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In the absence of data on the source strengths of pollutant loads prioritisation will
undoubtedly be subjective to some degree. However, the methodology of impact
prediction developed for Environmental Impact Assessment (EIA) provides a relatively
objective framework to support the decision-making process. This method aims
to assess the significance of impacts on the environment based on most notably
the sensitivity of the environmental resource, and the perceived magnitude of the
impacts on that resource. The process avoids any sort of numerical scoring, and
still requires a good deal of reasoned professional judgement, but can be used to
determine broad significance ‘thresholds’ which allow prioritisation of mitigation
measures (Table 1).
Table 1:
Significance based on sensitivity of receptor and magnitude of
impact
Magnitude
Sensitivity
Low Medium High
High Moderate Substantial Substantial
Medium Slight Moderate Substantial
Low Slight Slight Moderate
SEPA recently commissioned the preparation of three linked documents in order
to provide a systematic methodology for identifying farm scale diffuse pollution
and for implementing strategies to alleviate problems (SEPA, 2006). The first part,
‘Farm scale diffuse pollution audits’, sets out a methodology for carrying out diffuse
pollution audits on farms and includes standard audit forms to aid this process.
The second part, ‘Siting and suitability of BMPs’ sets out guidance on selection of
suitable mitigation measures for problems identified in the audit. The third part, the
‘BMP Manual’ contains descriptions of a wide range of possible BMPs to address
diffuse pollution issues organised in a way to facilitate selection. The guidance is
meant to help those charged with addressing agricultural diffuse pollution issues
in practice. It will prove useful to catchment management planners in priority or
problem catchments, to regulators, and to advisors and consultants to farmers as
they try to comply with a support regime that will increasingly stress environmental
protection in compliance with government policy. Launching the guidance on the
web will allow field advisers to pilot and amend where necessary, before publishing
the hardcopy and CD.
Sensitivity
For the purposes of assessing diffuse pollution impacts, the sensitivity of the
environmental resource and the likely magnitude of the impact must be considered
for each pollutant in turn. Sensitivity may be determined at a catchment scale or
by some factor specific to the farm (e.g. the presence of a neighbouring designated
site or the soils present on the farm). Before undertaking any work in the field, an
assessment should be made of the catchment containing the farms in question.
Certain catchments will be more sensitive to certain pollutants and it is important
that an appreciation of such sensitivity is built into the subsequent field work. Some
catchments will be more prone to certain types of diffuse pollution and this should
be borne in mind when surveying. A targeted approach that focuses on ‘priority
catchments’ is proposed such that the accumulative benefit of adopting BMPs can
be gained and effectiveness measured. Examples are given below:
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