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Soil Mineral Precipitate Responsible For Septic System Failure

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Eleventh Individual and Small Community Sewage Systems Conference Proceedings, 20-24 October 2007, Warwick, Rhode Island  701P1107cd.(doi:10.13031/2013.24022)
Authors:   Brad D Lee, Darrell G Schulze
Keywords:   Soil absorption field, septic system failure, iron-oxide, manganese-oxides, mineral precipitate

Properly functioning conventional trench septic systems rely on soil hydraulic conductivity to disperse effluent into the soil absorption field. Typically, septic systems installed in coarse-textured soils function very well if managed correctly, but in the last decade 21% of the septic system failures in Elkhart County, IN, occurred on the Tyner loamy sand (mixed, mesic Typic Udipsamment). Upon excavation of a few of these failed septic systems, it was apparent that a mineral precipitate had formed adjacent to the trenches, apparently causing the absorption field to fail. Reducing conditions adjacent to the soil-trench interface resulted in migration of Fe and Mn away from the trench and precipitation under oxidizing conditions about 15 cm from the soil-trench interface. Iron oxides fill pores between the sand grains forming in a continuous band about 2-5 mm thick. Further from the trench, manganese oxides are concentrated in a discontinuous and diffuse zone about 25 mm thick.

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