The Shetland Gas Plant (SGP) is a large gas processing site built in a very fragile ecosystem (blanket bog) at Sullom Voe on the Shetland Islands.

There are multiple environmental designations in the surrounding environment (RAMSAR, SSSI - Site of Special Scientific Interest, MPA, …). The site processes gas and liquid, the produced water effluent from these operations are then fed to the Effluent Water Treatment Plant (EWTP) for processing prior to being discharged to Yell Sound via a 3.75 km pipeline.

There are numerous defined pathways and very sensitive receptors in the area which both the produced water and drainage water could directly impact in a short period of time.

The regulatory regime is very intensive & wide ranging, this allied to the high societal expectations, especially socio-economic, meant that careful design and construction criteria, along with very reactive operational control methodologies, were required to manage the need for continuous monitoring and modifications.

Best Available Technique (BAT) assessments were carried out to determine a predicted contaminant level; actual recorded levels were then compared to the predicted level. Over the course of a lengthy construction and commissioning period, it was found that the output contaminant balance was very complex and susceptible to large movements with small input changes; these were recognised as associated issues (multiple determinands and management of trigger levels).

This required prolonged and intensive adjustment to the process to ensure that the regulator agreed Environmental Limit Values (ELV's) were met. This process had a multi analysis approach to allow for the many different variables which required to be controlled in tandem to meet the ELV's. Final environmental sign off from commissioning was achieved in July 2017 and even with the higher than anticipated usage and the legacy construction issues, the site continues to improve its performance and protect the receiving environment from process contaminant problems.

It was found that engagement with the regulator at an early stage and regular/informed updates, good baseline assessments, a solid understanding of stakeholder management issues and initial and ongoing biodiversity identification allowed the project to manage this very sensitive development in a very fragile and reactive ecosystem.

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