Effluent flux prediction in variably saturated soil zones within a septic tank-soil absorption trench

C D Beal; Ted Gardner; D W Rassam; A M Vieritz; N W Menzies

doi:10.1071/SR06007

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Effluent flux prediction in variably saturated soil zones within a septic tank-soil absorption trench

Journal article

Open access

Peer reviewed

Effluent flux prediction in variably saturated soil zones within a septic tank-soil absorption trench

C D Beal, Ted Gardner, D W Rassam, A M Vieritz and N W Menzies

Australian Journal of Soil Research, Vol.44(7), pp.677-686

2006

DOI: https://doi.org/10.1071/SR06007

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Abstract

biomat zone

septic system

unsaturated flow

HYDRUS-2D

modelling

on-site wastewater

The treatment and hydraulic mechanisms in a septic tank-soil absorption system (SAS) are highly influenced by the clogging layer or biomat zone which develops on bottom and lower sidewall surfaces within the trench. Flow rates through the biomat and sub-biomat zones are governed largely by the biomat hydraulic properties (resistance and hydraulic conductivity) and the unsaturated hydraulic conductivity of the underlying soil. One- and 2-dimensional models were used to investigate the relative importance of sidewall and vertical flow rates and pathways in SAS. Results of 1-dimensional modelling show that several orders of magnitude variation in saturated hydraulic conductivity (Ks) reduce to a 1 order of magnitude variation in long-term flow rates. To increase the reliability of prediction of septic trench hydrology, HYDRUS-2D was used to model 2-dimensional flow. In the permeable soils, under high trench loading, effluent preferentially flowed in the upper region of the trench where no resistant biomat was present (the exfiltration zone). By comparison, flow was more evenly partitioned between the biomat zones and the exfiltration zones of the low permeability soil. An increase in effluent infiltration corresponded with a greater availability of exfiltration zone, rather than a lower resistance of biomat. Results of modelling simulations demonstrated the important role that a permeable A horizon may play in limiting surface surcharge of effluent under high trench hydraulic loading. © CSIRO 2006.

Details

Title: Effluent flux prediction in variably saturated soil zones within a septic tank-soil absorption trench
Authors: C D Beal (Author) - University of Queensland
Ted Gardner (Author) - University of Queensland
D W Rassam (Author) - Queensland Department of Natural Resources, Mines & Water
A M Vieritz (Author) - CSIRO Land and Water
N W Menzies (Author) - University of Queensland
Publication details: Australian Journal of Soil Research, Vol.44(7), pp.677-686
Publisher: C S I R O Publishing
Date published: 2006
DOI: 10.1071/SR06007
ISSN: 0004-9573
Organisation Unit: University of the Sunshine Coast, Queensland
Language: English
Record Identifier: 99450525102621
Output Type: Journal article

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Collaboration types: Domestic collaboration
Web Of Science research areas: Soil Science

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