Mound system
Encyclopedia
A mound system is an alternative to the traditional rural septic system leach field. The mound system is an engineered leaching field used in areas where septic systems are more prone to failure due to having extremely slow or extremely fast permeable soils, soil
with shallow cover over porous bedrock, and soils that have high seasonal water table
The primary waste liquids cleaning and purification action in a leaching field is performed by a biofilm
in the loose fill surrounding the perforated drain tile. If the soil permeability is too low, liquid is not absorbed fast enough, resulting in surface ponding of unsanitary liquids. If the soil permeability is too high, or is exposed fractured bedrock, the wastewater quickly penetrates down to the water table
before the biofilm has time to purify the water, leading to contamination of the aquifer
. In either situation, the mound system provides an ideal habitat for the biofilm and has the correct balance of permeability to assure slow absorption of effluent into the mound before exiting as purified water into the surrounding environment.
, a dosing chamber, and a mound. Waste from homes is sent to the septic tank where the solid fraction settles to the bottom of the tank. The effluent is sent to a second tank called a dosing chamber. In the dosing chamber, the effluent is evenly distributed in doses into the mound. Wastewater is partially treated as it moves through the mound sand. Final treatment and disposal occurs in the soil underneath the mound. The mound system can also better handle the effluent because it doesn't all come into the mound at once allowing the effluent to be better cleaned and helping to keep the mound system from failing.
The absorption mound is built in layers at different depths. The depths of these layers are determined by the depth of the limiting layer of the soil. A limiting layer in soil may be the depth to seasonal water table, depth to bedrock, depth to a fragipan, or depth to glacial till. Each county in Ohio and other states can change the criteria for mounds as they see fit. These are recommended standards that were published by the Ohio State University . These standards state that 24 inches of natural soil should be above the limiting layer in the soil. A layer of specifically sized sand is placed on top of the natural soil. The natural soil and the sand should equal a depth of 4 feet according to Ohio's standards. The distribution pipes that are fed by the dosing chamber are placed on top of the sand in layers of gravel. Then construction fabric and soil are placed on top of the gravel to help keep the pipes from freezing. The top layer of soil also allows the mound to be planted with grass or non-woody plants in order to control erosion
When installing a mound system, the soil in the area where the mound will be placed should not be compacted or disturbed. Any trees that are on the area should be cut away at ground level. The roots and stumps should not be removed. The surface of the area for the mound should then be roughened up with a chisel plow. This prepares the area for the sand. Work should always be done from upslope of the mound area so that the ground down slope of the mound does not get compacted. All mounds are not the same size. Tyler tables are used to help determine the area of a mound.
Time dosing is an important aspect in the functioning of the mound system. According to research done by Darby on sand filters showed that short frequent doses of effluent onto sand filters with orifices that are closely spaced helps to improve effluent quality. This is where time dosing comes into play. Mounds used to be demand dosed and with demand dosed large amounts of effluent are released at once and this passes through the sand very rapidly. This does not give the biota the proper amount of time to clean the effluent .
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
with shallow cover over porous bedrock, and soils that have high seasonal water table
The primary waste liquids cleaning and purification action in a leaching field is performed by a biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...
in the loose fill surrounding the perforated drain tile. If the soil permeability is too low, liquid is not absorbed fast enough, resulting in surface ponding of unsanitary liquids. If the soil permeability is too high, or is exposed fractured bedrock, the wastewater quickly penetrates down to the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
before the biofilm has time to purify the water, leading to contamination of the aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
. In either situation, the mound system provides an ideal habitat for the biofilm and has the correct balance of permeability to assure slow absorption of effluent into the mound before exiting as purified water into the surrounding environment.
History
The mound system was originally designed in the 1940s by the North Dakota College of Agriculture . It was known as the Nodak Disposal System. In 1976 the University of Wisconsin studied the mound systems under the university's Waste Management Project. This project published the first design manual indicating the appropriate site conditions and design criteria for mounds. In 2000 a new manual was released .Design according to Ohio standards
The mound system includes a septic tankSeptic tank
A septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...
, a dosing chamber, and a mound. Waste from homes is sent to the septic tank where the solid fraction settles to the bottom of the tank. The effluent is sent to a second tank called a dosing chamber. In the dosing chamber, the effluent is evenly distributed in doses into the mound. Wastewater is partially treated as it moves through the mound sand. Final treatment and disposal occurs in the soil underneath the mound. The mound system can also better handle the effluent because it doesn't all come into the mound at once allowing the effluent to be better cleaned and helping to keep the mound system from failing.
The absorption mound is built in layers at different depths. The depths of these layers are determined by the depth of the limiting layer of the soil. A limiting layer in soil may be the depth to seasonal water table, depth to bedrock, depth to a fragipan, or depth to glacial till. Each county in Ohio and other states can change the criteria for mounds as they see fit. These are recommended standards that were published by the Ohio State University . These standards state that 24 inches of natural soil should be above the limiting layer in the soil. A layer of specifically sized sand is placed on top of the natural soil. The natural soil and the sand should equal a depth of 4 feet according to Ohio's standards. The distribution pipes that are fed by the dosing chamber are placed on top of the sand in layers of gravel. Then construction fabric and soil are placed on top of the gravel to help keep the pipes from freezing. The top layer of soil also allows the mound to be planted with grass or non-woody plants in order to control erosion
When installing a mound system, the soil in the area where the mound will be placed should not be compacted or disturbed. Any trees that are on the area should be cut away at ground level. The roots and stumps should not be removed. The surface of the area for the mound should then be roughened up with a chisel plow. This prepares the area for the sand. Work should always be done from upslope of the mound area so that the ground down slope of the mound does not get compacted. All mounds are not the same size. Tyler tables are used to help determine the area of a mound.
Time dosing is an important aspect in the functioning of the mound system. According to research done by Darby on sand filters showed that short frequent doses of effluent onto sand filters with orifices that are closely spaced helps to improve effluent quality. This is where time dosing comes into play. Mounds used to be demand dosed and with demand dosed large amounts of effluent are released at once and this passes through the sand very rapidly. This does not give the biota the proper amount of time to clean the effluent .
Additional References
- Solomon, C., P. Casey, C. Mackne, and A. Lake. 1998. Mound Systems. National Small Flows Clearinghouse. 1-2. 10 Oct. 2007. Link.
- National Small Flows Clearinghouse, 1999. MOUNDS: a SEPTIC SYSTEM ALTERNATIVE. Pipeline 10(3): 1-8. Accessed on Oct. 2007. Link.
- SepticAPedia. 2007. Using Septic Mounds as Components of Alternative Septic Systems for Difficult Sites. Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice. 09/05/2007. 15 Oct 2007. Link
- The Water Quality Program Committee. Virginia Tech. 1996. "Maintenance of Mound Septic Systems." Virginia Tech. Virginia Cooperative Extension. Accessed on 15 Oct 2007. Link.
- Mancl, Karen. 1993. Septic Tank - Mound System. Ohio State University Extension. Ohio State University. Accessed on 15 Oct 2007. Link.
- Darby, J, G. Tchobanoglous, M. Arsi Nor, and D. Maciolek. 1996. Shallow intermittent sand filtration: performance evaluation. The Small Flows Journal. 2:3-16.
See also
- BackwaterBackwater (river)A backwater is a part of a river in which there is little or no current. It refers either to a branch of a main river which lies alongside it and then rejoins it or to a body of water in a main river which is backed up by an obstruction such as the tide or a dam.-Alternative channel:If a river has...
- Biofilters (also called a Trickle filter)
- BioreactorBioreactorA bioreactor may refer to any manufactured or engineered device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances derived from such organisms. This...
- CesspitCesspitA cesspit, or cesspool is a pit, conservancy tank, or covered cistern, which can be used to dispose of urine and feces, and more generally of all sewage and refuse. It is a more antiquated solution than a sewer system. Traditionally, it was a deep cylindrical chamber dug into the earth, having...
- Drain-waste-vent systemDrain-waste-vent systemIn modern plumbing, a drain-waste-vent is part of a system that removes sewage and greywater from a building and regulates air pressure in the waste-system pipes, facilitating flow. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped...
- Ecological sanitationEcological sanitationEcological sanitation, also known as ecosan or eco-san, are terms coined to describe a form of sanitation that usually involves urine diversion and the recycling of water and nutrients contained within human wastes back into the local environment....
- Grease interceptorGrease interceptorGrease traps are plumbing devices designed to intercept most greases and solids before they enter a wastewater disposal system. Common wastewater contains small amounts of oils which enter into septic tanks and treatment facilities to form a floating scum layer...
- LatrineLatrineA latrine is a communal facility containing one or more commonly many toilets which may be simple pit toilets or in the case of the United States Armed Forces any toilet including modern flush toilets...
- Composting toiletComposting toiletA composting toilet is a dry toilet that using a predominantly aerobic processing system that treats excreta, typically with no water or small volumes of flush water, via composting or managed aerobic decomposition...
- Mound system (a type of septic system)
- OuthouseOuthouseAn outhouse is a small structure separate from a main building which often contained a simple toilet and may possibly also be used for housing animals and storage.- Terminology :...
- Perc testPerc testA percolation test is a test to determine the absorption rate of soil for a septic drain field or "leach field". The results of a percolation test are required to properly design a septic system...
(Percolation testing for the capacity of soil to absorb water) - Pit toiletPit toiletA pit toilet is a dry toilet system which collects human excrement in a large container and range from a simple slit trench to more elaborate systems with ventilation. They are more often used in rural and wilderness areas as well as in much of the developing world...
- PlumberPlumberA plumber is a tradesperson who specializes in installing and maintaining systems used for potable water, sewage, and drainage in plumbing systems. The term dates from ancient times, and is related to the Latin word for lead, "plumbum." A person engaged in fixing metaphorical "leaks" may also be...
- PlumbingPlumbingPlumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
- Potable cold and hot water supply
- Traps, drains, and ventsPlumbing drainage ventingIn modern plumbing, a drain-waste-vent is part of a system that removes sewage and greywater from a building and regulates air pressure in the waste-system pipes, facilitating flow. Waste is produced at fixtures such as toilets, sinks and showers, and exits the fixtures through a trap, a dipped...
- Rainwater, surface, and subsurface water drainageDrainageDrainage is the natural or artificial removal of surface and sub-surface water from an area. Many agricultural soils need drainage to improve production or to manage water supplies.-Early history:...
- Fuel gas pipingPipingWithin industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid....
- SepsisSepsisSepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
- SeptageSeptageIn the United States, the partially treated waste store in a septic tank is called septage. It generally consists of all the household wastes that are disposed of through a home's plumbing system that neither drain out into the soil nor are converted to gases by the bacteria in the tank.Disposing...
- Sewage treatmentSewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
- SewerSanitary sewerA sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
- Waste disposal
- WastewaterWastewaterWastewater is any water that has been adversely affected in quality by anthropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry, and/or agriculture and can encompass a wide range of potential contaminants and concentrations...