A review of available technologies for monitoring leaks from underground storage tanks and surface impoundments was performed to identify equipment that was most suited for this purpose. A single probe that combines the functions of a tensiometer and lysimeter was selected for additional research based upon this review. The unit detects changes in matric potential when functioning as a tensiometer and can also collect soil pore-water samples as a lysimeter. The probe developed from this effort was instrumented for both manual or remote monitoring, recording, and sampling. Instrumentation for automated maintenance allowed the unit to operate for extended periods of time without refilling the tensiometer mode of the probe with liquid.
Probe density depends upon soil texture and moisture content, geometry of the containment structure, and depth of installation. Calculations for determining the optimum probe placement based upon the diameter of the porous ceramic portion along with soil dispersion characteristics determine the primary variables for determining the optimum number of probes for a given containment structure. Probe sensitivity is controlled by the porous surface to vessel liquid volume, the radius of the porous section, and type of surface instrumentation.