By Sarah Sipak
In Canada, early commercial and residential heating systems used fuel oil or diesel fuel. Because of the size needed, it was common to use underground storage tanks (USTs) for fuel storage. The presence of a UST is usually indicated by fill ports that are generally flush with the ground surface and vent pipes that are located above grade. USTs can vary in size and are commonly used for the storage of fuel oil, gasoline, diesel and solvents.
Storage tanks that are placed in the basement of a structure are not considered to be a UST. Those that are placed inside a building or along the exterior of a structure are considered to be aboveground storage tanks (ASTs). ASTs can also vary in size and are commonly used for the storage of waste oil, gasoline, diesel and fuel oil.
Why are storage tanks an issue?
Older tanks, constructed prior to the mid-1980s, were made of thin, uncoated mild steel, which is highly likely to corrode over time. These older tanks were usually placed directly into the ground without secondary containment, and as they corrode, their contents can leak into the surrounding soil and/or groundwater.
ASTs that are placed along the exterior of a building, where the surroundings are not maintained properly, can experience an increase of moisture build-up along their bellies because of the overgrown vegetation, which leads to corrosion and leaks.
The presence or potential presence of USTs and ASTs are common sources of soil contamination in Ontario. If contamination is expected or detected, the tank should be removed prior to causing further subsurface contamination. Following removal of the tank, an environmental subsurface investigation should be conducted in order to verify and/or refute the presence of contaminant concentrations in the soil and/or groundwater in the vicinity.
Who regulates storage tanks?
In Ontario, the Technical Standards and Safety Authority (TSSA) regulates underground storage tanks that are used to store petroleum products. The TSSA registers qualified contractors and inspectors that work with fuel tanks and systems, and they are required by law to be trained and certified as petroleum mechanics. Only these certified contractors should conduct repairs, inspections and tank removals, to ensure that the tank is properly examined, and the issue is dealt with in accordance with regulations and protocols.
How to properly remove an underground storage tank
In order to remove a UST, a qualified and experienced environmental contractor is retained to conduct the tank removal. An environmental consultant is also retained to oversee the tank removal completed by the contractor and to conduct a verification sampling program after it is done.
The removal process begins with purging the remaining tank contents and any vapours. Once the tank is deemed “clean”, surface coverings and soil in the vicinity of the tank are removed. When the tank and piping are exposed, the piping is disconnected and removed, followed by removal, shearing and off-site disposal of the tank.
Subsequently, verification soil sampling of the walls and floor of the former tank nest is conducted to confirm that no soil impacts are present. If there is evidence of potential impact to groundwater, then monitoring wells should be installed, followed by the collection of samples for laboratory analysis. Once laboratory results indicate that the remaining material in the vicinity of the former tank meets applicable site condition standards, the excavated area is backfilled, graded and restored.
Upon completion of the UST removal and a successful soil and/or groundwater sampling program, a report is developed and provided to the TSSA for regulatory review and compliance.
Minimizing risk to environment while having a tank on site
Early detection of a leak and/or spill associated with a storage tank, identifying the source of the release, and assessing the soil and/or groundwater conditions in the vicinity of the tank are three important factors. Leaking tanks can have impacts on property value and drinking water wells. The build-up of vapours in underground structures in close proximity to a tank can be harmful to human health and safety.
In order to minimize risk to the environment, a tank and associated piping must be inspected and maintained regularly. Generally, a tank tightness test is conducted to verify and/or refute if a leak is occurring. Proper management of liquid levels can reveal a significant loss of liquid in a short period of time.
If a leak is suspected or confirmed, the source of the release should be minimized immediately. Commence the tank repair or removal process, and have the surrounding soil sampled and analyzed for any contaminants of potential concern associated with the released liquid.
Sarah Sipak is with Rubidium Environmental. This article appears in ES&E Magazine’s June 2019 issue.