Ex-Mobil Petrol Station

Underground storage tanks (USTs) and associated pipework at petrol stations are a potential source of hydrocarbons that may contaminate soil and groundwater.

This site, a petrol station since the early 1960s, was refurbished in 1989 by Mobil, and eventually decommissioned in 2008 with the removal of all USTs, pipework and pumps.

An environmental investigation commissioned by Mobil during the tank removal process confirmed that the majority of potential contamination issues had been addressed. Further investigation of the site was however necessary prior to development of the site, as part of due diligence pre-purchase investigations.

A review of previous environmental reports and Council information for the site confirmed that the location of the two large historic USTs had not been investigated. Also, further soil and groundwater sampling was necessary to determine heavy metal, total petroleum hydrocarbon (TPHs) and benzene, toluene, ethylbenzene and xylene (BTEX) concentrations, and to check for the presence of separate phase hydrocarbons.

Fraser Thomas Ltd undertook this additional investigation in order to obtain a Certificate of Compliance from Auckland Council and allow development of the site for other land uses.

Test pit and soil sampling results from across the site confirmed that while there was some evidence of hydrocarbons to the south and east of the concrete forecourt, this was minor and within current guideline levels for hydrocarbon contamination. Likewise, heavy metal concentrations met corresponding acceptance criteria. Groundwater sampling indicated that contamination of groundwater at the site was not occurring. These groundwater sampling results confirmed that the environmental effects of the hydrocarbons noted in excavations to the south and east of the forecourt were less than minor and had not impacted on groundwater.

These conclusions were verified by Council with the issue of a Certificate of Compliance for the site. A successful conclusion to an interesting project.

Services provided:

  • Environmental Engineering

Project cycle:

  • Preliminary and detailed site investigations
  • Certificate of compliance application