Variation in septic system effluent inputs to tributaries in multiple subwatersheds and approaches to distinguish contributing pathways and areas

Eliciting Expert Judgements to Underpin Our Understanding of Faecal Indicator Organism Loss from Septic Tank Systems

“…The degree of slope on which STS are situated and their proximity to a watercourse are highly transferable environmental variables and well recognised risk factors (Tyre et al, 2023;Wiesner-Friedman et al, 2022). Although the notion of effluent movement risk, represented by HOST in our study, makes the elicited proportions more representative of the UK, these can be modified to fit classifications of soils and associated hydrological pathways outside of the UK as a generalised concept (Baykus et al, 2022;Tamang et al, 2022). While the three risk factors integrated into our combined scenarios are recognised as key drivers of FIO risk (Glendell et al, 2018), the expert judgements provide only a first approximation of the likelihood of annual FIO delivery from STS to watercourses.…”

“…Eliciting the QoI based on a single factor, for example just slope, rather than integrating all three factors would have been conceptually easier but would not represent how these factors interact in reality. Furthermore, evidence is available for how these factors in isolation influence FIO STS effluent movement risk based on factors such as distance (Tamang et al, 2022), soil properties (Gagkas and Lilly, 2019) and slope (Glendell et al, 2022). Thus the 36 scenarios devised in our study intended to bring this evidence together to explore expert opinion of how these conditions interact to influence FIO delivery.…”

“…This is likely due to several factors, including: a lack of data on septic tank locations in catchments (Withers et al, 2012); poor records of tank maintenance (Akoumianaki and Ibiyemi, 2022), uncertainties regarding tank condition, age, and treatment levels (Richards et al, 2016). Additionally, sampling from intricate diffuse septic tank effluent pathways is complex (Tamang et al, 2022) and generally, there is uncertainty associated with FIO fate and transfer dynamics in response to a suite of varying and interacting environmental variables (Afolabi et al, 2020;Buckerfield et al, 2019b). The lack of quantitative evidence on the contribution of STS to FIO pollution in receiving waters under a range of hydrological and environmental scenarios, especially in rural areas, presents a challenge for regulators and environmental decisionmakers who have a responsibility for managing catchment water quality (Beal et al, 2005;Schwetschenau et al, 2022).…”

Microplastics and nanoplastics in agriculture—A potential source of soil and groundwater contamination?

“…The latter can be especially important in more sparsely populated areas without centralised wastewater treatment and with shallow water tables. While recent studies have demonstrated the potential of soil and groundwater to receive dissolved pollutants such as nutrients or artificial sweeteners from septic tank-based effluent (Tamang et al 2022;Oldfield et al 2020), studies focused on MnPs have yet to be conducted. The aforementioned input and vectors of MnPs into aquifers are important because the presence of plastic particles has been confirmed in source waters of several drinking water treatment plants, raising concern whether current conventional treatment technologies can satisfactorily remove plastic particles (Pulido-Reyes et al 2019).…”