Recent advances in moisture monitoring using tensiometers has allowed long-duration, high quality data sets from within the deep vadose zone. A network of about 30 advanced tensiometers in 18 wells provided field-scale data to monitor moisture conditions and movement in the subsurface in and around a mixed waste disposal site at depths ranging from 6 to over 67 m below land surface (bls). Sensors are located in both sediments and fractured rock within the geologic profile and some have been in operation for over 10 years. The moisture monitoring was able to detect long term declines in moisture content presumably in response to lower than normal precipitation and resultant infiltration over the time period from 2000 to 2004. This trend was reversed in 2005 and 2006 in more than half of the monitoring sites over the 6 to 33 m depth interval and in several monitoring sites from 33 to 67 m, in response to normal to above normal precipitation. This tensiometer data can be used to evaluate the appropriateness of the current conceptual model of flow at this site. It also shows that a moisture monitoring system should be effective to rapidly validate that a proposed remedial action (such as placement of an ET cover) would be effective in reducing the moisture movement to levels similar to those in undisturbed sites outside of the disposal area.
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