A major integrated oil company retained the services of Antea®Group to manage environmental liability at a bulk storage and distribution facility that supplies gasoline, diesel fuel, and other refined petroleum products to Minnesota, Iowa, and Wisconsin.
The property presented a series of unique challenges including multiple LNAPL plumes, LNAPL identified within karst bedrock, bedrock fractures impacted with LNAPL with identified impacts over 180-ft below grade, and impacts to private drinking water supplies.
Site assessment activities included hollow-stem auger drilling, air-rotary drilling, downhole video logging, packer tests, and installation of multi-level sampling wells to provide vertical dissolved phase delineation.
In addition, tracer studies and private well sampling assessments to assess the direction and extent of the dissolved phase plume.
Remediation system design, installation, operation and maintenance activities included multi-phase and dual-phase extraction. Dual-phase design was based on pilot tests using packers to isolate vertical zones within the fractured bedrock so that the extraction targeted only those zones that had substantial hydrocarbon impacts.
In the former loading rack area of the facility, 7,558 tons of hydrocarbon-impacted soil was excavated and disposed of. The excavation was backfilled with clean granular fill mixed with 50 tons of agricultural grade gypsum for the purpose of adding sulfate to the ground water to facilitate anaerobic biodegradation of dissolved petroleum impact.
The system achieved its regulatory ordered clean up criteria and active remediation at the site was completed within seven years of system start up. During its operation, the client was recognized for exemplary compliance with state regulations and their commitment to protect and preserve the environment. The state regulatory agency awarded a prestigious Certificate of Commendation for the environmental management of the facility.
Antea Group provides ongoing services at the site including geographical information and technical data management systems, ground water flow modeling and well sample monitoring.