Influence of well preparation on field-saturated hydraulic conductivity measured with the Guelph Permeameter

An investigation on the influence of the well preparation technique on field-saturated hydraulic conductivity, K-fs measured with the Guelph Permeameter (GP) method was performed in a sandy loam soil. In particular, the influence of adopting the following procedures to prepare the well was investigated: use of a wire screen insert to prevent sinking of the water outlet tip of the GP into the base of the well during a measurement; use of a metallic, sharpened rod to remove the smear layer created during the digging process from the well walls. The influence of the well radius and the antecedent soil water content on the K-fs estimates was also evaluated. Five different types of wells were prepared. Higher and less variable K-fs values were obtained from the wells treated with the wire screen insert and the metallic rod than from the non-treated ones. These results were consistent with the hypothesized occurrence of sinking and smearing phenomena in the non-treated wells and with the effectiveness of the used procedures to prevent or reduce the influence of these phenomena on the K-fs measurement. The estimates of field-saturated hydraulic conductivity increased with the radius of the well. Differences between the sampled soil volumes and a more pronounced influence of sinking phenomena in the small-size wells likely contributed to produce this result. In relatively dry soil conditions, the antecedent soil water content did not affect the K-fs measurements, independently of the well preparation technique. (C) 1997 Elsevier Science B.V.