Decommissioning of Storage Tanks After Commissioning in Chemical Industry
Dr. Pranjal Kumar Phukan D.Litt. (Hons)
Supply Chain expert
Dibrugarh, Assam

The term 'decommissioning' refers to the administrative and technical actions taken to allow the removal of some or all of the regulatory requirements from a facility.

Oil and chemical tank removals pose major environmental and health and safety risks. In 2016 a major utility company and their subcontractor were fined over £900,000 after a poorly planned tank removal job led to a serious pollution incident. In this incident 300 litres of residual sodium hypochlorite was diluted with water and discharged to the storm drainage system killing virtually all aquatic organisms for a 1 mile stretch of river . If this residual liquid had been pumped out, the incident could have been avoided preventing a major pollution incident and a substantial fine for the companies involved. There is a high risk of pollution during the installation, decommissioning and removal of underground storage tank (UST) systems. This pollution prevention guidance covers all USTs, including those containing petroleum, diesel, fuel oil, aviation fuel, waste oil, domestic heating oil and other potentially polluting materials such as organic solvents. Leaking underground tanks can be responsible for significant soil and groundwater contamination. Underground storage tanks typically contain oils, fuels, and chemicals and other types of liquids. Damaged, corroded, or poorly installed systems, and poorly maintained caps, seals and spill boxes can lead to leakage of these contaminants.

Decommissioning is increasingly becoming a major issue, since hundreds of facilities will end their operational lifetimes over the next decades. The decommissioning of oil and gas production facilities and their associated structures such as waste management and storage facilities gives rise to a variety of waste materials and items, some of which may be radioactive (e.g. sealed and unsealed sources, NORM scales, contaminated equipment, and concrete and soil). The decommissioning process involves numerous issues and activities including:
  • Development of the decommissioning strategy and plan and associated QA programmes
  • Development of disman tling and dec ontamination strategies;
  • Assessment of risks to workers, the public and the environment during and after the dec ommissioning activities;
  • Submissions to the regulator, e.g. plans, strategies, records, reports and survey results;
  • Approval by the regulatory body;
Tank Decommissioning Regulations
Given the potential risk to health and the environment, and the associated liability to property owners, removal of underground fuel storage tanks is highly regulated. The Technical Standards & Safety Authority (TSSA) regulates transportation, storage, handling and use of fuels to ensure conformance with the Technical Standards and Safety Act, 2000 (TSSA Act 2000 ). (Fig. 1)

Fig. 1: Tank decommissioning Fuel storage tank removals must be completed by a qualified Licensed Petroleum Contractor whose personnel are licensed in compliance with the TSSA Act, 2000 and who work in accordance with applicable Regulations, Codes and Standards.

Following removal of a fuel tank, an environmental assessment report must be completed in accordance with the requirements specified in the TSSA Fuels Safety Division Liquid Fuels Handling Code and “Environmental Protocols for Operating Fuel Handling Facilities in Ontario” and signed by a Qualified Person(e.g. Professional Engineer or Geoscientist). If contamination is discovered upon tank removal, remediation must be completed in accordance with O. Reg. 341 and O. Reg. 153.

(a) A typical tank decommissioning project will include:
  • Site visit & planning the pr oject
    We will conduct a site visit to assess the condition, specification and contents of the redundant tanks and ascertain if there are any site restrictions which would impact on the safe and timely removal of the tanks. Removing a tank can cause operational concerns for the site so it is essential a thorough assessment is undertaken to prevent any unnecessary delays. Before commencing any work the client will be issued with a thorough Risk Assessment & Method Statement to ensure they are satisfied that the project has been planned appropriately.
  • Sampling residual liquids
    In order to ensure health and safety is prioritized during the project and that the disposal method of any residual liquids is legally compliant and the most cost effective option a sample of the contents will usually be taken and sent to laboratory for analysis. In many cases residual liquids (usually oils) will hold commercial value which can be offset against the cost of the project. In some cases whole tank decommissioning projects can be completed on a cost neutral basis due to the commercial value of the oil. Unfortunately tanks are often left redundant for years before they are decommissioned which can allow the product to develop impurities which lower its commercial value.
  • Isolation and waste removal
    All residual liquids will be drained and/or pumped out and disposed of correctly. Any residues which cannot be drained will be removed mechanically by a vacuum tanker or where necessary manually by a confined space entry and breathing apparatus trained team. Confined Space Entry teams will be equipped with a gas detector to warn them of any dangerous e.g. explosive atmospheres. (Fig 2)

    Fig 2: Isolation of storage tank
  • Decontamination of tanks
    The tanks will be thoroughly cleaned to remove all hazardous residues, for steel tanks this will allow them to be recycled as scrap metal which will again have a commercial value to the client. Cleaning can be undertaken using water , a suitable degreaser or using steam. Cleaning can be undertaken in situ or at a licensed site after removal.
  • Purging
    If a tank is to be entered or hot works to be conducted the tank will require purging (the removal of flammable gases or vapors) or made inert before these works can commence .
  • Tank Cutting/Dismantling
    If access issues make it unsafe or uneconomical to remove the tank intact the tank can be dismantled in situ using hot and cold cutting techniques. Ideally the tank will be removed intact and dismantled at a more practical location. (Fig. 3)

    Fig. 3: Tank cutting process
  • Tank Removal & Disposal
    Once safe to do so the tanks will be removed via a crane/Hiab and transported under our upper tier hazardous waste license to a licensed waste facility for disposal. (Fig. 4)
    Fig. 4: Tank removal
  • Decontamination and removal of associa ted infrastructure
    This can include removal/capping of pipework and decontamination of plinths and bunds often to a level where they can be disposed of as inert waste.
  • Contaminated Land Testing & Remediation
    Where tanks have potentially caused contamination to the surrounding land we can undertake a Site Investigation to establish any contamination and can undertake remediation works to remove any contamination which is discovered.
Specific industries and different sizes and types of tank have specific guidance on how to decommission them. GPT structure every tank decommissioning project to follow the relevant legislation and best practice guidance that applies to the specific tank.

USTs are decommissioned on either a permanent or a temporary basis. Many tanks are temporarily decommissioned and then forgotten about. To avoid the risk of pollution, the Agencies recommend removal of tanks that are unlikely to be used again. The Blue Book contains comprehensive technical guidance on the decommissioning of USTs. Although it refers to the storage of fuels, the advice is often applicable to other products stored underground. Operators are particularly advised to refer to the Blue Book for information about the health and safety issues associated with decommissioning USTs. The Agencies are particularly concerned about the removal and disposal of the remaining product in the tanks and pipelines. All product and tank bottoms must be removed and disposed off correctly. Once this has been carried out, the risk of pollution is much less, as the pollution matter has been removed. The operator must also ensure that there is no residual contamination of the site such as petrol contamination of the soil and groundwater.