lecture 2b soil texture, water & septic tanks drain fields soil texture influences the water content...
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Lecture 2b Soil Texture, Water & Septic Tanks Drain Fields Soil Texture influences the water content of soils. Slide 2 What happens to water when it is added to the soil? Slide 3 Soil Permeability how we describe water movement through the soil Hydraulic Conductivity movement of water through the soil = permeability Determines the suitability of the soil for a septic tank drain field. Slide 4 Permeability Water Transmission Sandy soils will have fast water transmission and low water retention Clay soil will have slow water transmission and high water retention. Slide 5 Porosity and Permeability Porosity is a measure of the open space within soil or rock Pore spaces represent the reservoir for holding water. Permeability is a function of the sizes of particles, pores, and the way they are arranged. Permeability is how quickly water will flow through the soil The straighter and larger the pores, the faster the permeability. Clays tend to reduce the porosity and permeability of soil material due to the small pores. Generally, surface horizons have a larger porosity and subsoils have smaller porosity and reduced permeability Slide 6 Depth to Water Table Many landscapes have soils that are going to be in contact with the water table. Soils will show Wet Soil characteristics when they develop in this type of landscape position. The depth to the water table is independent of soil texture. The soil here will be Saturated when the Water table is high Slide 7 In areas with high water tables - water in the basement or the pit for the basement may occur. Determine the oxidation-reduction status of the soil for clues about this condition. High chroma (bright) well drained soil Low chroma gray, bluish, or gray green anaerobic conditions & high water table is likely A Bg Cg1 Cg2 Slide 8 Basements & Water Tables Water in basement : need to provide drainage tile around the basement next to outer wall, water collected by sump pump in basement Basement gravel Tile Slide 9 New House Construction This condition May eventually lead to a wet basement Slide 10 Sewage Disposal For cities and towns sewage is collected and treated in a waste water treatment plant. The US has spent may billions of dollars upgrading and building these facilities to clean up our surface waters. Some ocean communities still use ocean outfalls for their waste. Slide 11 Septic Tank Systems In rural areas not serviced by sewer systems, a method of disposal of common household and human wastes is necessary. For these areas an anaerobic treatment process called a septic system is employed. Slide 12 Septic Systems The septic system consists of a series of four steps. 1. Septic Tank (collects the wastes from the house) 2. Biological process occurring in the settling tank. (converts solids to liquids) 3. Dosing to the absorption field. (effluent is leaked into the soil from pipes with holes) 4. The absorption field. (soil converts the waste water to clean water) Slide 13 Have you ever been to a place that used a septic tank drain field for sewage waste? How did you know this? Slide 14 Test to determine soil suitability for a septic tank drain field Percolation test : calculate perc rate by measuring time it takes water to drop 1 inch in a pre-wetted hole = time/drop in water level = min/inch see Minnesota Guide to onsite sewage treatment systems for details. http://septic.umn.edu/publications/index.ht ml Slide 15 Soils and the Absorption Field Soil Texture - determines permeability : too slow and field fails, too fast and ground water polluted Depth to water table - less than 3 feet and effluent will pollute groundwater. Depth to bedrock or impermeable layer - water moves laterally on rock and is not cleaned Slope - steep slopes allow effluent to seep out hill side. Soil organisms decontaminate the effluent by killing pathogens. Nutrients absorbed by soil and used by organisms and plants growing on the soil. Slide 16 Septic Systems If the complete septic system is working correctly the homeowner may never have to think where the waste is going. However, major failure of the system could cause major problems and they all fail with age. (20 to 30 years) Too slow percolation will cause the sewage to back up into the house or move over the surface of the soil. Too fast will allow insufficient time for microbes in soil to clean water Slide 17 Septic Systems They system can also fail if the biological organisms are no longer working to metabolize the waste. Detergents and bleaches in sufficient quantity can kill off the organisms. Slide 18 Septic Tank & Wells Slide 19 Leaching Fields Leaching fields contribute Nitrogen to the surrounding soil and eventually water table. As more fields are added to the area, the water tables Nitrate levels increase. This process is faster with soils that have rapid permeability. The Anoka Sand plain is an example of this kind of environmental problem. Slide 20 Alternative Systems Traditional septic systems have proved to be an effective way to treat sewage when space and good soil conditions exist. However -- When space is limited or soil conditions are poor, homeowners may need a modified treatment system. Poor soil conditions include clay textures, soils that are poorly drained, soils shallow to bedrock or soils that are sand and too permeable. Slide 21 Mound System used when soils are not suitable Slide 22 Mound System for Septic tank Drain field Slide 23 Other Alternative Systems a Sand Filter http://www.bae.umn.edu/~septic/LCMR/todd.html http://www.extension.umn.edu/distribution/naturalres ources/DD7672.html The homeowners wanted to try out a new system and maximize their smaller lot by avoiding the use of a mound. A sand filter system was chosen because of its reliability, flexibility, and level profile. A single-pass sand filter system pre-treats septic tank effluent by filtering it through sand before sending it to a soil treatment system. Slide 24 Alternative to septic tank drain fields - flush toilets that dont use water. Slide 25 Compost Toilets Sun Mar & Envirolet A composting toilet must perform 3 completely separate processes 1) compost waste and toilet paper quickly and odorlessly 2) ensure finished compost is safe 3) Evaporate Liquid Slide 26 Composting Units Separating solid wastes from the toilet and delivering them to a composting unit reduces household water use up to 40 percent. Composting removes many pathogens while nutrients are stored in the safe compost which can be used on the garden. Some systems use worms, while others use bacteria and aeration. The composted material must be removed periodically. Cost $1200 -3000 Slide 27