Swift action to investigate and remedy a leak, minimised the impact on the environment, cost to the provider and risk to nearby receptors.
Environmental Services, Contaminated Land
Our Environmental Services team identified the presence of unanticipated light non-aqueous phase liquid (LNAPL) in the monitoring wells at a confidential oil industry site during a routine site visit. Quick action was taken by the team to identify the leak and assess the extent of the impact.
The LNAPL was analysed by a laboratory and found to be consistent with fresh petrol. A leak was identified beneath a dispenser and was subsequently repaired. The team supervised the excavation of test pits across the site to visually assess the soil at groundwater level in multiple locations. Standpipes were installed within the test pits to assist with abstraction of the LNAPL. Additional monitoring wells were also installed to further delineate the LNAPL and dissolved phase hydrocarbon contamination.
A Class 3A vacuum truck was used between September 2021 and May 2022 to remove LNAPL from monitoring wells at the site, managed by the team. This work was completed under emergency provisions with cooperation from local regulatory agencies. The LNAPL removal involved lowering a brass pipe connected to the vacuum truck to just above the level of the LNAPL in the monitoring wells. The vacuum from the truck was used to remove vapour, LNAPL, and water. Wells nearest to the tank pit were targeted first to draw the LNAPL back towards the centre of the site and prevent offsite migration. A total of 19,000L of LNAPL/water mix was removed from the monitoring wells at the site.
4Sight completed regular groundwater monitoring which showed successful remediation of LNAPL contamination in the groundwater. A set of two nested wells were installed at the site to assess the thickness of the dissolved phase hydrocarbon contamination. Each of the nested wells had two discrete screens allowing for four separate groundwater monitoring depths. Groundwater samples were carefully collected from each screen depth using micro-purging techniques. Results showed that dissolved phase contamination was limited to the top 6 m of the shallow groundwater aquifer. Monitoring results showed that the site no longer posed a risk to receptors and that conditions in the groundwater were suitable for natural attenuation.
The level of expertise of the Environmental Services team enabled the investigation and remediation to be mobilised quickly, minimising the impact on the environment and risk to nearby receptors.