Significance and Use
5.1 This practice shall only be used on soils having infiltration rates ranging from 2.5 mm/h (field hydraulic conductivity of 6.9 × 10-7 m/s) to 15000 mm/h (field hydraulic conductivity of 4.0 × 10-3 m/s).
5.2 This practice is useful for field measurement of the infiltration rate and calculation of field hydraulic conductivity of soils. It was initially developed for stormwater treatment applications, and has been used to design, verify the construction of, and perform annual testing on surface drainage applications such as rain gardens or storm water collection systems (1). 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 other applications. 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.
5.3 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 facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
5.4 A mathematical analysis has been developed for this test that follows the Green-Ampt analysis that assumes a relationship between the volumetric water content and the depth of the wetting front, in that volumetric water content profile at the wetting front is represented by a sharp transition between the initial value in the ground and that of saturated soil, that is, the porosity (1), (2).
5.5 Many factors affect the infiltration rate, for example the 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. Thus, tests made at the same site are not likely to give identical results and the rate measured by the practice described in this standard is primarily for comparative use.
Scope
1.1 This practice describes a procedure for field measurement of the infiltration rate of liquid (typically water) into soils using the modified Philip Dunne (MPD) infiltrometer. The data from the field measurement is then used to calculate the field hydraulic conductivity. Soils should be regarded as natural occurring fine or coarse-grained soils or processed materials or mixtures of natural soils and processed materials, or other porous materials, and which are basically insoluble and are in accordance with requirements of 5.1.
1.2 This practice may be conducted at the ground surface or at given depths in pits, on bare soil or with vegetation in place, depending on the conditions for which infiltration rates are desired. However, this practice cannot be conducted where the test surface is at or below the groundwater table, a perched water table, or the capillary fringe.
1.3 This practice is for soils within a range of infiltration rate range defined in 5.1, as long as an adequate seal can be made between the MPD Infiltrometer base and the soil being tested. In highly permeable soils, readings can be taken at shorter intervals, to ensure that enough data are collected to determine the infiltration rate.
1.4 The field measurement is a falling head test that can be performed relatively quickly (30 to 60 minutes) in silty sand or clayey sand soils suitable for stormwater infiltration practices. It is suitable for testing several locations across a site, to characterize the spatial variability of the infiltration rate throughout the site.
1.5 The field measurement can be used to measure the infiltration rate, which can be used to calculate the field hydraulic conductivity. The field hydraulic conductivity can be used as an index to compare the suitability of soils for use in the development of surface drainage applications (for example, rain gardens or stormwater fills).
1.6 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are to be included in this standard.
1.7 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.8 The procedures used to specify how data are collected/recorded or calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analytical methods for engineering design.
1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
