Baseline Water Quality Assessment for a Proposed Solar Farm in Cornwall


A baseline water quality survey was carried out to inform a planning application for a proposed solar farm site in Cornwall. BSG Ecology was also involved in the production of an ecological impact assessment, landscape and ecology management plan, and site supervision post-consent for this development.

Water quality was assessed by sampling the invertebrate families present in the stream on the site and using the Biological Monitoring Working Party (BMWP) to score the assemblage (an industry-standard technique). The rationale behind conducting this survey was to provide baseline data in a reliable and repeatable way so that, if necessary, water quality could be monitored to assess if any impact (positive or negative) has occurred that could be attributed to the development.


Sample points were selected on site and a control point was selected off site. The sample points comprised of reaches, approximately 10 m in length, centred on shallow, fast-moving sections of the streams that were most likely to yield a diverse invertebrate community sensitive enough that changes in biological water quality could be detected in the future. At each sample point, one minute of hand searching and three minutes of kick sampling was carried out.

All invertebrates were collected for later identification in our laboratory, where sample sorting took place to separate all the different families of invertebrate present within each sample. Sorting was carried out by a suitably experienced entomologist using a stereoscopic microscope with the aid of identification literature as necessary.


The BMWP works on the basic principle that freshwater pollution levels affect invertebrate families differently.  Thus, certain families that are most susceptible to pollution score higher points and those families tolerant of polluted waters score lower points.  Accordingly, cleaner watercourses, which have better water quality score the highest number of points, whilst polluted watercourses score the lowest.

An alternative way of expressing the BMWP score is by measuring the Average Score per Taxon (ASPT) score which is based on the BMWP calculations. As with the BMWP score, the higher the ASPT per sample, the cleaner the watercourse.  The cleanest waters might therefore have an ASPT score close to ‘10’, whilst the most polluted waters lie closer to ‘1’, although in general terms, an ASPT greater than the ‘benchline’ mark of ‘5’ is indicative of a watercourse in reasonable condition. Water quality monitoring can be carried out using the same scoring index each time and comparing the results.

Next Steps

The results from the survey will be used to inform future monitoring of the watercourses. Should the client wish to demonstrate that appropriate methods were put in place to safeguard the watercourse during construction or that conditions have improved post-development, the same points can be resampled and assessed to identify any changes to water quality. Use of the same sample points will provide consistency when comparing results. Monitoring of this nature is often required due to planning conditions recommended by regulatory bodies such as the Environment Agency, who may wish to see evidence that good water quality of our freshwater habitats is being maintained through appropriate mitigation measures associated with development affecting the catchment.

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Energy, South West