Environment Marine and Fisheries

Oil Leak in Milford Haven

This blog post provides a brief background to oil spills, the Pembroke Refinery, and information on the recent oil leak in the Milford Haven waterway.

24 January 2019

Darllenwch yr erthygl yma yn Gymraeg | Read this post in Welsh

This blog post provides a brief background to oil spills, the Pembroke Refinery, and information on the recent oil leak in the Milford Haven waterway.

On 3 January 2019 an oil leak was reported at the Pembroke Refinery jetty. The Pembrokeshire Coast National Park has exceptional environmental value for natural beauty and tourism. The Milford Haven waterway, within the national park, is one of the deepest natural harbours in the world and a busy shipping channel; trafficked by ferries, tankers and pleasure vessels.

Pembroke Refinery is situated within the waterway and was acquired by Valero, an independent petroleum refiner, in 2011. The refinery is one of the most complex in Western Europe, producing gasoline, diesel fuels, liquefied petroleum gas and petrochemical feedstock, with total throughput capacity of 270,000 barrels per day. It is a major national employer with over 500 employees and hundreds of contractors.

Initial estimates suggested up to 10,000 litres (2,200 gallons) of heavy fuel were released from fuel pipelines into the south side of the Milford Haven waterway. A visible slick in the waterway appeared and a small amount of oil came ashore. However, it is now understood that no more than 500 litres of oil have been released – a serious incident, but a negligible quantity in comparison to the 1996 Sea Empress spill.

Aerial Image of Pembroke Refinery and Milford Haven waterway.

The incident has required a multi-agency clean-up operation and the immediate closure of the jetty and shipping routes. Valero has been staffing and funding the clean-up while Natural Resources Wales (NRW), Pembrokeshire County Council and Pembrokeshire Coast National Park monitor the area and advise. The response involved recovery at sea, beach clean-up where necessary, boom deployment to protect salt marshes and habitats and the use of drones to monitor the oil’s spread. This contained the oil so clean-up operations have been scaled down and shipping routes have since reopened.

Two fuel pipelines on the jetty were identified as the sources of the pollution incidents which affected surrounding water, land and wildlife in December and early January. Natural Resources Wales (NRW), issued an enforcement notice on 8 January to suspend the use of these pipelines until it is satisfied that their use will not threaten the environment.

Despite the limited release of oil, the environmental impact is yet to be gauged. The waterway is home to a variety of marine wildlife and sensitive seabed habitats. Beach surveys and seabed assessments are currently underway. An investigation into how the incident occurred is also ongoing and NRW and local authorities continue to monitor the area.

People – especially dog owners – are urged to be vigilant and watch for pollution on the coastline. They are asked to avoid oil if they discover it and to contact the NRW incident hotline: 03000 65 3000.

The Welsh Government Minister for Environment, Energy and Rural Affairs, Lesley Griffiths issued written statements providing updates on the current situation and the multi-agency response on 10 January and 17 January 2019.

The impact of oil

Oil is vital to modern economies due to its use in energy, transport and manufacturing. Today, global oil demand is approximately 100 million barrels per day (~15.9 billion litres).

Oil is typically transported vast distances from source to consumer, with 10 – 15 transfers between transport modes. Improvements in technologies, operating procedures and regulations have reduced spillage rates over recent decades. However, with such widespread usage and transportation, spills are inevitable. It is estimated that 30 – 50 per cent of spills are caused by human error while 20 – 40 per cent are caused by equipment failure. However, the vast majority of oil released into the environment is due to shipping and industrial activities, not spills or leaks.

The environmental impact of an oil spill is determined by far more than its size. When oil enters a marine environment it spreads with wind and currents, undergoing numerous chemical and physical changes. These processes, known as weathering, can either encourage oil to be persistent or to breakdown naturally, depending on weather and sea conditions, and oil quantity, type and spillage rate.

The long-term environmental impacts depend on many additional factors; including the type and location of ports and beaches, the oil sensitivity and ecological significance of local species, and selected clean-up processes. Marine ecosystems have high natural variability – it is difficult to know exact pre-spill conditions or identify definite points of recovery. Each ecosystem and location is unique – no two oil spills are the same.

The University of Delaware Sea Grant Program outlines common clean-up responses – with appropriate responses dependent on each individual case. Near shorelines, booms (floating barriers) can contain oil while skimmer equipment removes it from the water surface. Dispersants and biological agents also accelerate natural biodegradation. In some cases, the best method is to leave the oil to disperse by natural means.

Remembering the Sea Empress Oil Spill, 1996

On 15 February 1996, the Sea Empress, a tanker carrying 130,000 tonnes of Forties Blend North Sea crude oil struck rocks entering the Milford Haven waterway just four miles from the refinery’s jetty. The tanker sustained serious damage, grounding and re-floating several times as attempts to control it and offload the oil were scuppered by heavy weather. 72,000 tonnes (~80 million litres) of a light crude oil were spilled into waters over 7 days, contaminating 200km of coastline. It became the UK’s third largest oil spillage and the twelfth largest in the world at that time.

The clean-up operation involved dispersants, around 100 skimmers and transfer pumps, 6km of offshore and 11km of inshore booms and assistance from French and Dutch vessels. At the height of the operation, over 50 vessels, 19 aircraft, 25 organisations and over 250 staff at sea and 950 on the shoreline were involved. The total clean-up continued for 18 months with estimated costs of £23 million. There were fears that oil contamination would have lasting implications for the fishing industry and tourism; in 1995 tourists spent an estimated £160m in the area.

Environmental impacts were severe, and included; 7000 oiled or dead birds being collected on shorelines, unknown numbers dying at sea and starfish, mollusc and limpet populations being almost entirely wiped out, causing seaweeds and algae which fed such animals to thrive. In the face of depleted populations, the cushion-star (Asterina Phylactica) began to fertilise itself, increasing its vulnerability with genetic implications of inter-breeding. Such alterations to marine ecosystems can have unforeseen ecological impacts. To protect from potentially contaminated produce, a temporary ban was imposed on commercial fishing – affecting the livelihoods of around 700 local people.

While the impacts were far-reaching, they were significantly minimised by a combination of factors. Tests showed that about 40 per cent of the oil, including many toxic components, evaporated rapidly after release. Wind directions carried oil away from the Pembrokeshire coast, enabling use of dispersants and 50 per cent of oil to disperse in the water column. The incident also occurred during the low-season for tourism and just weeks before thousands of migratory birds were due to return to the area. Although wildlife populations were damaged (to varying degrees), the great majority proved resilient and regained their former abundance.  

The UK Government appointed an independent committee; the Sea Empress Environmental Evaluation Committee (SEEEC) to assess the impact of the spill. Its principal findings and recommendations were published in the SEEEC report.


Article by Robert Byrne, Senedd Research, National Assembly for Wales

The Research Service acknowledges the parliamentary fellowship provided to Robert Byrne by the Engineering and Physical Sciences Research Council which enabled this Research Briefing to be completed.

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