- • Use pipes to smooth the velocity of the flow of the sewage and not overwhelm the system with turbulence as well as producing excessive amounts of hydrogen sulfide. Piping also reduces corrosion and erosion in the sanitary sewers.
- • See Pump/Lift Stations above for other Best Practices.
Valve, Diversion, and Overflow Structures
• When repairs are made to these structures and the flat surfaces, floors, walls, and roofs have deteriorated and need rebuilding, sealing, or waterproof coating, it is necessary to bind and anchor the new material totally to the structure and have a complete and total waterproof seal applied.
- • Determine the types of defects in the manhole cover, frames, missing or damaged gaskets, etc., and correct them, sealing off potential entry for external water. Replace the manhole cover and frame if necessary and seal it properly.
- • Provide locking lids to keep individuals other than those who are authorized to be in the manhole from entering. This is also very useful to prevent terrorists from planting bombs under the lids.
- • Patch and plug all minor leaks in the manhole structure and use appropriate sealants at all joints and rings internally or externally if accessible.
- • Where the manhole itself is structurally sound, re-seal all joints with waterproof material to prevent excess entry of water into the structure.
- • Depending on the nature of the problem and the cost involved, utilize either chemical grouting, flood grouting spray, or spin coatings and liners including polymer coatings, cured-in-place liners, cast-in-place liners, etc.
- • Establish a strong inspection and maintenance program of all manholes on a regular basis. Combined Sewer Systems
A frequent problem is storm sewers, designed to remove excess water from areas, which use a readily accessible existing system which is also used to transport sanitary sewage away from a community. In 1843, the City of Hamburg, Germany, used the skills of English engineers, combining sanitary sewer discharge with the storm sewer discharge, to make the first combined sewer. Philadelphia is an excellent example of the use of combined sewers. As the city developed in the 19th and 20th centuries, a majority of the streams were diverted into pipes and then the areas were brought up to ground level with fill of millions of yards of dirt. These pipes were then also used for the collection of stormwater runoff and raw sewage from homes as well as wastewater from industries. There was a need to get rid of the sanitary waste because of a sharp increase in the use of water closets. There was also a need to get rid of the wastewater from an ever-expanding industrial economy. Other cities did the same thing. Since, in the United States, many communities had already built storm sewer systems to relieve flooding, it became practical that sanitary sewage wastewater be added to this system. The exception to the combination of the two types of water waste was in Memphis, Tennessee and Pullman, Illinois, where in 1880, engineers separated sanitary waste from runoff into two separate systems. Where wastewater treatment plants were built, they were designed to treat the sanitary sewage and frequently waste from local industries, and not the runoff water. In time of high amounts of rainfall, the sanitary sewerage systems were overwhelmed and the liquid waste had to be diverted to a body of water, thereby contaminating it with raw sewage and chemical and other industrial wastes. Even in properly operating systems, there are times when untreated sewage, stormwater, toxic materials, and industrial waste have to be diverted into surface bodies of water because of unusual volumes which cannot be handled by the treatment plants. This affects swimming, boating, access to beaches, fishing, seafood harvesting, and public drinking water supplies. In 1967, the American Public Works Association conducted a nationwide survey to determine the extent of environmental problems coming from combined sewers, basically found in the Northeast, Great Lakes region, and the Ohio River basin. Over 1300 municipalities and over 36 million people were served by these combined systems; however, the number of industries was not listed. Combined sewers represented about three quarters of all the overflow problems. There was a significant amount of pollution added to surface bodies of water from the raw sewage from people, storm runoff including debris, animal droppings, soil erosion, de-icing compounds, pesticides, PCBs, fertilizers, heavy metals, air pollutant deposits, and industrial waste including hazardous chemicals from factories and other sources. This continues to be a problem today.
After the passage of the Clean Water Act of 1972, numerous new municipal sewerage systems were built and now are approaching the usable time limit for the facilities and pipes. In 2002, the Environmental Protection Agency (EPA) estimated that 23% of sewer pipes were rated as poor, very poor, or no longer acceptable. It is estimated that by the year 2020, 45% of sewer pipes will be in need of immediate repair. It is estimated that 94% of the international market is made up of facilities which need to be refitted or replaced.