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

The instrument, called a non-invasive electromagnetic induction (EMI) sensor, measures electrical conductivity based on the 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, a Purdue assistant professor of agronomy. The findings are reported in the online journal Vadose Zone, a publication of the Soil Science Society of America.

"One of the big problems of looking for septic system contamination is that homeowners don't want their lawns dug up," Lee said. "The sensor can help scientists 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 instrument identifies these changes in soil electrical conductivity".

Using the electromagnetic sensor is advantageous because it's portable, it collects data quickly and it 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 for possible septic contamination.

The tool previously had been used to test for animal waste, salinity in agricultural areas, and to locate storm sewers and buried landfills, however, it had never been used before to find problems in septic systems.

In December 2001, Lee and his team used the sensor at a home in Allen County, Ind., that was believed to have a failed septic system leaking contaminants into the ground adjacent to the septic system trenches. They confirmed this 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 system had not been used for six months after the owners moved. At that time, the readings around the septic field were comparable with the surrounding land.

Based on their study, the scientists know that the sensor works in the fine-textured, glacial soils of northeastern Indiana, Lee said. Further studies are planned to confirm that it also will be effective in additional 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 U.S. Department Agriculture-Natural Resource Conservation Agency; and Richard Taylor of Dualem Inc., Milton, Ontario, Canada.



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