Consequences of preferential flow in cracking clay soils for contamination-risk of shallow aquifers

A method is presented to asses the contamination risk of aquifers covered with cracking clay soils, with special emphasis on preferential flow through shrinkage cracks. A water extraction area was divided into units with homogeneous soil types and hydrological conditions. For each unit, a one-dimensional computer simulation model was used to compute residence times in the unsaturated zone of the clay soils. Analytical equations were used to estimate residence times in the saturated zone. Finally, a classification system is proposed to visualize the model computations. The method developed is illustrated by a case-study.