06583 Revised 2008
Copyright © 2008 Regents of the University of Minnesota. All rights reserved.
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A properly designed, installed, operated, and maintained septic system will provide economical and effective sewage treatment. If you properly treat sewage today, future generations will not incur the cost of cleaning up the health or environmental problems that contamination may create.
Many of our daily activities can impact the quality of ground and surface water resources. We must clean the water we use before it can be safely recycled back into the natural environment. Proper handling and treatment of sewage will protect our waters and ourselves from contamination.
Treating sewage is everyone’s responsibility. Residents of towns and cities have their sewage treated at a municipal treatment plant where costs are covered by taxes, assessments, and direct charges. Residents in areas without access to municipal treatment plants own, operate, and maintain their own “mini-treatment plants” – their septic systems.
A septic system may be referred to as an “onsite sewage treatment system,” individual sewage treatment system,” or “wastewater treatment system.” Systems that serve multiple households are often called “cluster systems.” In this Owner’s Guide, septic system will be used to refer to a sewage treatment system not connected to a sanitary sewer.
Sewage is used in this publication to include all toilet (black) water and bathing, dish washing, cleaning, and laundry (gray) water. Another commonly used term for this water is "wastewater."
A septic system is professionally designed to treat sewage for a specific home, business, or group of properties. Proper treatment of sewage recycles water back into the natural environment with reduced health risks to humans and animals and also prevents surface and ground water contamination.
It is unhealthy for humans, pets, and wildlife to drink or come in contact with surface or ground water contaminated with sewage.
Inadequate treatment of sewage allows bacteria, viruses, and other disease-causing pathogens to enter surface and ground water. Hepatitis, dysentery, and other diseases may result from pathogens in drinking water. Disease-causing organisms may make lakes or streams unsafe for recreation. Flies and mosquitoes that are attracted to and breed in wet areas where sewage reaches the surface also may spread disease.
Inadequate treatment of sewage can raise nitrate levels in ground water. High concentrations of nitrate in drinking water can be a special risk to infants, pregnant women, and adults with compromised immune systems. Nitrate affects the ability of blood to carry oxygen; in infants this condition is called methemoglobinemia (blue-baby syndrome). Air quality may also be affected by a septic system; an inadequately vented plumbing system may release odorous or toxic gases into the home.
Figure 1 - Improperly functioning septic system
A septic system that fails to fully treat sewage may allow excess nutrients (phosphorus and nitrogen) to reach nearby lakes and streams, promoting algae and plant growth. Algal blooms and abundant weeds may make lakes unpleasant for swimming, boating, and other water-based activities. This plant growth can also affect water quality for fish and wildlife habitat. As plants die and settle to the bottom, they are broken down by bacteria that use up oxygen that fish need to survive.
Many synthetic cleaning products, pharmaceuticals, and other chemicals used in the house can be toxic to humans, pets, and wildlife. If allowed to enter a septic system, these products may reach ground water, nearby surface water, or the ground surface.
Microorganisms in soil treat wastewater physically,chemically, and biologically before it reaches the ground water, preventing pollution and public health hazards. As septic tank effluent percolates through the soil treatment area, it is purified and in most cases requires no treatment at all before being consumed. However, when the soil is overloaded with water, or when a specific contaminant cannot be treated by the soil, the quality of the underlying ground water may change significantly. Even systems that appear to be working well or were previously permitted because they were thought to provide good treatment may allow nutrients or pathogens to reach surface or ground water. The only way to guarantee effective treatment is to have a trained professional ensure adequate unsaturated and suitable soil exists below the soil treatment area to allow for complete wastewater treatment.
Laurie Brown, Extension Educator, Water Resource Management and Policy and Assistant Professor, University of Minnesota Extension
Sara Christopherson, Extension Specialist, Onsite Sewage Treatment Program and Instructor, Water Resources Center, University of Minnesota Extension
David M. Gustafson, Extension Specialist, Onsite Sewage Treatment Program and Lead Instructor, Water Resources Center, University of Minnesota Extension
Barbara Liukkonen, Extension Educator, Water Resource Management and Policy and Professor, Water Resources Center, University of Minnesota Extension
Nicholas Haig, Program Coordinator, Onsite Sewage Treatment Program, Water Resources Center, University of Minnesota
Doug Malchow, Extension Educator, Water Resource Management and Policy and Assistant Professor, University of Minnesota Extension
Kenneth M. Olson, Extension Educator (retired), Wastewater Treatment Systems and Associate Professor, University of Minnesota Extension
Valerie Prax, Extension Educator, Water Resource Management and Policy and Professor, University of Minnesota Extension
Dan Wheeler, Research Fellow, Onsite Sewage Treatment Program and Instructor
Jessica Wittwer, Program Associate, Onsite Sewage Treatment Program and Instructor
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