The Beatrice Field development presented particular challenges in the area of environmental protection. Planning and development consents were greatly dependent on the development of a viable and credible environmental protection plan. The overall plan was based on an impact study followed by baseline environmental studies which formed the basis for a continuing monitoring programme. The scope of this is summarised and the scope and extent of plans for pollution prevention and control described.

The Highland River Purification Board is carrying out a detailed study of the effect of Inverness sewage on the Beauly and Inverness Firths to ascertain the present degree of pollution and the best location for a new outfall. The survey comprises hydrographic work to identify the main currents in the Longman area, analysis of water and sewage quality and surveys of the littoral and sub-littoral fauna.

As part of the Moray Firth environmental monitoring programme Britoil has commissioned a series of studies on the mudflats in Nigg Bay commencing in 1981. These cover an area of about five square miles and are situated in the Cromarty Firth adjacent to the oil terminal that handles crude oil from the Beatrice Field.

Capillary gas liquid chromatography (GLC) analysis of the mudflat sediments in 1981 and 1982 showed a major autochthonous input of algal hydrocarbons as indicated by high n-C17 and C17 alkene concentrations. In addition there were low levels of petrogenic contamination, with concentrations of unresolved complex mixture (UCM), in general, being less than 10 ppm. These concentrations altered little between the two surveys during which time effluent discharge commenced from the oil terminal.

In many of the GLC traces the dominant feature was an homologous series of n-alkanes in a smooth envelope from n-C22 to n-C34 with a maximum concentration at c. n-C25. This unusual distribution of n-alkanes does not appear to be associated with the UCM seen in many samples and may therefore not be of petrogenic origin. Possible sources of these components include bacteria and the erosion of local organic-rich shales, a selection of which have been sampled and analysed. Gas chromatography–mass spectrometry (GLC/MS) has been used in attempt to further clarify the origin of these n-alkanes.

Data on hydrocarbon levels in sediments and waters of the Cromarty Firth are presented for samples collected during the period 1979–81. Use of this data as a baseline for subsequent studies on hydrocarbon levels in the firth is discussed. Data are presented on organic pollution of the firth by industrial and domestic wastes and on a chronic pollution incident involving polychlorinated biphenyls. In general, hydrocarbon levels are low and have remained low with increasing industrial expansion on the shores of the firth. Organic pollution is localised but significant. Pollution from polychlorinated biphenyls appears to be diminishing but requires further investigation.

Hydrocarbon analyses, using gas-liquid chromatography (GLC), have been conducted on benthic sediments from around the Beatrice A platform immediately after completion of the first well using low-toxicity oil-based drilling mud. These analyses, as expected, showed the major organic contaminant in the sediments to be fresh base oil from the drilling mud. It could be detected to a distance of 3 km from the platform in the direction of the prevailing currents.

A year later, after the completion of five additional wells using low-toxicity oil-based mud, a repeat survey showed the drilling mud base-oil could be detected in similar concentrations (by gravimetry) over the same spatial area. GLC analysis, however, showed that the base-oil had been severely biodegraded at many stations. The degree to which the n-alkanes had been biodegraded varied considerably between stations but appeared to be related to the distance from the platform and/or the total concentration of oil in the sediments. This has resulted in a discrete ring around the platform within which there was a rapid (and in many cases complete) loss of n-alkanes through biodegradation. Possible reasons for this phenomenon are discussed.