Electrical conductivity helps locate septic-system failure.

An instrument that can measure how well soil conducts electricity also can spot the source of septic-system failures without the need to destroy a whole yard with a backhoe.

The instrument, called a non-invasive electromagnetic induction (EMI) sensor, measures electrical conductivity on the basis of soluble salts, water, temperature, and percentage of clay in the soil. Purdue University researchers and colleagues tested the tool on a failed septic system in northeastern Indiana and found that soil conductivity changes can signal septic failure.

They found that the sensor was capable of collecting soil data that identified problems in the septic tank and septic-field trenches, said Brad Lee, an assistant professor of agronomy at Purdue. The findings have been published in the online journal Vadose Zone, a publication of the Soil Science Society of America.

"One of the big problems in looking for septic-system contamination is that homeowners don't want their lawns dug up," Lee said. "The sensor can help investigators locate problems without digging. This is possible because soil contaminated with household waste has a higher electrical conductivity than the readings from the rest of the lawn."

The electromagnetic sensor is portable, collects data quickly, and can measure down to many soil depths, he said. In addition, maps prepared from sensor data can be used to assess building sites, plan future testing, and locate the best sites for sampling and monitoring of soil.

The tool previously had been used to test for animal waste, to determine salinity in agricultural areas, and to locate storm sewers and buried landfills.

In December 2001, Lee and his team used the sensor at a home in Allen County, Indiana, at which a failed septic system was believed to be leaking contaminants into the ground adjacent to the septic system trenches. They confirmed the hypothesis when readings of electrical conductivity were higher in the septic field than in the adjacent property. The researchers retested the area in July 2002 after the owners had moved and the system had not been used for six months. At that time, the readings around the septic field were comparable to those in the surrounding land.

The scientists now know that the sensor works in the fine-textured, glacial soils of northeastern Indiana, Lee said.

Further studies are planned to confirm that the sensor also will be effective in other soil types and environmental conditions.

The other researchers involved in the study were Byron Jenkinson, a consulting soil scientist; James Doolittle and J. Wes Tuttle, of the USDA Natural Resource Conservation Agency; and Richard Taylor of Dualem, Inc., in Milton, Ontario, Canada.

The Indiana Water Resources Research Center and the Fort Wayne/Allen County Health Department provided the funding for the project.