Polluting Wrecks in the Baltic Sea

Abstract

The Baltic Sea is a shallow inland sea on the continental shelf of northern Europe (Fig. 7.1). The shores and bottoms in the area of Sweden, Finland, Russia and Estonia are mainly rocky with skerries, while the shores and bottoms in the area of Latvia, Lithuania, the enclave of Königsberg (Russia), Poland, Germany and Denmark are mostly flat and sandy with sand, clay and silt bottoms. Water exchange with the North Sea and the Atlantic Ocean is mainly through the shallow Danish Straits, Kattegat and Skagerak, resulting in a salinity range of 2–12‰ due to intermixing from riverine input. The area of the Baltic Sea is 392,979 km², the water volume is 21,721 km³ and the average depth is 52.3 m with a maximum depth of 459 m.

7.1 Introduction

The Baltic Sea is a shallow inland sea on the continental shelf of northern Europe. The shores and bottoms in the area of Sweden, Finland, Russia and Estonia are mainly rocky with skerries, while the shores and bottoms in the area of Latvia, Lithuania, the enclave of Königsberg (Russia), Poland, Germany and Denmark are mostly flat and sandy with sand, clay and silt bottoms. Water exchange with the North Sea and the Atlantic Ocean is mainly through the shallow Danish Straits, Kattegat and Skagerak, resulting in a salinity range of 2–12‰ due to intermixing from riverine input. The area of the Baltic Sea is 392,979 km², the water volume is 21,721 km³ and the average depth is 52.3 m with a maximum depth of 459 m (Baltic Sea, 2023).

Fig. 7.1

From left. Lazaretschiffe C (S/S Stuttgart) (German National Archive), Multibeam sonar map of the wreck of S/S Stuttgart (Hac B., Maritime institute in Gdansk 2016), Samples of the soil taken in the area of the wreck using a VanVeen sampler and a vibrocorrer (Hac B., Maritime institute in Gdansk 2016)

Tidal fluctuations average between 3 and 24 cm. There are seiches (max. 30 cm) and water level changes due to wind (max. 200 cm). The sea is often turbulent and can create waves that are short and steep. The maximum recorded wave height was 14 m (24.12.2004) with a wave length of 50 m. The Baltic Sea is a particularly sensitive area to pollution from fuels, oils, and chemicals such as fertilisers, sewage and substances from dumped chemical and conventional munitions. These inputs into the marine system are compounded due to the very low exchange of the Baltic Sea with the Atlantic Ocean because of the narrow outflows, and the residence time can be 25–30 years; this results in a low capacity of the basin to self-purify and flush pollutants and contaminants from the system. Therefore, pollution from sunken ships in the Baltic Sea poses a significant threat to the ecosystem.

7.2 History of Operations

As of 2005, there were an estimated 8569 potentially polluting shipwrecks in the world’s oceans, of which 1583 were oil tankers. Approximately 75 percent of these wrecks sank during the Second World War. More than 70 years later, these wrecks are a major source of potential pollution and represent a global marine pollution risk (Michel et al., 2005). The wrecks on the bottom of the Baltic Sea, containing heavy and light fuel oil, represent merchant and naval vessels from the period of both World Wars, as well as vessels sunk in the twentieth and twenty-first centuries as a result of collisions or storms that have occurred since the wars.

The Gulf of Finland, the Gulf of Riga and its approaches, the Gulf of Gdansk and the southern Baltic Sea, as well as narrow areas such as the Danish Straits and the approaches to the Kiel Canal, saw particularly intense warfare in which many ships and other liquid-fueled vessels were sunk. In just one operation, the evacuation of troops and civilians during Operation Hannibal by the German Kriegsmarine in 1945, some 250 vessels were sunk, many of them carrying large quantities of fuel. In total, it is estimated that there are around 1000 wrecks in the Baltic Sea alone, some with unspecified, sometimes significant quantities of fuel (for their own use as well as cargo) in their holds or tanks.

Scientific institutions (IMUMG—Maritime Institute of Maritime University of Gdynia, IOPAS—Institute of Oceanology Polish Academy of Science, SYKE—Finnish Environment Institute) and the maritime administrations of the Baltic States are still investigating what percentage of the wrecks are dangerous for the environment. Given the passage of time and the progressive corrosion of the wrecks (steel loss of about 0.01 to 0.1 mm/year), the risk of major spills and pollution of the waters and beaches of the Baltic Sea is rapidly increasing (Pärt et al., 2015). Time, anthropogenic activities in the water such as fishing, stormy weather in shallow areas and hull degradation due to corrosion, all significantly increase the possibility of large spills. Currently, large spills from wrecks are occasionally recorded, but small spills or leaks from these wrecks are common.

Periodically, large slicks of fuel appear in the open sea, the origin of which is difficult or impossible to determine. Very often these are likely leaks from wrecks. The use of VTS (Vessel Traffic Services) in busy areas and AIS (Automatic Identification System) throughout the Baltic Sea has meant that uncontrolled discharges of fuel from active vessels have been stopped and, if they do occur, the offender can be found within a matter of hours. Due to the small area of the Baltic Sea, each piece of its seabed has a clearly defined ownership. The areas of responsibility of the individual countries overlap and cover the entire area of the sea.

7.3 Wrecks in the Baltic Region

Sweden, Finland, Russia, Estonia, Lithuania, Poland, Germany and Denmark maintain their own services to identify potential pollution hazards. The knowledge of the subject, the capabilities and modus operandi, and the institutions monitoring the situation vary greatly and are at very different levels of organisation and technical sophistication.

7.4 Sweden

The Swedish National Maritime Museums maintains a catalogue of data on 17,000 underwater objects in its waters. This catalogue has now been integrated into the FMIS (Informationssystemet över fornminnen) and the Historic Sites Information System. It has been estimated that 316 wrecks may have some fuel resources, but only 31 wrecks pose a significant threat to the environment (Sjöfartsverket, 2014). These are Cat 1 wrecks containing more than 100 tonnes of fuel. At the same time, there are ongoing efforts in Sweden to clean up the wrecks that have been identified as hazardous.

To this end, Chalmers University has developed the VRAKA assessment system, and the Swedish Maritime and Water Administration effectively cleans up 2 or 3 wrecks per year. To do this, it has a fixed annual budget of 2.4 million euros allocated in advance for 10 years. This makes it possible to establish a sustainable system for planning, monitoring and removing dangerous wrecks.

A good example of this is the wreck of the ship Skytteren, which sank on 1 April 1942 about 10 km off the west coast of Sweden near the town of Lysekil in the Kattegat (VRAK Museum of wrecks, 2023). During an attempt to break a naval blockade, the ship was damaged by the Germans. To prevent the Germans from seizing the valuable cargo of Swedish steel and ball bearings, the captain decided to sink the ship. According to the environmental risk assessment, Skytteren is number one on the list of the 30 most environmentally hazardous wrecks. It is estimated that the wreck may contain up to 400 cubic metres of oil. The location of the wreck is already outside the Baltic Sea proper, but in the main strait leading into the Baltic, which means that it is an excellent example of coordinated action by the Swedish services as a case study for oil clean-up operations at greater depths (74 m).

According to the Swedish website Vrak Museum of Wrecks, ‘In the winter of 2005, large quantities of oil appeared in the waters north of Måseskär on the west coast of Sweden. The oil came from Skytteren and at its peak the discharge was almost 400 litres per day.’ The Skytteren spill was a wake-up call to a problem that had previously been overlooked.

By 2018, work had begun to remove environmentally hazardous substances from Skytteren. After extensive investigations in 2021 and 2022, 175,000 L were recovered by drilling holes in the hull and pumping out the oil and oil-water mixture. However, the wreck may still contain oil because Skytteren is on its side and some of the fuel tanks are inaccessible.

7.5 Finland

Finland has an interactive database, produced by SYKE, the Finnish Environmental Institute, showing the distribution of known wrecks (Finnish Wreck Base, 2023), with 5200 records, of which about 1000 are wrecks, of which 420 wrecks contain fuel, and of those, 12 are Cat. 1 wrecks (more than 100 tonnes with certainty), 24 are Cat. 2 wrecks that may contain more than 100 tonnes (with less certainty), 68 are Cat. 3 wrecks expected to contain between 10 and 100 tonnes of fuel and could be considered potentially hazardous, and the remainder contain less than 10 tonnes (Rytkönen, 1999, Jolma, 2009). As of 2019, the concept for the operation of the base has changed. The search, survey and clean-up of the wrecks is carried out by the Ministry of the Environment, the Finnish Coast Guard and the Finnish Navy in cooperation with SYKE. These institutions have been continuously provided with financial and material resources (ship Aranda) to carry out wreck exploration and clearance operations.

7.6 Russia

There are large amounts of wreckage, including potentially environmentally hazardous wrecks, in both the Gulf of Finland and the Königsberg enclave areas of western Russia. This is a result of the wars that took place in the area of both locations. Based on historical literature, it can be estimated that there are at least several hundred such wrecks. Unfortunately, there is no access to the official wreck database of the Russian Hydrographic Office. The only visible fact that such knowledge exists in Russia are the positions of known wrecks marked on nautical charts (both Russian, Finnish, Polish and English). These charts do not define the size or nature of the wrecks, other than that they are dangerous to navigation. It is therefore difficult to estimate how many of them are potentially hazardous to the marine environment. Preliminary data collected by J. Rytkönen (2021) for the study for the HELCOM Submerged project indicate a high potential for oil pollution in the eastern Gulf of Finland, which is in Russian territorial waters. Private divers report that the following wrecks lie in the Russian part of the Gulf of Finland: 7 destroyers (300–500 tonnes of oil), several minesweepers and large submarine chasers (up to 100 tonnes of fuel), 8 submarines (60–120 tonnes of fuel), 4 minesweepers and gunboats (30–100 tonnes of fuel), 3 large merchant ships (with possibly hundreds of tonnes of fuel), and a bunker tanker (1000 tonnes of petrol). It is thought that the 35 known wrecks may contain some 843 tonnes of light fuel oil and 5870 tonnes of heavy fuel oil. How much of this fuel remains in the tanks 80 years after sinking is entirely unknown.

7.7 Estonia

As a result of fierce naval battles and difficult navigational conditions, there are many wrecks in Estonian waters. According to Estonian sources, about 705 wrecks have been located (SHIPWHER, 2010), of which 54 have been identified as potentially polluting, and 13 of these have been investigated in detail. Wrecks are registered in the central wreck register SHIPWHER, which is available online. The Estonian Maritime Administration is responsible for investigating wrecks and must remove those that pose a safety or environmental risk. The Estonian Maritime Administration is also responsible for mapping and registering wrecks along the waterways (Svensson, 2010). The database currently contains 1297 objects on the seabed. In July 2023, it was reported that the wreck of HMS Kasandra, which sank west of the large Estonian island of Saaremaa after the First World War, had been found (The Baltic Times, 2023). The Climate Ministry reported that, ‘The ship is thought to have carried around 780 tonnes of fuel, some of which was probably in the ship the time of the sinking. Given the relative integrity and condition of the wreck, it is believed that most of the fuel remains trapped within the wreck.’

7.8 Latvia

There is no access to an official shipwreck database of Latvia, which is presumably held by the Latvian Maritime Administration (Svensson, 2010), which ensures safe navigation in its waters. Experts from the Ministry of the Environment reported in 2010 that there had been cases of assessment and removal of shipwreck contamination, but these concerned recently sunken ships in port areas. No visible contamination was found in other areas. The unofficial register of shipwrecks in Latvia, maintained by the private association of divers ‘Nirēju klubs Daivings’, lists about 200 wrecks in Latvian waters. There are at least a few wrecks from the First World War, which gives them the status of archaeological heritage. Most of them are steamships, but some of them pose a certain environmental risk due to the armaments and shells on board. An unspecified number of ships and vessels sunk during World War II contain wrecks that may pose an environmental risk.

7.9 Lithuania

There is no official information on the number of wrecks in Lithuanian waters. Recently it was reported that there are only seven, which is fewer than expected due to the historical conditions and war losses in this area during World War II. Interestingly, on the Polish map ‘Wraki Bałtyku’, a private Polish company that organises wreck diving, there are ten locations of large wrecks of interest to divers that lie close to the Lithuanian coast. The Maritime Safety Administration is the only institution capable of conducting wreck surveys, as it is the only one with hydrographic survey vessels equipped to conduct underwater surveys (Svensson, 2010). Recent small spills recorded on the surface suggest that there are several wrecks on the seabed that contain some fuel and are leaking. There is no information on ongoing clean-up operations or monitoring of dangerous wrecks.

7.10 Poland

The official database of wrecks in Poland is maintained by the Hydrographic Office of the Polish Navy (Database of Underwater Objects—BDoP) and contains several thousand records (in 2023—total 10,502), including about 530 wrecks (June 2023). Experts believe that there are more, in the range of 600 to 800, many of which have not yet been found or identified. A project to assess the environmental conditions of the seabed in parts of the Polish Exclusive Economic Zone (EEZ) is currently underway on behalf of the Chief Inspectorate for Environmental Protection (GIOS); at this stage, surveys have been carried out in up to 30 percent of the EEZ and will continue up to about 70 percent of the EEZ. Several dozen new wrecks are discovered each year (in 2023–43 wrecks and 808 objects). Previously, wrecks and information were collected by the Maritime Institute in Gdansk (IMG) and the Institute of Oceanology of the Polish Academy of Sciences (IOPAS in Sopot). After the takeover of the Maritime Institute in Gdansk by the Maritime University in Gdynia, IOPAS took over the management of the wreck projects, but their interest has become more focused on biological research.

According to IMG’s earlier assessment, about 18 of the wrecks investigated are classified as Cat. 1 and 2 (≥100 tonnes of fuel, of which 2 are ultra-hazardous, i.e., Stuttgart and Franken), and about 50 are Cat. 3 wrecks (10–100 tonnes). The remainder are likely to be Cat. 0, i.e., not hazardous to the environment. At present, the maritime administration has no planned measures to prevent pollution, no wrecks have been cleaned up to date and ongoing surface pollution is dealt with by SAR (Search and Rescue). Some of the more dangerous wrecks have been given special protection due to the high number of casualties from the Second World War. There is ample evidence that these wrecks may have large quantities of oil in their tanks. However, due to the sensitivity of the work on the so-called wet graves (e.g., Wilhelm Gustloff 10,000 victims, Goya about 5000 victims, Steuben about 6000 victims), the start of detailed investigations has been postponed. There are currently no plans for hazard identification on these wrecks.

7.11 Germany

The official database of underwater objects, including wrecks in German waters, is maintained by the Federal Maritime and Hydrographic Agency (BSH) and contains approximately 2500 objects (Svensson, 2010). This information is mainly used for maritime safety (Bundesamt, 2023). Objects such as large rocks, containers and others are also included in the database. The Wikipedia wreck list currently lists 24 wrecks in German waters, most of which are warships and submarines from the Second World War. Although most of the wrecks are on the North Sea side, there are also wrecks near Kiel, Trawemünde and Warnemünde. The wreck map published by the BSH suggests that there are many more wrecks. This is also suggested by the nautical charts published by the BSH, which show the position of dozens of wrecks in the western Baltic Sea. There is a lack of information on current activities to review the status of wrecks and their environmental impact and potential danger. In Germany, which is a federal state, the coastal state is responsible for assessing and dealing with wrecks. In the Western Baltic these are Mecklenburg-Western Pomerania and Schleswig-Holstein.

7.12 Denmark

The Danish Maritime Safety Authority (DMSA) maintains a database of known wrecks in Danish waters. The purpose of the database is to maintain the safety of navigation. There are 2518 known wrecks in the register. For 90% of the wrecks registered before 2000, the data contains only information on the safe depth above the wreck, the depth around the wreck and the position. About a third of the wrecks described in the database are located in the waters of the Baltic Sea and the Danish Straits. The wreck register data is stored in an object class in the ESRI ArcGIS geodatabase. The data and documentation are in Danish. One major wreck removal operation is known, which is of the wreck of the Fu Shan Hai, sunk in 2003. In total, approximately 1500 tonnes of heavy fuel oil, light fuel oil and 35 tonnes of lubricating oil were recovered from the wreck or collected from the surface. In 2013, 620 m³ of water/oil mixture and 251 m³ of fuel were recovered from the wreck during a 50-day hot tapping clean-up operation. A detailed description of the salvage operations can be found in (Danish Navy, 2013) and (Mortensen & Rasmussen, 2013).

7.13 Wreck Risk Assessment Methods

There are several centres in the Baltic Sea region that use different methods to assess the risk of marine pollution from potentially hazardous wrecks. The most commonly used method is the Swedish VRAKA, recognised by the Swedish, Finnish and Polish representatives in Helcom Submerged. Other EU-related methods include the DEEPP project risk indicator method developed in the EU-funded SWERA project and the NOAA RULET risk methods. The HELCOM Submerged work proposed a risk approach similar to that used in the US. Poland has also developed its own for English E-DBA risk model protocol, which appears to be the most appropriate to adapt for the assessment of Polish wrecks. This method has a clear and simple structure, but does not take into account the change in risk level over time. However, it provides an unbiased risk assessment and identification of the most appropriate management strategy, thus minimising conflicts of interest with the Maritime Administration, which would be consulted throughout the assessment process (Hac & Sarna, 2021). The Finnish method is characterised by moving away from ‘risk assessment’ and focusing on factors that determine how easy or difficult it may be in a given case to remove fuel tanks from a wreck. When assessing individual centres, it is important that operations are optimised for the local conditions in which they operate (Table 7.1).

Table 7.1 Summary of shipwreck clean-up operations carried out in the Baltic Sea area

7.14 Case Studies of the Stuttgart and Franken Wrecks

7.14.1 SS Stuttgart

The wreck of the hospital ship SS Stuttgart lies on the bottom of the Gulf of Gdansk at a depth of 22 m, approximately 4.4 km northeast of the approach to the Port of Gdynia (Fig. 7.1). SS Stuttgart was built in 1923 at the Vulcan—Werke Hamburg und Stettin AG shipyard in Szczecin. From 1930, SS Stuttgart sailed on the Far Eastern Lines. With war looming, the ship was conscripted into the German Navy and converted into a hospital ship, known as Lazaretschiff ‘C’.

Fig. 7.2

Range of bottom contamination of 1050 bottom samples taken around wreck of S/S Stuttgart (Hac B., Maritime Institute in Gdansk 2016)

The ship’s fate was sealed in 1943 during the raid on Gdynia, which as a shipyard and naval port became a target for Allied air strikes. The air raid took place on 9 October 1943 when, among other things, the hospital ship Stuttgart was bombed, which for unknown reasons had been covered with camouflage netting and was not recognised as a hospital ship. The ship was carrying a large number of wounded soldiers from the Eastern Front. The number of wounded is still not known. Almost all of them perished in the flames. It is estimated that around 700 people died in the attack. The burning Stuttgart posed such a serious danger to other ships in the harbour that it was towed to the roadstead in Gdynia and deliberately sunk with the bodies of the victims. This operation was carried out by the guards of the third escort flotilla using 25 88-mm shells.

An attempt was made in 1950 to develop a method of raising the wreck from the seabed. Due to a lack of suitable equipment and documentation, the attempt failed. In 1955, the Polish Salvage Commission gave its final verdict on the sunken wreck, based on the testimony of divers who had surveyed the wreck in 1952 and 1953. The Commission concluded that the hull was 80% damaged, while the wear on the machinery, due to its age and 10 years in the water, was estimated at 100%. The wreck of SS Stuttgart was considered an obstruction to navigation and removed by demolition using explosives. A pyrotechnic method was used for heavily damaged wrecks and to remove obstructions to navigation. The wreck was ripped apart with explosives and the parts were removed with cranes. Removal of the wreck began in 1957.

It should be noted that there is no report on the demolition of the wreck in terms of environmental impact. An undetermined amount of fuel leaked from the wreck’s tanks during the demolition. Surveys in the area of the wreck site in 2009 revealed significant scattering of ship remains on the seabed. This suggests that Stuttgart was scuttled, indicated by the hull, superstructures and the part of the hull that was accessible after the removal of any steel structures that managed to separate from the wreck. A multibeam echosounder survey on 9 May 2015 provided a detailed picture of the remains of the wreck on the seabed.

The Maritime Institute in Gdansk conducted a seabed survey around the wreck in an area of approximately 1.5 km². The survey was carried out using a multibeam echosounder, towed side-scan sonar and a sub-bottom profiler. A total of 1050 bottom and water samples were taken for chemical, toxicological and biological analysis using a Van Veen corer, and 50 sediment cores up to 3 m in length were taken using a vibracorer. An ROV visual inspection was also conducted.

In the area of the seabed surveyed, contamination of the seabed with synthetic heavy fuel oil from the Fisher-Tropsh process was detected (Hac, 2014). Contamination was found with a thickness ranging from 5 to 130 cm over an area of approximately 415,000 m² (Fig. 7.2). The levels of polycyclic hydrocarbons exceed standards by about 3000 times (Rogowska & Wolska, 2019). High levels of many heavy metals exceed the standard locally by up to 18,000 times. Locally, there are large lakes of liquid fuel deposited in the subsurface depressions. We estimate that about 600 to 1000 tonnes of synthetic fuel, which is heavier than water, is deposited on the seabed.

Fig. 7.3

From left. Supply Vessel Franken (Trossschiff ‘Franken’) (German National Archive), Loading plan of Supply Vessel Franken (Trossschiff ‘Franken’) (German National Archive) Multibeam sonar map of the wreck of S/V Franken (Hac B., Maritime institute in Gdansk 2016)

Several ideas were put to the Maritime Administration to solve the problem of soil contamination on the seabed. One was to remove the entire top layer of contaminated soil, clean it of oil and place it back on the seabed. This is not possible due to the size of the one million cubic metres of contaminated soil and regulations that prohibit the placement of contaminated soil on the seabed. The cost of this measure has been estimated at €150 million.

Another approach proposed was to cover the area with a special mineral-based, chemically neutral mixture that would allow the fuel-eating bacteria to develop and grow rapidly, creating favourable conditions for their growth and accelerating natural soil remediation. This is the most environmentally friendly method. The cost of the operation was estimated at around €15 million. Very detailed monitoring of the extent of contamination and changes in the soil over the past 8 years, its natural remediation capacity, is currently underway.

7.15 Supply Vessel Franken (Trossschiff Franken)

Franken was a 179-metre-long, motor-driven tanker/supply ship with a displacement of 22,850 tonnes, construction of which began in 1937 at the Deutsche Werke shipyard in Kiel (Fig. 7.3). The hull was launched on 8 March 1939. In 1942, it was towed to Burmeister & Wain in Copenhagen, where it was completed and commissioned on 17 March 1943.

Fig. 7.4

Steps to be taken from the discovery of the wreck, through its identification and risk assessment, to the removal of fuel from the wreck—Part I (Hac & Sarna, 2021)

It was used as a supply ship for the battleship Prinz Eugen and the ships of the armoured group Tiele, and also supplied torpedo boats and minesweepers. The ship was sunk on 8 April 1945 by the Soviet air force. The supply vessel was capable of carrying 9500 tonnes of fuel (heavy oil, light oil, aviation gasoline), 306 tonnes of lubricating oils of various types, 973 tonnes of ammunition (calibres from 20 mm to 280 mm), 822 m³ (790 tonnes) of spare parts, and technical supplies for ships.

The last information on the amount of fuel on board, which was intercepted by Allied intelligence 8 days before the sinking, was 3060 m³ of fuel. During these 8 days a considerable amount was transferred to other ships and an unspecified amount spilled on the surface when the bombed ship had broken. We estimate that between 600 and 1000 tonnes, mostly heavy fuel oil, remained in the surviving tanks. Investigations have shown that in the trough around the wreck, an area of about 3 hectares, the ground is saturated with a large amount of heavy fuel (Hac, 2018).

7.16 Conclusion

Because of their vulnerability to pollution in the Baltic Sea, the countries bordering the Baltic Sea have taken significant steps to assess the number of hazardous wrecks, including addressing how to assess the risk of oil spills, how to clean them up by removing the deposited fuel and how to rehabilitate the contaminated land around the wrecks. All Baltic countries cooperate in the oil spill clean-up system. Finland and Sweden have a good track record in cleaning up wrecks. Other countries have made progress in developing and implementing systems to locate and remove contamination from wrecks. There are activities under the European South Baltic Project and other projects that target the Baltic Sea as a region of particular environmental concern. A two-pronged effort is currently underway in Poland to clean up known wrecks that pose an environmental risk. On the one hand, through participation in the above-mentioned South Baltic projects, experiments are being carried out to introduce new methods of seabed remediation (the Stuttgart wreck) and full information is being obtained on 18 wrecks in the Polish EEZ (including the Franken wreck) suspected of containing various types of fuel. On the other hand, state institutions such as the Maritime Office have started to prepare the information needed to set up a fundraising system and to issue calls for tenders for the clean-up of wreck tanks. The first wrecks will be cleaned within the next 5 years. The attached algorithm shows how such an operation could be carried out (Figs. 7.4 and 7.5).

Fig. 7.5

Steps to be taken from the discovery of the wreck, through its identification and risk assessment, to the removal of fuel from the wreck—Part II (Hac & Sarna, 2021)