In 2012 in the rural midwest, a release of unleaded gasoline occurred at an Antea Group's oil and gas client’s main petroleum pipeline. Over 50,000 gallons of gasoline were estimated to have been released in a mixed agricultural/residential area, with more than 200 potable wells within a one-mile radius of the release.
The release occurred during a drought-stricken summer with temperatures often above 100°F. Groundwater levels were extremely low, and dry fractures and openings in the limestone allowed for rapid vertical movement of the gasoline to the regional water table about 90 feet below ground surface. Within days, gasoline compounds were found in vapor monitoring points and potable wells at several nearby residences.
The project objectives were clear for Antea Group’s client: remove as much gasoline as quickly as possible, prevent further off-site migration, ensure the safety of local residents, and provide alternate sources of water as needed. The desired outcome was to remove all of the gasoline that had been released and to negate the threat to human health and the environment.
- Removing and repairing the pipeline
- Removing impacted surface soil to shallow bedrock
- Drilling with sonic rigs to quickly map fractures
- Installing wells
Antea Group used its knowledge of the hydrogeologic system to position recovery wells and operate interim groundwater remediation and vapor recovery systems within two weeks of the gasoline release.
For the community, Antea Group activities included:
- Implementing a residential water well sampling program
- Overseeing the installation of point of entry carbon treatment units in 100 homes
- Delivery of bottled water to residences
To accomplish these tasks, hydrogeologists, remediation engineers, and environmental technicians versed in multi-media sampling were assembled into teams under the guidance and direction of the Antea Group project manager.
It was clear that recovering LNAPL, groundwater, and vapor would not restore the limestone aquifer to drinking water quality in a timely manner. Accordingly, water supply alternatives were evaluated. These alternatives included:
- Maintaining in-house treatment
- Drilling new wells for the affected residences
- Developing a local community water supply
- Extending the service area for the existing water supply system serving Antea Group’s client
Through Antea Group’s rapid response to the release, subsequent recovery operations and overall successful environmental management of the site have helped to minimize impacts to groundwater and the local community. In short order, the pipeline was repaired, over 7,200 tons of soil was excavated, five recovery wells, 28 monitor wells (including nested wells) and 75 bedrock vapor extraction wells were installed, a long-term multiphase Light Non-Aqueous Phase Liquid (LNAPL), groundwater and vapor remediation system was operational by June 2013, and 300 residential wells were being sampled on a regular basis.
It is estimated that the combined LNAPL, groundwater, and vapor recovery, along with soil excavation, have removed more than 20,000 gallons of petroleum. Of the 37 residential wells impacted by petroleum hydrocarbons, all have reported non-detectable results as of October and November 2014. Lastly, 122 connections to the expanded water supply system were completed and started providing potable water in November 2014.