Antea Group was tasked with investigating a railroad yard that had been the site of train diesel fuel contamination, which had been occurring over a period of years. As a result, the diesel fuel had impacted a large volume of soil, and free product was present both on-site and downgradient of the railroad property, covering an area of several acres.
Antea Group installed a product recovery system utilizing five groundwater extraction wells equipped with free product skimmer pumps. The disposal of the produced water to the sanitary sewer would have normally cost the client over $250,000 per year in sanitary sewer discharge fees. However, Antea Group received permission from the DNR to infiltrate 90 percent of the 350 gpm flow rate as part of an in situ aqueous bioremediation system.
Consequently, approximately 300 gpm of water was oxygenated to dissolved oxygen concentrations of 20 to 40 mg/L using on-site oxygen generators. Along with oxygen, inorganic nutrient amendments, including nitrogen and phosphorus, were added prior to infiltration. The in situ bioremediation system saved Antea Group’s client $740,000 in sewer discharge fees over the three year operation period, delivering enough dissolved oxygen mass to biodegrade over 20,000 pounds of hydrocarbon contaminants. On-site soil and groundwater treatment also involved air sparging and bioventing by air injection in areas where infiltration of oxygenated water was not feasible.
After three years of treatment, free product was no longer observed, and most monitoring wells contained dissolved contaminant levels below DNR enforcement standards. Antea Group received permission from the DNR to shut down treatment systems, and is currently collecting data for a natural attenuation site closure in order to address any remaining residual hydrocarbon contamination.
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