During a 1989 derailment in East Central North Dakota, two ruptured tank cars released anhydrous ammonia into the soil.

Although the initial cleanup included an extensive excavation, site access problems precluded complete removal of the impacted soil. Braun Intertec was retained in 1996 to assist in enhancing the remedial efforts onsite with the goal of expediting regulatory closure.

Challenges

The elevated levels of nitrogen measured in the local groundwater suggested that nitrogen-impacted soils and groundwater remained on site. Groundwater recovery and treatment efforts had not effectively reduced contaminant concentrations, prompting the local regulatory body to require indefinite long-term remediation.

Solutions

We proposed an innovative strategy using plant-based remediation (phytoremediation) to remove nitrate from the local groundwater and reduce the total mass of nitrogen in the soil at the site. The unique approach was implemented as follows.

Our project team includes personnel from the U. S. Department of Agriculture, Agriculture Research Service (ARS). The ARS has developed a unique genetically altered strain of alfalfa (known as Ineffective AGATE) that cannot fix nitrogen from air. We worked with the ARS to use this site for the first application of Ineffective AGATE in a non-laboratory situation.

A field was planted with the alfalfa during June of 1996. An enhanced remediation system was developed that incorporated phytoremediation. The derailment site and an adjacent field were planted with alfalfa, a deeply rooted perennial crop with a large nitrogen uptake potential.

The alfalfa was irrigated with nitrogen-impacted groundwater withdrawn from the existing recovery wells. Nitrate extraction therefore occurred from both impacted soil and groundwater. The efficiency of this environmentally friendly operation was enhanced by the first field application of the ineffective AGATE alfalfa.

In three years, this cost-effective treatment system remediated more than one million gallons of impacted groundwater and reduced nitrogen concentrations in both soil and groundwater across the site. Following a relatively short period of post-remedial monitoring, final closure was granted by the State of North Dakota.

Our unique approach to this remediation project yielded many benefits for the client. First and foremost, the local regulatory body signed off on the work plan and granted closure of the site within a three-year timeframe. Secondly, due to the potential for the AGATE alfalfa variety to be used as a phytoremediation agent, the ARS designated funds and personnel for use on this project, resulting in reduced costs for the client. Finally, the client benefited by receiving public acknowledgement and positive recognition from the media.