Natural Resources Conservation Service NRCS Permeability Classes for Saturated Soil

Permeability Class

Very slow Slow

Moderately slow Moderate Moderately rapid Rapid Very rapid

Permeability (cm/hr)

<0.15 0.15-0.5 0.5-1.5 1.5-5.1 5.1-15.2 15.2-50 >50

Permeability (in./hr)

<0.06 0.06-0.2 0.2-0.6 0.6-2.0 2.0-6.0 6.0-20 >20

Source: Adapted from USEPA, Process Design Manual: Land Treatment of Municipal Wastewater, EPA 6125/1-81-018, CERI, Cincinnati, OH, 1981.

2.3.2 Infiltration and Permeability

The ability of water to infiltrate the soil surface and then percolate vertically or laterally is a critical factor for most of the treatment concepts discussed in this book. On the one hand, excessive permeability can negate the design intentions for most ponds, wetlands, and OF systems. Insufficient permeability will limit the usefulness of SR and SAT systems and result in undesirable waterlogged conditions for land application of biosolids. The hydraulic properties of major concern are the ability of the soil surface to infiltrate water and the flow or retention of water within the soil profile. These factors are defined by the saturated permeability or hydraulic conductivity, the infiltration capacity, and the porosity, specific retention, and specific yield of the soil matrix.

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