24 Jan 2012
“Of course the concentrations are high – you sampled during a period of heavy rain” …
Although a commonplace observation in the old river boards and water authorities of the 1970s, no-one at that time talked about diffuse pollution (contamination associated with wet weather mobilisation of contaminants from land and drainage networks).
In the course of sampling and inspecting many watercourses during a career in NW England and then Scotland, high flows that were characterised by high turbidity were commonplace, and for urban watercourses low flows often showed excellent water quality (chemical parameters), with low measured values for suspended solids, nutrients and BOD (unless adversely impacted by foul into surface water wrong connections). The sediments of those urban streams however, were usually grey and silty, releasing oil when disturbed. Little invertebrate life was to be found. Only at high flows was that true quality revealed, when turbid flows fed by runoff from roads, business parks and other impervious surfaces exerted their influence. In anticipation of the needs of the Water Framework Directive, SEPA investigated sediment quality of nine urban watercourses from Aberdeen to East Kilbride providing a solid evidential basis for characterising urban water quality. As well as recording significant sediment contamination by oil, PAHs and toxic metals, the assessment also reported typically low (poor quality) values for biological indices (Wilson et al 2005).
The need to remove contaminants from contaminated surface water was recognised in the provisions of the Control of Pollution Act, 1974, but not subsequently fully implemented across the UK. That recognition of for example road runoff and persistent pollutants, was perhaps limited, but the impact of surface water from industrial areas was more widely recognised by regulators. Thus for the worst case impacts – typically industrial estates and commercial areas where the quantities and variety of potential pollutants handled and utilised is greater than on other urban surfaces – it was quite usual to licence the discharges of surface water that had been shown to have direct adverse impacts on receiving water quality. The Environment Agency has 655 Industrial Estates with Discharge Consents in England and Wales, 617 in England and 38 in Wales. In Scotland a similar situation was inherited by SEPA on its formation in 1996. Subsequently, under the provisions of The Water Environment (Controlled Activities) (Scotland)Regulations 2005, (the CAR regulations), established under the Water Environment and Water Services Act 2003, the WEWS Act, SEPA as a matter of policy licences industrial estate surface water discharges, and requires provision of treatment by a treatment train of SUDS features. Those discharges were identified by local pollution control staff in the agencies, including environmental impact data obtained by agency ecologists. More recently a broader assessment of likely impacts of a range of urban source diffuse pollutants has been attempted by the development of pollution models to predict pollutant loads and risks of EQS exceedence (Mitchell 2005, Ellis JB and Mitchell G (2006).
Practical pollution control options: BMPs
In the 1980s and subsequent decades, the development of a new approach to address diffuse (or non-point source, NPS, as it was termed in USA) pollution established the BMPs concept: best management practices, measures that an environment agency can promote to address diffuse sources (see Novotny 2003, Campbell et al 2004). These opportunities and their implementation will be explored in the next blog feature. More background to these issues is given in the associated feature article.
Read Brian D’Arcy’s full ‘Water Reflections’ article on this topic in the Resources Section of Engineering Nature’s Way [link]
Read Brian D’Arcy’s first ‘Water Reflections’ Blog. “In the beginning… There was filth”