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Methods for measuring saturated hydraulic conductivity (Ksat) of soils are standardized, but the regulations governing the percolation test vary considerably among states. The objectives of this paper are to present an overview of selected procedures for measuring Ksat, and to compare Ksat obtained by the constant-head well permeameter method with percolation rate values for different conditions. Three different models for calculating Ksat were compared and the Glover solution was selected for comparison with percolation rate. Using various hole diameters (2r) and depths of water in the hole (H), different flow rates were used to calculate a Ksat value and a percolation rate for each r and H combination. In general, the relationship between percolation rate and Ksat obtained from the rate of water flow from a given hole is logarithmic. However, this relationship is not unique and depends on r and H. for any given Ksat value, percolation rate increases linearly with increasing r. As a result, for a given soil, different values of percolation rate can be obtained by changing the radius of the test-hole and the required depth of water in the hole within a given set of regulations. For designing septic systems, the percolation test must be standardized or Ksat measurements be used for determining and/or confirming loading rates.
drainfield sizing, loading rate, percolation test, vadose zone, wastewater disposal
Professor, North Carolina State University, Raleigh, NC