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What is LTAR ?
The long-term acceptance rate (LTAR) is the amount of wastewater that can be applied each day over an indefinite period of time to a square foot of soil. Effluent from the onsite system is absorbed and properly treated. The LTAR is determined by a number of factors. Certainly, the rate effluent can move through the most hydraulically limited soil horizon and has a great effect on the LTAR. The type of bio mat that forms at the infiltrative surface and the type of system also affect the LTAR. A specific LTAR is based on the total soil and site evaluation. For conventional systems or modified conventional systems, the LTAR is the rate per day that wastewater can be absorbed through the bottom of the infiltration trenches and underlying horizons. For low-pressure pipe (LPP) systems, the LTAR rate is the daily rate wastewater is absorbed through the entire drain field area (trenches and the area between them). For conventional onsite systems the LTAR is based upon the most hydraulically limiting soil horizon within 3 feet of the soil surface or 1 foot below the trench bottom, whichever is deeper. |
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Problems with Overestimation and underestimation of LTAR
Most Of the onsite systems have a range of LTARs, depending on the most limiting soil textural grouping. Estimating the LTAR can be difficult because not only must the texture of the most limiting horizon be classified correctly, but “the right rate” must be estimated from a range of rates. Experience with a number of sites and numerous soils will aid in determining a proper value for LTAR. By misclassifying the limiting soil textural horizon or by estimating the wrong LTAR, the entire calculation for the treatment and disposal field area can be altered.
Soil texture is the major soil characteristic that determines the LTAR for any given soil or saprolite. Estimates of LTAR from the LTAR range for a given soil textural class should then be based on site characteristics such as soil depth, structure, colour, consistence, landscape position, and the type of wastewater effluent.
Most Of the onsite systems have a range of LTARs, depending on the most limiting soil textural grouping. Estimating the LTAR can be difficult because not only must the texture of the most limiting horizon be classified correctly, but “the right rate” must be estimated from a range of rates. Experience with a number of sites and numerous soils will aid in determining a proper value for LTAR. By misclassifying the limiting soil textural horizon or by estimating the wrong LTAR, the entire calculation for the treatment and disposal field area can be altered.
Soil texture is the major soil characteristic that determines the LTAR for any given soil or saprolite. Estimates of LTAR from the LTAR range for a given soil textural class should then be based on site characteristics such as soil depth, structure, colour, consistence, landscape position, and the type of wastewater effluent.