Long-term in-situ monitoring and modelling of water quality

Final effluent from Sewage Treatment Works (STW) has good connectivity to watercourses, continuous flow during ecologically-sensitive periods and emergent pollutants. These characteristics make their permitted management an environmental policy issue at national scale. Reliable quantification of STW loadings is essential for the development of targeted, cost-effective and equitable catchment management strategies for the improvement of water quality and ecological status. In this context, our recent work has integrated up-to-date information on consented discharge permits, data from the associated monitoring certification scheme (MCERTS) and archived water quality data in the Water Information Management System (WIMS) to estimate updated annual loadings of total phosphorus and suspended solids for STWs across England. While STWs managed by both water companies and non-water companies were considered, the current work has focused on those which record freshwater as their principal receiving environment. Statistical relationships between 1) permitted flow and actual daily flow, and 2) prescribed pollutant concentration limits and monitored data from regulatory sampling were explored. Annual loadings for individual STWs were calculated, and these exhibit a significant reduction (>80%) in the national scale total loads emitted to freshwater in comparison with our previous estimates for the period 2010-2012. Monte Carlo simulations have also been undertaken to quantify potential ranges for the load estimates. These estimates should, however, still be treated with some caution considering the issues of permit registration for those STWs with multiple outlets, the limited number of monitoring sites with good quality data (especially for total phosphorus) and the high variability of monitored concentrations recorded for any individual specified consented discharge. The updated STW loadings will contribute to ongoing cross-sector water pollutant source apportionment work as part of a strategic research programme exploring the cost-effectiveness of targeted on-farm intervention strategies for sustainable intensification.