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AN INITIAL ASSESSMENT OF THE SUITABILITY OF
TOTAL MAXIMUM DAILY LOADS (TMDLs) AS A MEANS
OF MANAGING DIFFUSE POLLUTION UNDER THE
WATER FRAMEWORK DIRECTIVE
RJ Cooper 1 , RC Ferrier 1 , RD Harmel 2 , SJ Langan 1 , AJA Vinten 1 and MI Stutter 1
1
The Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, UK, E-mail: r.cooper@
macaulay.ac.uk; 2 USDA-ARS, 808 E. Blackland Road, Temple, Texas, 76502, USA
SUMMARY
In the United States, the control of diffuse pollution is addressed by the Total
Maximum Daily Loads programme. In this paper, we assess whether this programme
is suitable for use under the Water Framework Directive, and identify two key issues
concerning the setting of water quality standards and uncertainty.
INTRODUCTION
The Water Framework Directive (WFD) raises a number of challenges for water
quality regulation in the UK, one of which concerns the identification, quantification
and control of diffuse pollution inputs to water bodies. With the initial diffuse
pollution characterisation and impacts analysis now complete, and the monitoring
programmes about to be implemented, attention must now turn to the setting of
environmental objectives and the design and implementation of programmes of
measures (POMs) to control diffuse pollution inputs. While the WFD provides a
basis for the development of legislation in this respect, an appropriate regulatory
framework has yet to be established. In the United States (US), the control of diffuse
pollution is addressed by the Total Maximum Daily Loads (TMDL) programme, which
provides a framework within which linkages between diffuse pollution sources and
impacts are assessed, and permissible loads accordingly defined. The purpose of
this paper is to introduce the TMDL concept, demonstrate its application using the
Tarland Burn in NE Scotland as a case study, and discuss its suitability as a means
of managing water quality under the WFD.
THE TMDL CONCEPT
Over the past 30 years, water quality management in the US has focussed mainly
on the control of point source pollution, via effluent-based water quality standards
established under the Clean Water Act (CWA). Although this has resulted in a general
improvement in water quality, in 2000 over 36 % of water bodies still did not meet
the CWA goal of being ‘fishable, swimmable’, due to inputs of pollutants such as
nutrients and sediment from diffuse sources such as agriculture and urban runoff
(Boyd, 2000). Consequently, there has been a recent shift in the focus of water
quality management from effluent-based to ambient–based water quality standards.
This is the context within which the Environmental Protection Agency (EPA) is
obligated to implement the TMDL programme, the objective of which is attainment
of ambient water quality standards through the control of both point source and
diffuse pollution.
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