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ORIGINAL RESEARCH

Electrical Conductivity of a Failed Septic System Soil Absorption Field

^a Agronomy Dep., Purdue Univ., West Lafayette, IN 47907
^b USDA-NRCS-NSSC, 11 Campus Blvd., Suite 200, Newton Square, PA, 19073
^c Dualem Inc., 540 Churchill Ave., Milton, ON, Canada L9T 3A2
^d USDA-NRCS-NSSC, P.O. Box 60, Wilkesboro, NC 28697
^* Corresponding author (bdlee{at}purdue.edu)

Received 23 September 2005.

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 noninvasive 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-2) 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 (EC_a) was significantly correlated to unweighted average electrical conductivity from soil saturated paste extracts (EC_sat; r = 0.79). The EC_a below the soil absorption field was higher than the surrounding native soil under both dry and wet soil moisture conditions. Individual soil absorption trenches had a higher EC_a than background EC_a under both soil moisture conditions. A higher EC_a 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 6 mo. 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.

Abbreviations: EC_a, apparent conductivity • EC_sat, saturated paste extract electrical conductivity • EMI, electromagnetic induction • HCP, horizontal coplanar • PRP, perpendicular