Case study:Septic Tank Survey in the Clun Forest

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Location: 52° 26' 28.21" N, 3° 9' 36.78" W

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Project overview

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Status	Complete
Project web site
Themes	Social benefits, Water quality
Country	England
Main contact forename	Bob
Main contact surname	Harris
Main contact user ID	User:Dolcoath
Contact organisation	Land Life and Livelihoods
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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The catchment of the Upper Clun and its tributaries is largely unsewered and, although the population density is low, the contribution of septic tanks adding nutrients to the river needs to be better understood. The river is classified to be of high quality but a Special Area of Conservation (SAC) at the lower end is being degraded and there are other signs of freshwater related biodiversity decline. Nutrients play their part, but some of this decline is believed to be due to the deposition of sediment in the riverbed. The river is heavily silt-laden when in spate and this is particularly noticeable in the upper reaches. The steep slopes and high rainfall in the Upper Clun are likely to lead to proportionately high soil erosion and rapid transport with roads acting as conduits and drains as pathways for more rapid transport to the river. This is a community-led and Environment Agency financed review of the state of septic tanks and road drains in the Upper Clun catchment.

Monitoring surveys and results

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A small group of people organised by Land Life and Livelihoods were able to obtain information through questionnaire and interview from 66% of the households with septic tank sewerage systems in the area. In general there was a low degree of awareness of how tanks worked, but people in the locality seem to have readily addressed problems when they have arisen. 52% of tanks are over 30 years old and 37% of soakaway systems being within 25m of a watercourse. The majority of householders (54%) have their tanks desludged frequently (<3 yrs) but a significant proportion (16%) wait 10 yrs or longer. A risk assessment was carried out using the information collected and a ranking list drawn up. Only 3 (2%) systems showed obvious signs of failure and need attention, although the condition of tanks was not physically inspected. Some systems are in high-risk locations but without obvious signs of malfunction and in the absence of supporting water quality data it is difficult to determine whether they are working effectively. Recommendations are made for improvements to the 3 sites and further investigation of the remaining higher-risk sites.

The investigation of the flux of silt and sediment from hillsides and road verges via the road system suggested that roads were major carriers of sediment and that as well as some road drains, overflows from accumulated water and ditches alongside roads also needed to be considered. However, road drains are mostly located in the valley bottoms and so dealing with them is akin to treating the symptom rather than the root causes. The report suggests that a whole catchment analysis of the erosion and sediment transport issues is needed of which managing road drains should play a part.

Lessons learnt

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The overall conclusions are that without water quality data, it is not certain how big an impact on water quality unsewered properties are having. On the face of it, septic tanks do not present as big an issue for river ecology as soil erosion and sediment transport and that a whole catchment approach to understanding the pressures is needed.

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Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body National/international site designation Local/regional site designations Protected species present Invasive species present Species of interest Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information