Impact of density on the hydraulics of peat filters

• Published in: Canadian geotechnical journal Vol. 38; no. 6; pp. 1213 - 1219
• Main Authors: Kennedy, Paula L, Van Geel, Paul J
• Format: Journal Article
• Language: English
• Published: Ottawa, Canada NRC Research Press 01-12-2001; National Research Council of Canada; Canadian Science Publishing NRC Research Press
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Engineering geology; Environmental aspects; Exact sciences and technology; Hydraulics; Mosses; Peat; Septic tanks; Sewage disposal; Canada; Canada, Ontario; Canada, Ontario, Ottawa; experimental studies; models; density; porosity; simulation; effluents; flow mechanism; pressure; North America; water; unsaturated zone; hydraulic conductivity; hydraulics; depth; burial; drainage; soils; tensiometers; peat; filtering; retention
• ISSN: 0008-3674; 1208-6010
• DOI: 10.1139/t01-047

Peat filters have been used to treat septic tank effluents from domestic and commercial sources, landfill leachate, and acid mine drainage. A better understanding of the hydraulics and impact of the organic loading on these types of systems will enhance the application of peat filter systems. This paper presents the results of a field study to evaluate the hydraulics of a peat filter used to treat the septic tank effluent from a public school west of Ottawa, Ontario, Canada. The filter was instrumented with tensiometers and transducers to monitor the pore-water pressures in response to a pulse of septic tank effluent. Samples of peat were collected to determine the dry density profile with depth. The soil moisture retention curve, effective porosity, and hydraulic conductivity as a function of dry density were determined in laboratory experiments. A one-dimensional unsaturated flow model was used to predict the pressure response due to a pulse. Two model scenarios were evaluated to demonstrate the impact of density variations on model simulations. Model simulations that accounted for dry density variations with depth measured in the field more accurately simulated the pressure responses measured in the field.Key words: unsaturated flow, peat, filters, septic, modelling, density.