Tools of the Trade: Safeguarding your sewer system


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It’s not uncommon to hear about a
sewer backup in the news after a heavy
rain. As our wastewater infrastructure
ages and populations continue to grow,
municipalities are increasingly faced with
infrastructure shortcomings. There could be
a number of reasons why sewage backs up
into a basement or a manhole overflows,
spilling raw sewage into a neighborhood
stream. One of the most common is
extraneous storm water and groundwater,
which engineers refer to as infiltration and
inflow (I/I).

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Tools of the Trade: Safeguarding your sewer system

  1. 1. Concepts Fishbeck, Thompson, Carr & Huber, Inc. July 2012Tools of the Trade: Safeguarding Your Sewer SystemIt’s not uncommon to hear about a manholes, sewer mains, or laterals. It can to finding the source and eliminating it.sewer backup in the news after a heavy occur during dry weather when the sewer is Data gathered using various tools providesrain. As our wastewater infrastructure below the groundwater table, or as a result the information necessary to developages and populations continue to grow, of a rainfall event. Inflow describes water cost-effective, short- and long-termmunicipalities are increasingly faced with that gets into the sewers through a direct solutions specific to each community. Theseinfrastructure shortcomings. There could be connection with part of the storm water tools include flow monitoring, hydraulica number of reasons why sewage backs up system, such as a catch basin, yard drain, modeling, field investigations, and theinto a basement or a manhole overflows, or eaves trough. Inflow is usually absent in strategic use of geographic informationspilling raw sewage into a neighborhood dry weather, but after a significant rainfall, system (GIS) One of the most common is it finds its way into the sewers and createsextraneous storm water and groundwater, much higher flow than normal. Sometimeswhich engineers refer to as infiltration and I/I combine and overwhelm a system. Flow Monitoring Installing flow monitors in strategicinflow (I/I). This may lead to water backing up into locations within the sewer system can basements or being discharged into stateInfiltration describes water that seeps into help determine if there is a significant waters, which is classified as a sanitarythe sewers through physical defects in the I/I problem and begin to identify areas sewer overflow. This creates considerable that are contributing the most significant unexpected costs amount of I/I. Flow monitoring also to the state and provides the data necessary to calibrate municipality, and a a hydraulic model of the system. mess no one wants to deal with. Hydraulic Model Locating excess Flow monitoring is a valuable method water sources of acquiring sewer system flow data; and estimating a however, it only provides information particular rainfall’s while the monitors are installed. A properly effects can present calibrated hydraulic model can project a challenge. flows in any storm event and, consequently, Solutions vary test potential solutions for their effect on widely, from the sewer system. For example, would installing larger increasing the sewer’s size eliminate sewers and basement flooding or a sewer overflow? treatment facilities
  2. 2. Funding I/I Studies and Corrections Many funding sources are available and vary from state to state. For example, Michigan has provided grant funding through the State Revolving Fund (SRF) program. S2 Grants, as they are called, pay for 90 percent of the cost of putting together an SRF project plan. These plans typically require all the steps identified here and can be quite economical. FTC&H has prepared several project plans through this program. For more information on how the SRF program works, click here…Field Investigation GIS DataWhen an area is suspected of having potentially If a community has a GIShigh I/I, field investigation techniques can provide populated with system data,a positive means of identifying the specific sources. it can be utilized to isolateA number of techniques can be employed to portions of the system thatidentify various sources. These include smoke have characteristics pointing totesting (filling a sewer with odorless, non- potential I/I problems. Thesestaining smoke and looking for where it escapes characteristics could includethe system), dye testing (adding dye to water pipe age or material, or sectionsat a suspected source to see if it appears in the of sewer in close proximity tosewer), storm cross-connection testing (filling high groundwater conditions ora storm sewer section with dye water to see if water bodies. The GIS data canit appears in the sanitary sewer), or television also serve as the backbone forinspection (inserting a camera in the sewer mains developing a hydraulic document their condition). Inflow Source InfiltraƟon Source Faulty Manhole Roof Drain Cover or Frame ConnecƟon Drainage Uncapped Intake Cleanout Connected Storm Cross- FoundaƟon ConnecƟon Drain Root Intrusion STORM Into Lateral SEWER Faulty Deteriorated Lateral Manhole ConnecƟon Broken SANITARY Cracked or House Lateral SEWER Broken Pipe MAINThese tools can provide a community the information it needs to develop a holistic answerto its I/I problem. Merely identifying and fixing specific problems does not ensure the ratepayers’ money is spent in the most cost-effective manner. Alternative solutions can betested, and their effect on the collection system can be examined and compared to othersolutions and their associated costs. Solutions can vary widely from system to system and For more information regardingare specific to the problem’s characteristics. Sometimes it might make sense to rehabilitate I/I data gathering, please contact:or replace sewer system components, such as pipes or manholes. Other instances mightlead to constructing new facilities, such as retention basins or treatment facilities for Rick Miller, P.E. at (513) 247-8562,overflows. These results should be compared to determine the best possible solution for rcmiller@ftch.comeach problem. Jeff Brown, P.E. at (517) 887-4016,