What’s the issue?
Water quality in the lower half of the River Dee catchment is downgraded due to range of nutrient and pathogen source pressures. While these are principally agricultural, it is estimated there are at least 4339 individual dwellings with private septic tank systems (STS) in the catchment (SEPA, unpublished data), representing a density of > 2 km-2 and ca. 7 % of the catchment population. (STS are assumed to contribute to nutrient loads, especially in ‘hotspot’ areas where clusters of STS are located near to tributaries. The significance of nutrient and pathogen discharges from STS is particularly important in the Dee because there a large number of private water supplies in the catchment, the freshwater pearl mussel population is in an unfavourable and sensitive condition, and recent evidence that flow patterns are changing, including lower and more frequent low flow conditions. Consequently, reducing pollution from STS is a priority for the area’s catchment management planning group, the Dee Catchment Partnership.
How are we tackling the contributions from septic tanks?
The Dee Catchment Partnership has taken a three step approach to reducing pollution from STS: 1) identifying the hotspots where environmental and public health impacts are likely to be the greatest; 2) undertaking a two-year catchment-wide campaign to raise awareness of good STS management, targeting the hotspot areas; and 3) establishing mechanisms for long-term provision of information and advice. Potential hotspots were identified by comparing three data sets: locations of STS, water quality data and locations of private water supplies. Properties not served by mains sewerage were assumed to be served by a STS, only half of which were registered. Five of the catchment’s tributaries are failing good ecological status under the Water Treatment Directive because they are impacted by P, and modelling studies have indicated that STS contributes ca. 10-14% of the phosphate load in these sub-catchments. One sub-catchment that was particularly impacted had a high density of STS clusters with many close to watercourses, and a high number of private water supplies. This area has been the subject of a targeted awareness raising campaign.
To support awareness raising, a new leaflet was produced and distributed across the catchment at community information points. Local events such as the Tarland show were also attended by members of the team. The leaflet is now sent out (a) by the Local Authority when building warrants are issued in relation to STS installation, (b) by the water regulators (Scottish Environment Protection Agency, SEPA ) when tanks are registered, and (c) by local STS maintenance companies. The leaflet also forms part of a STS roadshow for use in hotspot areas and designed to be transferable to other catchments. The initiative has proved extremely popular (8000+ leaflets distributed; 100+ roadshow visitors) and has been extended to the wider north-east area of Scotland with the aim of eventual Scotland-wide coverage. The work was presented at the 2011 Catchment Science conference in Dublin.
For more information contact: Susan Cooksley