Rural Response & Remediation: Cottonwood, Minnesota
Leggette, Brashears & Graham, Inc. (LBG) responded to an 8-inch diameter main line release of gasoline and fuel oil in a remote agricultural setting. An estimated 725 barrels of released petroleum impacted over 5 acres of property. A field drain tile in the vicinity of the release emptied into a drainage ditch that discharged to a local river. Initial response actions included excavation of grossly impacted soil, removal of sections of field drain tile, and installation of absorbent booms in the drainage ditch. LBG conducted an emergency response investigation (including test pits, Geoprobe soil sampling, and monitor well installations) to quickly delineate impacts to soil and groundwater, and performed groundwater and surface water receptor surveys. LBG also coordinated and supervised landfarming of petroleum-impacted soil.
LBG analyzed alternative response actions for soil and groundwater remediation, prepared detailed cost estimates for each alternative, and recommended a simple and cost-effective approach. Approved alternatives included phytoremediation using hybrid poplar trees, an in-situ biopile design utilizing crops as mulch to minimize material and transport costs, and ex-situ thermal treatment and re-burial.
LBG designed, installed, operated, and maintained a flexible multi-phase extraction and groundwater treatment system in a very short time frame. Over 5,000 gallons of free product and 11,000 pounds petroleum hydrocarbons were removed in less than 2½ months of operation. System flexibility allowed for low cost subsequent system enhancements with soil vapor extraction (SVE), groundwater recovery, and SVE Air/ Liquid Contactor (SALCO) technologies to further improve hydrocarbon recovery efforts. Cost saving measures implemented included: landfarming of excavated and impacted soil; spray-irrigation of treated groundwater; surface installation of pipes for seasonal operations of liquid recovery systems; use and integration of client-owned equipment; use of local contractors for system operation and maintenance; recycling of recovered petroleum; and focused analyses of monitored natural attenuation (MNA) parameters to support site closure requests. In three summers of aggressive operations, the systems removed all recoverable free product from the subsurface and the site was administratively closed by the regulatory authority.