Summary: PROOF COPY [HE/2006/023075] 002808QHE
Effects of Sand Depth on Domestic Wastewater Renovation
in Intermittently Aerated Leachfield Mesocosms
José A. Amador1
; David A. Potts2
; Erika L. Patenaude3
; and Josef H. Görres4
Abstract: The depth of soil below the absorption trench of a septic system is considered an important factor in protection of groundwater.
We examined the effects of depth on the ability of intermittently aerated sand-filled leachfield mesocosms to renovate domestic waste-
water. Mesocosms n=3 consisted of lysimeters with a headspace O2 concentration maintained at 0.21 mol/mol and containing 7.5, 15,
or 30 cm of sand that were dosed with septic tank effluent every 6 h for 328 days 12 cm/d . Sand depth had no effect on pH, dissolved
O2, PO4, NH4, or BOD5 levels in percolate water. Nitrate levels in percolate water were higher for 30 cm than for 7.5 and 15 cm during
the first 70 d of the experiment, after which no differences were observed. Time-averaged removal rates of N, P, fecal coliform bacteria,
and BOD5 were 2228, 1318, 8192, and 8199%, respectively, and were unaffected by depth. Wastewater renovation in intermittently
aerated leachfield mesocosms appears to take place in a narrow zone 7.5 cm below the infiltrative surface, with the medium below
contributing little to renovation.