Modern Fibreglass USTs

- John Ewing, GHD

Historically petroleum USTs at service stations were steel tanks that were susceptible to corrosion, puncture and leakage. It is for this reason that many UPSS upgrade projects have been undertaken at service stations throughout Australia and the world. These steel tanks are typically replaced with fibreglass tanks, which are often double walled, with the internal cavity filled with a leak detection fluid which can be described as a non-toxic water based food dye and saline water solution.

When steel USTs are removed, they are typically de-gassed on site and transported for disposal or recycling at a licensed facility. New fibreglass tanks come with a 30-year internal corrosion warranty however the cost to transport these tanks back to the supplier and have them re-certified so they can be re-used with warranty in place, is greater than the cost of a new tank. For this reason, when fibreglass tanks are removed, they tend to be destroyed in-situ for disposal at landfill. During this process, the leak detection fluid is often lost into the ground. On the premise that this fluid comprises non-toxic constituents, no human health or environmental risk would result from in-ground destruction. However, as these modern fibreglass tanks are usually well within serviceable lives, the chemical properties of interstitial leak detection fluid has not been independently assessed in a remediation framework to GHD’s knowledge.

During remediation works carried out by GHD at a service station site, leak detection fluid from two large (90 kL) fibreglass USTs, installed in 2018, was sampled and analysed to inform disposal options. The results suggested there was more than just food dye and brine in the fluid. A range of volatile organic compounds were detected with high concentrations of acetone (6.5mg/L) and methyl ethyl ketone (MEK; 110 mg/L) as well as petroleum hydrocarbons. These compounds have toxic properties. They are known to depress the central nervous system and be harmful to the kidney. They are highly volatile and are an irritant to the nose and throat when breathed in, in high concentrations. Consultation with the supplier revealed that solvents are used during the construction of a fibreglass UST. It is hypothesized that when the internal cavity was filled with the leak detection solution, acetone and MEK leached from the fibreglass internal surfaces into the leak detection fluid causing these detections.

GHD and our subcontractor, Enviropacific Services (EPS), devised a method to safely remove the leak detection fluid and prevent it entering the environment without having to remove the intact tank with a crane and drain it from the bottom. The devised method allowed approximately 600 litres of toxic leak detection fluid to be removed and safely disposed of at a licensed facility and prevented a potential environmental pollution incident. In future, when decommissioning these types of USTs, consideration should be given to testing the leak detection fluid and removing it prior to UST destruction. In addition, detections of acetone, MEK or other VOCs in groundwater should be evaluated in relation to leak detection fluid as this may alter the conceptual site model for the site especially in cases where there was no other identified solvent source at the site yet solvents have been detected.

Article Published on 20/04/2023

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