The increased awareness for the need of properly treated wastewater has driven authorities in recent years to conservatively only consider optimum soil types and condition for septic system absorption field construction. The use of reworked or disturbed soil has been avoided regardless of soil type, which has significantly limited the ability for landowners and contractors to utilize less than optimum construction sites at reasonable costs.
The performance of disturbed soil to treat basic wastewater indicator parameters of septic tank effluent was evaluated over 115 days using laboratory soil columns. The wastewater was obtained from a septic tank serving an occupied single family home. Five inch diameter test columns were prepared in triplicate with soil thicknesses of zero (control), 9 and 18 inches. A silt loam Darien series soil was utilized following grain size analyses and basic soil chemistry determination.
The wastewater treated by the soil columns was analyzed for fecal coliform, total suspended solids and biochemical oxygen demand (5-day). These results were compared against the wastewater from the septic tank to establish percent removal.
Results from the soil columns showed significant removal rates of fecal coliform, total suspended solids, and biochemical oxygen demand (5-day) that were as high as 90%. The results demonstrated that treatment of residential wastewater can be achieved using 9 or 18 inches of a disturbed Darien soil.