A preliminary investigation regarding the removal of selected Contaminants of Emerging Concern (CEC) by shallow soils-based onsite septic system technologies was conducted at the Massachusetts Alternative Septic System Test Center in 2010 – 2012. Untreated septic tank effluent was applied to a shallow (less than 9 inches) soil horizon in lined test cells. We report that removal efficiencies of selected pharmaceuticals, hormones and personal care products in drip dispersal systems are generally higher than those levels reported for non-soils-based treatment technologies. The removal efficiencies of the selected compounds using drip dispersal reported approach 100%. The data suggest that septic systems employing shallow soils-based means for ultimate disposal may offer comparable to better treatment for certain micro-constituents of wastewater compared to some municipal wastewater treatment facilities. The fire retardant TCEP (Tris (2-chloroethyl) phosphate) was not attenuated during treatment and, similar to the conclusion reached in other studies, may prove to be a particular challenge for wastewater treatment removal strategies.
One additional objective of the present study was to evaluate the effect of supplementing the drip dispersal system with air. Additional air (3 – 5 psi @ 3 – 5 cfm) was provided through the drip dispersal network at times when effluent was not being applied. Soil-gas measurements revealed no significant and consistent differences in the achievement of atmospheric levels of oxygen between the treatments. Accordingly, the absence of significant differences between CEC removal efficiencies may not be representative of the impacts of supplemental-air. It is posited that the small orifices of the drip system may not allow enough air into the immediate soil profile in significant amounts higher than that of the natural air movement in the non-treated test cells