Practical Experience with the Modified Philip–Dunne Infiltrometer Test

Design, construction, and maintenance of stormwater facilities often require field measurements of hydraulic conductivity. In recent years, the modified Philip–Dunne (MPD) infiltrometer test has been promoted as an efficient option, particularly in rain gardens and other green stormwater infrastructure. However, the literature misses some details on its performance in practice. Based on our experiences building our own equipment, executing the test in various field conditions, and determining hydraulic conductivity for the purposes of engineering design, we describe some limitations for other users to consider and improve upon. The equipment, though simple in concept, required custom metalwork, was vulnerable to damage during soil insertion, and was not always watertight. The infiltrometer was difficult to insert into hard soils, and soil piping, scour, and other complications arose during field tests. The iterative solution for hydraulic conductivity was not always straightforward; some solutions failed to converge or were unreasonable, especially in less permeable soils. Even with successful tests, values varied and necessitated careful interpretation, spatial averaging, and application of appropriate safety factors for design. Despite its limitations, the test remains useful as a minimally invasive, repeatable, and, in permeable soils, rapid method for testing infiltration rates in the field. We recommend that the ASTM standard be updated, that safety factors be developed further, and that MPD users share their data to help advance the practice.