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Bunding, also called a bund wall, is a constructed retaining wall around storage "where potentially polluting substances are handled, processed or stored, for the purposes of containing any unintended escape of material from that area until such time as a remedial action can be taken." [1]
The term can also refer to dikes, but it is frequently used to describe liquid containment facilities that prevent leaks and spillage from tanks and pipes, though sometimes any barrier is referred to as bunding. Frequently, the liquids in these tanks and pipes are toxic, and bunding is used to prevent the liquid from causing damage (either by force or its chemistry). If a large tank has a catastrophic failure, the liquid alone can cause extensive damage. [2]
If built properly, bunding is large enough and strong enough to contain the contents of an entire tank, though regulations may require it to be up to a third larger. When multiple tanks share a bund, the capacity is based on the largest tank. One of the most common designs for large tanks is a concrete or masonry wall around the tank with a concrete floor. [3]
Concrete works very well for many liquids, but it is unsuitable for some applications like containing strong acids. Using earth berms for bunding is not recommended for most situations, though liners can be used to decrease permeability. Smaller tanks often use containers made of steel or plastic. The material used depends on cost, the chemical properties of the liquid and its density. Plastic tanks cannot hold very dense liquids at high wall levels. Large, exposed bunding will need a sump pump or some other system to remove precipitation, though it may also be used to transfer spilled liquid into another container. Rainwater must be treated if the liquid being stored is toxic because there may be small amounts of it surrounding the tank. [4]
The bund may have a roof to prevent precipitation from getting in, but steps must be taken to provide adequate ventilation when storing flammable liquids. If the wall is over a meter high, it may require a ladder or steps to allow people to escape quickly. Another design uses a channel that drains the liquid to a secondary container. [5]
When the risk of tank failure is not as likely or when it would not cause extensive damage, the bunding may be designed to merely contain small leaks from hoses and valves. This bunding may not be able to contain the entire volume of the tank. Plastic and steel are used, but another common method is making a hump or lip around the perimeter of a concrete floor. Some bunding is temporary, such as short-term chemical storage in the field. A hump or slope type bunding is helpful when vehicles need access to the area. There is also a type of bunding that compresses when a vehicle passes over and expands once it has passed.[ citation needed ]
Bunding is a legal requirement in many countries, particularly around tanks, storage vessels and other plants that contain liquids which may be dangerous or hazardous to the environment. [6] Particular examples which receive specific attention in the UK, the rest of Europe and the USA are oil and fuel storage tanks and transformers at electricity sub-stations which are filled with oil for cooling and insulation purposes. In the UK commercial installations exceeding 200 litres and domestic installations exceeding 2500 litres require a bunded tank to comply with Environment Agency 'control of pollution regulations'. [7]
It is reasonably easy to construct a "water-tight" bund around the base of a tank or vessel. A concrete base and a sealed wall of masonry, brickwork, concrete or even prefabricated steel provides the holding capacity [8]
Almost all regulations require a holding capacity of 110% of the largest tank within the bund or 25% of the total capacity of all the tanks within the bund, whichever is the greatest. In addition, further guidelines in some countries (e.g. the UK) recommend additional measures such as providing sufficient "freeboard" or height of wall above the maximum holding capacity to accommodate dynamic factors such as a surge in situations of major tank failure or storm-driven waves in larger bunds. As a rule (and unless specific local laws prevail) most operators work to the 25%/110% capacity guide. [9]
As noted above, electricity sub-station transformers contain significant amounts of oil. A 110 MVA transformer may have up to 40,000 litres of cooling/insulating oil contained within the body of the transformer and its associated coiling radiators and storage tanks. Unlike ordinary fuel storage tanks, these are complex structures, with a higher propensity for leakage of the oil. Using the UK as an example, as electricity industry privatization took place in the 1980s and 1990s the new electricity companies were made aware of their environmental responsibilities.[ citation needed ] Most area and national companies realised that they had several thousand transformers, many of which had been leaking into the ground below them for many years.[ citation needed ] The companies embarked on an upgrading programme involving the construction of "water-tight" bunds to retain any oil leakage and to prevent further pollution and contamination.[ citation needed ]
They immediately encountered the problem of water build-up from rain being retained by the now "water-tight" bund; the unwanted rain-water reduces the holding capacity of the bund. Once the water level reaches more than 10% of the holding capacity of the bund, it is no longer fit for purpose and the water must be removed. The water is also likely to be, at best, moderately contaminated with a small film of oil on the top of it or, at worst, substantially contaminated by a thick layer of oil. This is worse on older, leakier transformers. This also can apply to any oil storage tank[ citation needed ]
Oil floats on water and, if still clean enough to see through, has a different refractive index than the water below, making the oil/water interface difficult to judge. This makes manual pumping difficult and unsafe. Removing the entire contents for disposal as hazardous waste is expensive and environmentally unacceptable. However, in the UK at least, the latest regulations [10] require some formal method to be put in place for the removal of the rainwater. One of the systems recommended is an automatic pump system which is able to discriminate between oil and water. A good system should work continuously and automatically and must fail to safety (e.g. not pumping). It should also provide alarms for conditions such as high water (indicative of pump or system failure) and high oil to warn that action to skim off the waste oil should now be done. These automatic pump systems are usually referred to as "BundGuards".
In the UK, manmade earthwork structures are sometimes constructed around housing developments, especially near industrial sites. The mounds of earth with vegetation (normally shrubs and trees) diminish the noise from the industrial site. [11] The bunds then create a more natural landscape instead of thick or high barriers. They can be built in curved or sinuous forms, depending on the landscape. Bunds are also used to protect housing from noisy transport routes such as motorways and railways. [12]
Allegedly bunds can be used to hold rainwater in lightly sloping plains that have lost vegetation due to drought and overgrazing. According to this theory, semi-circular bunds will hold the rainwater giving it time to penetrate the soil and rehydrate the seeds in the ground. [13]
Bund wall failures have occurred in the UK, such as at Warrington, Cheshire in 1994. A polypropylene tank holding about 30 tonnes of 40% aqueous caustic soda sprang a leak about halfway down the main wall.[ citation needed ] The corrosive fluid jetted out over the bund wall, causing great damage to the surrounding factory and adjacent premises. The bunding at Buncefield also failed to contain petrol and fire fighting water after the initial explosion and subsequent fire. [14]
Bunded containment is generally not designed for tank boilover, because this would require to cover an enormous footprint, as clearly demonstrated by accidents such as the Tacoa disaster. It is therefore tantamount that boilover be prevented in the first place. [15]
Bunds will deteriorate over time (e.g. cracks may develop in concrete walls or reinforcement bars may corrode) or suffer damage (e.g. vehicle strikes) or modifications may have been made. To ensure that bunds continue to provide the necessary protection against leaks and spills, bunds should be assessed periodically to ensure that they continue to provide sufficient integrity (e.g. will not leak).
National and local regulations often specify the frequency and method of bund integrity assessment. In the UK, for sites licensed by the Environmental Agency, the integrity assessment is normally annually. In Ireland, for sites licensed by the EPA, the integrity assessment is normally every three years. The actual permit or license for the site will normally specify the assessment interval.
There are two assessment techniques in use, hydrostatic testing, and visual inspection. In certain circumstances, both techniques may be used.
The general principles of hydrostatic tests are described in. [16] These general steps consist of
A visual inspection requires that a competent person examine the bund to determine whether the bund, in their opinion, is in a suitable condition to retain the primary containment contents in case of a spill. The examination will include a visual inspection of the inner and outer walls and the bund base. In particular, joints in the walls and base will be examined and also where pipes penetrate bund walls. Any defects that are likely to cause a leak are noted.
The definition of a competent person may be defined in the permit but is generally considered to refer to a Chartered Engineer with appropriate experience [1]
Where there is doubt as to the integrity, then the visual inspection may be supplemented by a low-level hydrostatic test.
All new bunds should be tested before they enter service. Test methods are usually specified in the design code used to design the bunds. Two design codes have been historically used throughout the UK and Ireland, BS8007:1987 and CIRIA163. BS8007:1989 has now been withdrawn [17] and replaced by BS EN 1992-3:2006. [16] However, this withdrawn standard is still extensively referenced by many regulators and the testing requirements are identical in both standards. It is important that this testing is carried out before tanks, pumps or other equipment is placed in the bund. This is because tanks may try to float and thus become unstable and other equipment may be damaged by water immersion.
Prefabricated bunds will have generally been tested at the factory where they are made and therefore should be accompanied by a test certificate.
The guidance for assessment of existing bunds differs significantly between the UK and Ireland. In the UK, visual inspection for existing bunds is the preferred assessment method. [18] This is due to concerns re-tank stability and the possibility of promoting corrosion of the base of the tank. In Ireland, for site regulated by the EPA, hydrostatic testing is the preferred method unless there are safety or practical reasons why a hydrostatic test cannot be carried out [1]
Potential reasons as to why a hydrostatic test may be unsafe or impractical include
In some cases, it may be necessary to test joints and bund penetrations (such as by pipes) for watertightness using a limpet dam or similar. [19]
A pipeline is a system of pipes for long-distance transportation of a liquid or gas, typically to a market area for consumption. The latest data from 2014 gives a total of slightly less than 2,175,000 miles (3,500,000 km) of pipeline in 120 countries around the world. The United States had 65%, Russia had 8%, and Canada had 3%, thus 76% of all pipeline were in these three countries. The main attribute to pollution from pipelines is caused by corrosion and leakage
A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater (sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the treatment efficiency is only moderate. Septic tank systems are a type of simple onsite sewage facility. They can be used in areas that are not connected to a sewerage system, such as rural areas. The treated liquid effluent is commonly disposed in a septic drain field, which provides further treatment. Nonetheless, groundwater pollution may occur and is a problem.
A hydrostatic test is a way in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant. Strength is usually tested by measuring permanent deformation of the container.
A berm is a level space, shelf, or raised barrier separating areas in a vertical way, especially partway up a long slope. It can serve as a terrace road, track, path, a fortification line, a border/separation barrier for navigation, good drainage, industry, or other purposes.
A gas cylinder is a pressure vessel for storage and containment of gases at above atmospheric pressure. High-pressure gas cylinders are also called bottles. Inside the cylinder the stored contents may be in a state of compressed gas, vapor over liquid, supercritical fluid, or dissolved in a substrate material, depending on the physical characteristics of the contents. A typical gas cylinder design is elongated, standing upright on a flattened bottom end, with the valve and fitting at the top for connecting to the receiving apparatus.
Heating oil is any petroleum product or other oil used for heating; it is a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers use for home heating and in other buildings. Home heating oil is often abbreviated as HHO.
An underground storage tank (UST) is, according to United States federal regulations, a storage tank, including any underground piping connected to the tank, that has at least 10 percent of its volume underground.
A containment building is a reinforced steel, concrete or lead structure enclosing a nuclear reactor. It is designed, in any emergency, to contain the escape of radioactive steam or gas to a maximum pressure in the range of 275 to 550 kPa. The containment is the fourth and final barrier to radioactive release, the first being the fuel ceramic itself, the second being the metal fuel cladding tubes, the third being the reactor vessel and coolant system.
Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled wet transformers, some types of high-voltage capacitors, fluorescent lamp ballasts, and some types of high-voltage switches and circuit breakers. Its functions are to insulate, suppress corona discharge and arcing, and to serve as a coolant.
A leak is a way for fluid to escape a container or fluid-containing system, such as a tank or a ship's hull, through which the contents of the container can escape or outside matter can enter the container. Leaks are usually unintended and therefore undesired. The word leak usually refers to a gradual loss; a sudden loss is usually called a spill.
The Buncefield fire was a major fire at an oil storage facility that started at 06:01 UTC on Sunday 11 December 2005 at the Hertfordshire Oil Storage Terminal, located near the M1 motorway, Hemel Hempstead, in Hertfordshire, England. The terminal was the fifth largest oil-products storage depot in the United Kingdom, with a capacity of about 60 million Imperial gallons of fuel. The terminal is owned by Total UK Limited (60%) and Texaco (40%).
An oil terminal is an industrial facility for the storage of oil, petroleum and petrochemical products, and from which these products are transported to end users or other storage facilities. An oil terminal typically has a variety of above or below ground tankage; facilities for inter-tank transfer; pumping facilities; loading gantries for filling road tankers or barges; ship loading/unloading equipment at marine terminals; and pipeline connections.
Storage tanks are containers that hold liquids or compressed gases. The term can be used for reservoirs, and for manufactured containers. The usage of the word "tank" for reservoirs is uncommon in American English but is moderately common in British English. In other countries, the term tends to refer only to artificial containers. In the U.S., storage tanks operate under no pressure, distinguishing them from pressure vessels.
A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid migration in a human-made project, structure, or system. Geomembranes are made from relatively thin continuous polymeric sheets, but they can also be made from the impregnation of geotextiles with asphalt, elastomer or polymer sprays, or as multilayered bitumen geocomposites. Continuous polymer sheet geomembranes are, by far, the most common.
Secondary spill containment is the containment of hazardous liquids in order to prevent pollution of soil and water. Common techniques include the use of spill berms to contain oil-filled equipment, fuel tanks, truck washing decks, or any other places or items that may leak hazardous liquids.
A double-walled pipe is a secondary contained piping system. It is a pipe within a pipe, or encased in an outer covering, with an annulus between the two diameters. The inner pipe is the primary or carrier pipe and the outer pipe is called the secondary or containment pipe. The great majority of double-walled piping applications involve wastewater, groundwater, and process safety.
Fuel bladders, fuel storage bladders are a type of Flexi-bag used as a fuel container. They are collapsible, flexible storage bladders that provide transport and storage for bulk industrial liquids such as fuels.
A liquefied natural gas terminal is a facility for managing the import and/or export of liquefied natural gas (LNG). It comprises equipment for loading and unloading of LNG cargo to/from ocean-going tankers, for transfer across the site, liquefaction, re-gasification, processing, storage, pumping, compression, and metering of LNG. LNG as a liquid is the most efficient way to transport natural gas over long distances, usually by sea.
Grain LNG Terminal is a Liquefied Natural Gas (LNG) terminal on the Isle of Grain, 37 miles (60 km) east of London. It has facilities for the offloading and reloading of LNG from ships at two jetties on the River Medway; for storing and blending LNG; for truck loading; and regasifying and blending natural gas to meet UK specifications. The terminal can handle up to 15 million tonnes per annum of LNG, has storage capacity for one million cubic metres of LNG, and is able to regasify up to 645 GWh per day for delivery into the high pressure gas National Transmission System (NTS). The facility is owned and operated by National Grid Grain LNG Ltd, a wholly owned subsidiary of National Grid.
Tank leak detection is implemented to alert the operator to a suspected release from any part of a storage tank system, what enables to prevent from soil contamination and loss of product.
12 December 2005 [...] the bunds were unable to fully contain the escaped fuel and water used in fire-fighting [...] 14 December 2005 Damage to bunds caused by the intense heat of the fire caused significant loss of secondary containment [...]