Standard Test Method for Determination of Infiltration Rate and Calculating Field Hydraulic Conductivity of Field Soils by Sealed Single-Ring Infiltrometer and Multiple Pressure Head Procedure

Abstract

5.1 This test method shall only be used on soils having infiltration rates ranging from 2.5 mm/h (6.9 × 10–7 m/s) to 1200 mm/h (3.3 × 10–4 m/s). 5.2 This test method provides the means to quantify field hydraulic conductivity (Kf) based on multiple pressure heads, infiltration rate of water, infiltrometer radius, insertion depth, and sorptivity or capillary head. Kf and infiltration rate are similar values that share units, but there is a distinct difference between the two. Infiltration rate does not include corrections for lateral flow, hydrostatic pressure head, and geometric factors of the ring. Kf indicates the maximum hydraulic conductivity possible under natural field conditions. 5.3 This test method is useful for field measurement of the infiltration rate and calculation of field hydraulic conductivity of soils. It is intended for use in applications such as stormwater management design, preliminary and post construction soil evaluation, and annual testing on surface drainage systems like rain gardens and other bioretention basins. Other suitable applications include evaluation of potential septic-tank disposal fields (ASTM D5879 and D5921), leaching and drainage efficiencies, irrigation requirements, erosion potential, forestry, agriculture, and water spreading and recharge, among others. This test is not intended for use in hydraulic barriers/seals such as landfill liners, nuclear waste repositories, or the core of a dam. This test is also not intended for use in soils that experience changes in volume during infiltration, such as collapsible or expansive soils. 5.4 Field hydraulic conductivity can only be calculated when the hydraulic boundary conditions are known, such as hydraulic gradient and the extent of lateral flow of water, or these can be reliably estimated. Note 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors. 5.5 The multiple head analysis analyses approach allows for the determination of the field hydraulic conductivity and matric flux potential when measuring infiltration using two consecutively ponded heads in a single-ring infiltrometer, based on the equations developed by Reynolds and Elrick, 1990 (1). Consequently, this analysis also enables the estimation of the Green- Ampt wetting front pressure head. 5.6 Many factors affect the infiltration rate, including soil structure, soil layering, condition of the soil surface, degree of saturation of the soil, chemical and physical nature of the soil and of the applied liquid, head of the applied liquid, temperature of the liquid, and diameter and depth of embedment of rings. Therefore, tests conducted at the same site are unlikely to yield identical results. The rate measured by the test method is primarily for comparative use.