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V V REMOVAL AND DISPOSAL OF USED UNDERGROUND PETROLEUM STORAGE TANKS 7 V from volatile vapors. Air pressure in-the tank must not 4.3.2 The tank vapor space is to be tested by placing v exceed 5 pounds per square inch gauge. the combustible gas indicator probe into the fill opening 4.2.6 One of the safest and simplest methods for with the drop tube removed. Readings should be taken vapor-freeing a tank is to fill the tank with water. at the bottom, middle, and upper portions of the tank, However, in certain areas, regulatory requirements for and the instrument should be cleared after each reading. treatment/disposal of water used in the vapor-freeing If the tank is equipped with a non-removable fill tube, process may make this method cost-prohibitive. Before readings should be taken through another opening. employing the method described in 4.2.6.1 through Liquid product must not enter the probe. Readings of 4.2.6.3, consult local regulations. 20 percent or less of the lower flammable limit must be obtained before the tank is considered safe for removal 4.2.6.1 Fill the tank with water until the floating from the ground. �— product nears the fill opening. Remove the floating 4.3.3 Combustible product and place it in a suitable container for proper gas indicator readings may b disposal.Care should be exercised to ensure that neither misleading where the tank atmosphere contains less nor water is spilled into the tank excavation. than 5 percent by volume oxygen, in a tank vapor- product . freed with CO2; N2, or another inert gas. In general, 4.2.6.2 In the process of filling the tank with water, readings in oxygen-deficient atmospheres will be on the flammable vapors will be expelled through both the vent high, or safe,side. It may be desirable to use an oxygen and fill openings,but primarily at the fill opening.Nor- indicator to assess the oxygen concentration. mal safety precautions should be observed.To minimize this escape of vapor through the fill opening, the open- 4.4 Removal ing may be temporarily capped. 4.4.1 After the tank has been freed of vapors and 4.2.6.3 When the tank is free of vapor, pump out the before it is removed from the excavation,plug or cap all water and dispose of it in accordance with local regula- accessible holes. One plug should have a 1/8-inch vent tions. hole to prevent the tank from being subjected to ex- cessive differential pressure caused by temperature 4.2.7 Steam can be used to clean and vapor-free a changes.The tank should always be positioned with this itank.However,a large static charge can build up on the vent plug on top of the tank during subsequent trans- nozzle of the steam jet. Insulated objects on which the port and storage. steam impinges can also become charged. If steam is to be used for either purging or cleaning a tank or other 4.4.2 Excavate around the tank to uncover it for equipment, the steam discharge nozzle and all conduc- removal. Remove the tank from, the excavation and tive insulated objects subject to impingement or conden- place it on a level surface. Use wood blocks to prevent sation should be bonded to the tank or be grounded. movement of the tank after removal and prior to Steam purging of tanks should be avoided when suitable loading on a truck for transportation. Use screwed L alternatives are available. Further reference to steam (boiler) lu s P 8 to plug an Y corrosion holes in the tank cleaning of tanks is found in NFPA 327. shell. ,r 4.4.3 When partially or totally removing an existing underground storage system, a small amount of con- 4.3 Testing taminated backfill maybe encountered.The contamina- ,r 4.3.1 The tank atmosphere and the excavation area tion can be due to minor spills and drips during previous should be regularly tested for flammable or combustible operation of the facility or from drips and minor spills that may occur during removal. Contaminated backfill vapor concentrations until the tank is removed from may be a potential safety and environmental hazard. both the excavation and the site. Such tests are to be made with a combustible gas indicator which is properly Spills or drips should.be contained to minimize con- calibrated according to the manufacturer's instructions tamination during removal. If contamination is severe, (typically on pentane or hexane in air), and which is consult local environmental officials, the fire marshal, thoroughly checked and maintained in accordance with or the USEPA for assistance and requirements.See API the manufacturer's instructions.Persons responsible for Bulletin 1628 for further information. • testing must be completely familiar with the use of the 4.4.4 Tanks should be labeled after removal from the .. instrument and the interpretation of the instrument's ground but prior to removal from the site.Regardless of readings. the condition of the tank, the label should contain a