Soil Water Content Monitoring Using Electromagnetic Induction

The use of electromagnetic (EM) induction measurements was evaluated to predict water content in the upper 1.50 m of a prototype engineered barrier soil profile designed for waste containment. Water content was monitored with a neutron probe, and bulk soil electrical conductivity was monitored with a Geonics EM38 ground conductivity meter at ten locations at approximately monthly intervals over a three-year period. A simple linear regression model accurately predicted average volumetric water content of the profile at any location at any time (R2 = 0.80,(sigma)= 0.009) and spatially averaged volumetric water content over the entire area at any time (R2 = 0.99,(sigma)= 0.003). Although some temporal drift was present in the model residual values, the impact on predicted water content was negligible. Therefore, once the model is calibrated with the neutron probe over a sufficient range of water contents, further neutron probe measurements may not be necessary. EM induction has several advantages over traditional water content monitoring techniques, including nonradioactivity, speed and ease of use over larger areas, and noninvasive character.