Purdue News

June 16, 2006

Electrical conductivity helps locate septic system failure

WEST LAFAYETTE, Ind.— 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.

Brad Lee with EMI sensor
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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 published 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 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 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.

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


Writer: Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu


Source: Brad Lee, (765) 496-6884, bdlee@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, forbes@purdue.edu

Agriculture News Page


Related Web sites:

Purdue Department of Agronomy

USDA-Natural Resource Conservation Agency

 

PHOTO CAPTION:

Homeowners may no longer be forced to rip up their yards to find the source of septic tank system failures thanks to Brad Lee, an assistant professor of agronomy at Purdue. Lee has adapted a device that can non-invasively finds the source of such failures. (Purdue Agricultural Communications photo/Tom Campbell)

A publication-quality photo is available at http://news.uns.purdue.edu/images/+2006/lee-electricseptic.jpg

 


ABSTRACT

Electrical Conductivity of a Failed Septic System Soil Absorption Field

Brad D. Lee,* Byron J. Jenkinson, James A. Doolittle, Richard S. Taylor and J.Wes Tuttle

B.D. Lee and B.J. Jenkinson1, Agron. Dep., Purdue Univ., West Lafayette, IN 47907-1150; J.A. Doolittle2, USDA-NRCS-NSSC, 11 Campus Blvd., Suite 200, Newton Square, PA, 19073; R.S. Taylor3, Dualem Inc., 540 Churchill Ave., Milton, ON Canada L9T, 3A2; J.W. Tuttle4, USDA11 NRCS-NSSC, P.O. Box 60, Wilkesboro, NC 28697. (*Corresponding author. bdlee@purdue.edu)

Locating existing septic systems and determining the extent of soil contamination after septic system failure can be destructive, time consuming, and a nuisance to homeowners. The objective of this study was to determine the effectiveness of non-invasive electromagnetic induction (EMI) for locating a failed septic system in fine-textured glacial-till derived soils. Components of a failed septic system were located with a push probe, georeferenced with a theodolite, and surveyed with a dual receiver EMI sensor (DUALEM-21) in December 2001 (wet soil moisture condition) and July 2002 (dry soil moisture condition). Three transects located perpendicular to the soil absorption field trenches were sampled to a depth of 1.2 m and used to ground reference the EMI survey. Near surface (1 m depth) apparent conductivity (ECa) was significantly correlated to unweighted average electrical conductivity from soil saturated paste extracts (ECsat) (r = 0.79). The ECa below the soil absorption field was higher than surrounding native soil under both dry and wet soil moisture conditions. Individual soil absorption trenches had a higher ECa than background ECa under both soil moisture conditions. A higher ECa pattern that was apparent in December 2001 associated with discharge of wastewater at shallow depths was not evident in July 2002 after the system had been abandoned for six months. While more research is warranted, results from this study suggest that electromagnetic induction is a promising technique to identify the location of septic system components, failed septic systems and their associated effluent plumes.

1Mention of trade names is for informational purposes only and does not represent author endorsement.


 

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