An Improved Zero‐Tension Lysimeter to Monitor Colloid Transport in Soils

Abstract

AbstractMobile colloids may facilitate the long‐distance transport of actinides, organic contaminants, and heavy metals in soil, surface water, and groundwater. Detection of colloid‐facilitated contaminant transport in soils requires adequate monitoring before, during, and after in‐situ remediation treatments. Zero‐tension lysimeters (ZTLs) are devices designed to collect water that moves through the soil under the influence of gravity; they can also be used to collect mobile colloids. A ZTL that is suitable for monitoring colloid‐facilitated contaminant migration consists of a specially designed collection cup placed below an undisturbed core of soil that has been initially withdrawn with a hydraulically powered tube. Field tests of the lysimeter were conducted at a site near Ames, IA, where three levels of municipal sewage sludge were applied to the soil in 1992. Each ZTL required about 45 min for a two‐person crew to install at 50‐cm depth. Turbidity measurements of leachate following summer storms revealed considerable spatial variability in colloid migration, supporting the use of ZTLs that can be installed quickly and cheaply in large numbers at a study site. The ZTL described has significant advantages over conventional designs with respect to simplicity and speed of installation. Therefore, it allows colloid transport to be monitored at more locations at a given site. In addition, because of the improved spatial resolution in sampling and monitoring, if contaminants are mobilized, their source can be more easily identified than with piezometer‐based monitoring methods.