scanning techniques create national regulatory program specific to properly maintaining sewer system a surface profile of the pipe—identifying SSOs, a number of U.S. EPA regions performance. Poor maintenance results defects, debris buildup and more. and state agencies have initiated in system deficiencies, such as Additionally, Ground Penetrating Radar programs to address them. EPA Region blockages and mechanical failures, technologies are available to identify 4’s Management, Operation, and which can cause SSOs. Therefore, voids outside of the pipe, and ultrasonic Maintenance (MOM) Program is one routine inspections are an important part technologies can accurately measure example, along with state programs such of regular O&M. wall thickness and density. Emerging as those in California, Oklahoma, and technologies include omni-directional Wastewater utilities use inspection North Carolina. At this time, the U.S. cameras, acoustic measuring techniques results to develop standardized defect EPA is considering modifications to the and wave impedance probes. coding for manhole and sewer NPDES program concerning SSOs and assets. The National Association of peak flow management. The likely end Sewer Service Companies result of this effort will be changes to (NASSCO) certifies sewer analysts sanitary sewer regulations. under the Pipeline Assessment Sewer Use Ordinances Certification Program (PACP), the Manhole Assessment Certification Sewer Use Ordinances (SUOs), Program (MACP) and the Lateral established by the collection system, Assessment Certification Program supplement building codes in directing (LACP). These programs provide sewer construction, O&M, and usage of the consistency needed to create Self-propelled camera (courtesy of Aries sewer systems. In addition, SUOs comprehensive and reliable data for Industries, Inc., Waukesha, Wisconsin) provide guidance with respect to private

Page | 2 Sanitary System Segmental Improvements sliplining Sewer system improvement programs (courtesy of are established, in general, to meet the Southwest following capacity-related objectives: 1) Pipeline & provide sufficient transport and treatment Trenchless Corp., capacity for existing and future flows Gardena, during both dry- and wet-weather conditions; 2) comply with regulatory requirements for capacity assurance and techniques involve liners, but can also always, owned and maintained by the SSO avoidance; and 3) meet the level of include panel systems and coatings. collection system. Upper laterals run service expected by customers to avoid Finally, replacement can be from this cleanout to the customer’s system surcharging that may lead to accomplished through either home and are typically, but not always, basement or service backups. conventional open-cut or trenchless owned and maintained by the property methods, which are techniques that owner. As infrastructure ages, it becomes more minimize soil disruption. Most trenchless susceptible to deterioration, clogging and techniques use the old pipe as a guide or Many wastewater utilities repair, collapse. Infiltration and inflow also require a carrier pipe. Various trenchless rehabilitate or replace lower laterals. Yet, become progressively worse, methods are listed under pipeline few property owners perform similar contributing to hydraulic overload and replacement and pipeline rehabilitation in maintenance on the upper lateral or even SSOs. Therefore, improvements via the figure below. recognize that it is their responsibility. pipeline rehabilitation and replacement However, private property laterals can techniques are necessary to maintain Lateral Repair, Rehabilitation account for half of I/I entry. Therefore, system performance, renew the life of some wastewater utilities have the system, and address SSOs. and Replacement developed programs to help property Additional conveyance and supplemental Two types of laterals connect sanitary owners address lateral problems. This storage are two more ways of sewer mains to building connections, topic is beyond the scope of this fact addressing SSO problems in particular. upper and lower laterals. Lower laterals sheet, but more information on these connect mains to a cleanout near the programs is available through WEF’s Pipeline and Manhole Repair, property line and are typically, but not Private Property Virtual Library. Rehabilitation and Replacement When a problem is identified in an existing sewer system, usually through one of the inspection methods listed above, pipes must be repaired, rehabilitated or replaced. Point repairs apply to short segments of pipe and allow the pipe to function to the end of its useful life. Repair techniques range from grouting to robotic localized repair to sleeves and liners. In contrast, pipeline rehabilitation can A summary of various trenchless rehabilitation and replacement extend the life of the pipe techniques as well as pipeline repair and manhole rehabilitation and provide structural procedures used at the time this fact sheet was developed. See strength. The most widely WEF Manual of Practice No. FD-6 for more detailed descriptions of used rehabilitation these procedures.

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Citations

WEF Resources U.S. Environmental Protection Agency. "Review of Sewer Design Criteria and RDII Prediction Methods." January Alternative Sewer Systems 2008. EPA/600/R-08/010 MOP FD-12, Second Edition. 2008. U.S. Environmental Protection Agency. ―State of Gravity Sanitary Sewer Design and Construction Technology for Rehabilitation of Wastewater Collection MOP FD-5, 2nd Edition. 2007. Systems.‖ July 2010. EPA/600/R-10/078 Wastewater Collection Systems Management U.S. Environmental Protection Agency. ―Computer Tools MOP 7, 6th Edition. 2008. for Sanitary Sewer System Capacity Analysis and Existing Sewer Evaluation and Rehabilitation Planning.‖ October 2007. EPA/600/R-07/111 MOP FD-6, 3rd Edition. 2009. Great Lakes-Upper Mississippi River Board of State Guide to Managing Peak Wet Weather Flows in Municipal Public Health and Environmental Managers. Wastewater Collection and Treatment Systems. 2006. ―Recommended Standards for Wastewater Facilities.‖ 2004. Private Property Virtual Library www.wef.org/PrivateProperty/ Water Environment Research Foundation. ―An Examination of Innovative Methods Used in the Inspection Prevention and Control of Sewer System Overflows of Wastewater Systems.‖ 2004. MOP FD-17, 3rd Edition. Coming summer 2011.

Perspectives on Collection Systems Rehabilitation and Acknowledgements Replacement – Webcast series. 2010-2011 WEF Collection Systems Committee Collection Systems annual specialty conference Contributing authors William C. Carter, P.E. Vice President, GBA

Chein-Chi Chang, Ph.D., P.E. District of Columbia Water and Sewer Authority

Eric M. Harold, P.E., BCEE Collection Systems Planning Leader, ARCADIS

Luis Roberto León, P.E. Associate, Sr. Project Manager, CDM

Jane McLamarrah, Ph.D., P.E. Vice President, MWH Americas, Inc.

Jimmy Stewart Business Development, Compliance EnviroSystems

Srinivas Vallabhaneni, P.E., BCEE Associate, CDM

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