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Appears in Collections:Biological and Environmental Sciences Journal Articles
Peer Review Status: Refereed
Title: Eliciting expert judgements to underpin our understanding of faecal indicator organism loss from septic tank systems
Author(s): Mzyece, Chisha Chongo
Glendell, Miriam
Gagkas, Zisis
Quilliam, Richard S.
Jones, Ian
Pagaling, Eulyn
Akoumianaki, Ioanna
Newman, Claire
Oliver, David M.
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Keywords: Pollution
Waste Management and Disposal
Environmental Chemistry
Environmental Engineering
Issue Date: Apr-2024
Date Deposited: 3-Mar-2024
Citation: Mzyece CC, Glendell M, Gagkas Z, Quilliam RS, Jones I, Pagaling E, Akoumianaki I, Newman C & Oliver DM (2024) Eliciting expert judgements to underpin our understanding of faecal indicator organism loss from septic tank systems. <i>Science of The Total Environment</i>, 921.
Abstract: Septic tank systems (STS) in rural catchments represent a potential source of microbial pollution to watercourses; however, data concerning the risk of faecal indicator organism (FIO) export from STS to surface waters are scarce. In the absence of empirical data, elicitation of expert judgements can provide an alternative approach to aid understanding of FIO pollution risk from STS. Our study employed a structured elicitation process using the Sheffield Elicitation Framework to obtain expert judgements on the proportion of FIOs likely to be delivered from STS to watercourses, based on 36 scenarios combining: (i) septic tank effluent movement risk, driven by soil hydro-morphological characteristics; (ii) distance of septic tank to watercourse; and (iii) degree of slope. Experts used the tertile method to elicit a range of values representing their beliefs of the proportion of FIOs likely to be delivered to a watercourse for each scenario. The experts judged that 93 % of FIOs would likely be delivered from an STS to a watercourse under the highest risk scenario that combined (i) very high STS effluent movement risk, (ii) STS distance to watercourse <10 m, and (iii) a location on a steep slope with gradient >25 %. Under the lowest risk scenario, the proportion of FIOs reaching a watercourse would likely reduce to 5 %. Expert confidence was high for scenarios that represented extremes of risk, while uncertainty increased for scenarios depicting intermediate risk conditions. The behavioural aggregation process employed to obtain a consensus among the experts proved to be useful for highlighting both areas of strong consensus and high uncertainty. The latter therefore represent priorities for future empirical research to further improve our understanding of potential pollution risk from septic tanks and in turn enable better assessments of potential threats to water quality in rural catchments throughout the world where decentralised wastewater systems are common.
DOI Link: 10.1016/j.scitotenv.2024.171074
Rights: © 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (

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