Lysimtery versus Deep Water Content Monitoring: Field Performance Evaluation of Alternative Landfill Covers

Two methods were used to compute deep percolation from soil water content data. The pressure gradient between the two deepest water content sensors and the water content recorded at the deepest sensor assuming a unit gradient were considered. Results suggest that assuming a unit gradient grossly overestimates percolation through the soil cover. Estimation by the use of the pressure gradient between the two deepest water content sensors resulted in fairly close percolation as compared to percolation measured using lysimeters. However, reliability of the sensors to estimate percolation through soil covers is still questionable because daily percolation data doesn't compare well with daily percolation measured by lysimeters. Lysimeters are therefore the best method to estimate percolation. Water-content sensors can still be useful as a secondary monitoring tool.