In the immediate aftermath of a marine oil spill, the media is glutted with heartbreaking images of doomed animals and aerial shots depicting terrifying (yet visually striking) slicks of oil streaking the sea. These compelling images of environmental degradation receive the lion’s share of attention, but there’s another, equally important though less reported environmental issue related to oil spills: waste. Pictures of piled bags of contaminated waste might not be so prevalent, but the images and – more importantly – the waste are out there.

An independent team of scientists estimated that the most recent major spill, the blowout of BP’s Deepwater Horizon well in the Gulf of Mexico, resulted in 4.4 million barrels of oil being released into the environment. While scientists are baffled as to where most of it has gone (and, indeed, what impact it will have), some of it was collected by skimmers and booms or washed up on shore, resulting in over 640,000 barrels of liquid waste and more than 60,000 tonnes of solid waste (as of 19 September, at which point most cleanup activities had been completed). So, what happened to it?

According to Ken Haldin, Director of Communications for Waste Management, the company responsible for disposal of waste collected along the coasts of Mississippi, Alabama and the Florida Panhandle: “Collection of the oily waste in liquid form was one of the source reduction imperatives – if you can remove it from the water before it reaches the shoreline, you have an opportunity to separate the oil and to beneficially use a significant amount of oily liquid.” Of the liquid waste, 343,663 barrels were oil and water mixtures or emulsions from which oil could often be recovered – predominantly through centrifuging – and sold on either as crude feedstock or for fuels blending. The water underwent treatment before either being discharged to a sewage treatment plant or pumped into a deep injection well, a common practice with wastewater disposal.

When the oil actually made it to the shore, solid wastes posed more of a problem. Waste Management’s ‘Waste Management Plan for Mississippi, Alabama and Florida’ explicitly states: ‘Initially, the primary effort will be to collect, contain and remove contaminated materials as quickly as possible… As time progresses with spill cleanup activities and understanding of the waste being generated is attained, reuse and recycling of the waste will become more feasible.’ This focus on speed (a practice known as ‘dig and dump’) meant that most of the oil-contaminated solid waste initially headed straight for landfill or, occasionally, incinerators. BP collected nearly 55,000 tonnes of contaminated sand, debris, vegetation, irreparable boom, protective clothing and so on, in addition to 8,074 tonnes of non-contaminated solid waste and just 203.6 tonnes of ‘recyclables and recoverables’. According to the Associated Press, nine Gulf Coast landfills had received over 50,000 tonnes of oily debris and boom by mid-August. These were normal municipal landfills (oil spill waste was not classed as hazardous), three of which were already being investigated for potential environmental violations.

At the beginning of the cleanup process, a great bulk of the waste was contaminated sand, some of which was segregated at the landfills for potential cleaning or reuse by asphalt companies, for example. As the cleanup progressed, techniques became more refined (as the plan suggested they would) and, according to Haldin, the amount of sand collected “declined significantly as they changed procedures at the shoreline – using sifting instead of shovelling tools and different instructions for the cleanup crews”.

While this is the largest oil spill in American history, it may not be the worst as it occurred a mile deep, 50 miles from shore in warm waters. The water temperature is significant as the microorganisms that naturally break down oil thrive in warmer seas and the depth and distance from shore are significant because they (along with 1.8 million gallons of extremely controversial chemical dispersants) prevented most of the oil from reaching the shore and making a mess.
A much smaller spill closer to land, by contrast, can create a great deal of waste. In December 1999, the Erika oil tanker sank about 30 miles from France’s Brittany coast. The tanker split in half and came to a rest less than a tenth of a mile below the surface of the water, releasing between 10,000 and 20,000 tonnes of heavy fuel oil into rough seas. Stormy weather meant little oil could be collected at sea and it was widely dispersed before currents and the tide brought it ashore (even in good weather, booms and skimmers can only remove a small proportion of a large spill at sea – the International Tanker Owners Pollution Federation estimates just 10 to 15 per cent can be captured at best – and even these figures plummet in rough conditions). The Deepwater Horizon spill was 200 to 450 times larger than the Erika, but the smaller accident ultimately resulted in 260,000 tonnes of solid waste, compared to 60,000 in the Gulf.

Managing – from collection to treatment – all the waste that accumulated on the French coast was a monumental task that took nearly three years and involved a purpose-built treatment facility. Oily waste (as in the Gulf, mainly sand, but also seaweed, pebbles, debris, tools, boots and clothes) was initially stored in 33 intermediate sites – large holes lined with plastic membranes that were excavated close to beaches – before being transported to one of four heavy storage sites. Most of the waste was eventually washed with cold diesel oil and the sand then separated from the oil through vigorous cold water washings and a hydrocyclone unit, which uses centrifugal force to separate particles of different densities. The cleaned material was eventually sold on as road material or mixed with cement to make concrete. As for the larger waste items, which could not be cleaned in this way, they were first crushed, then washed with diesel to reduce the oil content and finally pyrolysed at 600°C to produce coke for cement kilns. After washing, the fuel oil itself was largely recovered by separating it from the diesel for use as oil refinery fuel.Here in the UK, oil spills requiring specialist cleanup efforts occur all the time, though most are obviously not of the headline-grabbing variety. Mark Gillingham of Briggs Environmental Services, one of more than 80 spill contractors in the UK, estimates that his company alone deals with about 12 spills a week. Briggs looks after between 250 and 300 ports in the UK and responds to spills of anything more than 20 litres. Cleanup efforts in ports and harbours employ similar techniques to those further out to sea – booms and skimmers – which tend to be more efficient in still waters, though Gillingham notes: “If the situation is one where there’s bad weather and let’s say the docks are tidal or there’s a river running through them, then the possibility of losing oil is greater.” The oil that is recovered is separated from the water by centrifugation or heat treatment and, once it’s determined to be (mainly) free of contaminants, can be put back on the market, though according to Gillingham: “You wouldn’t put a recovered oil into your Mercedes, but you might use it in your boiler.”

The waste that results from these smaller spills tends to be quite similar to waste from larger spills: contaminated absorbent materials (absorbent booms can only be used on one spill because “they’re contaminated with a particular kind of waste, so they become waste themselves”), weathered hard booms (which can be used on multiple spills, but don’t fare well in rough weather), contaminated packaging, personal protective equipment, and – in the case of beach cleanups – oiled sand and vegetation. Unlike in the US, though, this can’t usually be landfilled due to EU Landfill Regulations; Gillingham says: “You can’t landfill anything that is more than six per cent organic carbon. So, by definition, oils are 100 per cent organic carbon, so even if you’ve got soil and sand, as soon as you get over the six per cent level, you can’t landfill it.” Instead, the UK’s “fairly strict regulatory regime” ensures that “if it’s recoverable, generally it always will be recovered”: oil is recovered from absorbent materials through centrifugation or presses and from sand through washing with water (as oil and water don’t mix) or by applying natural solvents or detergents if oil sticks to the sand. While the absorbent material can be reused as simple cleanup rags, much of the resulting waste is incinerated or, in the case of contaminated materials, landfilled (so long as it’s not too contaminated, that is).
Briggs also deals with land-based spills and these, in fact, make up the bulk of the company’s workload: it only deals with about two spills a week in the marine environment, while it handles 10 or more land-based spills in the same time frame. Oil spills on land tend to have fewer far-reaching consequences, though, as the oil does not spread over large areas. For simple spills on tarmac, Briggs seals drains, places absorbents in the area, and squeegee sweeps the oil up. For spills in soil, the company often digs up the soil and takes it for washing – where the oil is removed by a process of particle size separation as the oil will stick only to certain grain sizes – or for bioremediation – where bugs are used to break down the oil. And for spills where the oil gets into rivers, Briggs often booms the river off, puts absorbents at strategic points or even cuts trenches to collect the oil.

Doubtless in these situations, some oil remains in the environment, and in fact, Gillingham says, one of the most common sources of land-based leaks is difficult to staunch: “Electric companies transport electricity in cables which contain oil to keep them cool, and it’s not uncommon for them to spring a leak. Because it’s a complex situation there, the leak may go on for ages because you can’t cut off the electricity supply, so you can have several tonnes leak into the environment.” Asked if we should be worried about this, Gillingham says no – because these cables tend not to be placed near underground rivers or boreholes and because “the environment has a huge capacity for breaking down contaminants, and oils are really natural products”.

Nonetheless, people are worried about some sorts of spills, and well they should be as companies are increasingly drilling for black gold in places where nature, let alone humans, would have trouble cleaning up oil. In contrast to the US and most of the EU, which want to wait for the results of independent reports into the Gulf spill before pressing ahead with deep sea drilling, the UK government recently gave Chevron permission to drill for oil off the coast of Shetland in the North Atlantic. Even more worryingly, the government of Greenland, keen for financial independence from Denmark, seems similarly determined to open its waters to oil companies – Scottish energy company Cairn is already looking for oil in the Arctic waters there and more drilling licenses are expected soon.

These developments are worrying for many reasons, not least of which is that cleaning up an oil spill in cold waters would be incredibly difficult. Oil becomes more viscous and dissipates more slowly at low temperatures and the natural microorganisms that break it down don’t function well in cold water. What’s more, Arctic drilling can only take place in the summer in the absence of sea ice (though global warming is extending the drilling season), so completing a relief well, the likes of which finally ended the flow of oil in the Gulf, could take several years. But that’s not the only hazard ice poses; according to the National Environmental Institute of Denmark, ‘oil can adhere to ice or be trapped in freshly formed ice and then transported over large distances’. And oil trapped under ice is almost always impossible to detect; according to a 2009 report by the WWF, even ground penetration radar ‘cannot detect thin oil slicks or oil trapped under new ice, young ice, first year ice, rafted ice, rubbles or ridges, or ice thicker than seven inches’. Ice, especially moving ice or large icebergs, and severe weather conditions, including high winds and low visibility, would also hamper traditional cleanup operations – the ubiquitous booms and skimmers would be rendered even more inefficient.

With no way to efficiently get at or collect oil, there would be little waste in such a spill, of course, and so perhaps the fact that there was so much solid waste from the Deepwater Horizon and other oil spills isn’t such a bad thing after all: even more devastating would be a spill from which there’s no waste to recover...