ABSTRACT
Electrical resistance blocks, made of gypsum or other porous materials, have been used to measure soil moisture in agricultural applications for decades. These blocks may be a useful and often overlooked tool for unsaturated zone monitoring applications at landfills or hazardous waste sites. The blocks are most accurate at soil-water tensions between 0.5 to 15 bars. Other common unsaturated zone monitoring devices, such as tensiometers, lysimeters, and manometers, will only operate in the wetter ranges of soil-water tension, below about 0.7 bar. Because they require damp soils, these other instruments are impractical in dry areas, such as the southwestern United States. Electric resistance blocks, however, will operate at conditions ranging from saturation to extreme aridity and, therefore, are well suited for unsaturated zone monitoring applications in the southwest.
