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~. Bioremed~at-on of a Pesncrde-Contammated Srte Yage ~ or .s <br />The more highly contaminated soils were pre-treated in slung bioreactors before piecemeal in the <br />solid-phase treatment area. A mobile soil slurry bioreactor system was used to treat more than 750 <br />cubic yazds of soil contaminated with up to 1,500 ppm 2,4-D and MCPA Three slung bioreactors <br />were set up at the site, along with equipment to slurry the soil and optimize the biodegradation <br />process. Material was withdrawn from a stockpile of highly contaminated soil and added to a trammel <br />unit that slurried the soil and separated out stones and rubble greater than 1/4 inch in diameter. The <br />slung was then pumped into 26,000-gallon bioreactors. Each reactor was capable of holding <br />approximately 60 cubic yards of soil Temperature, pH, and dissolved oxygen were controlled to <br />increase the rate of degradation. <br />Biodegradation of pesticides in the soil slung reduced 2,4-D and MCPA levels from 800 ppm (400 <br />ppm in the slurry) to less than 10 ppm in 13 days. The estimated half-life was 2.1 days. Upon <br />completion of the biological treatment, the slurry was spread onto the solid-phase treatment facility for <br />fiather COn aminant reduCti0n. <br />Solid-phase treatment of approximately 12,000 cubic yards of less contaminated soil (containing less <br />than 20O ppm of conraminanrc) was performed on the five-acre lined treatment bed. During the three <br />months of field operations, soil conditions were optimized for biological activity by daily tilling and <br />maintaining the soil moisture content between 8 and 15 percent by weight. The combined 2,4-D and <br />MCPA concentrations decreased from 86 ppm to 5 ppm during the three months of operation of the <br />solid-phase treatment facility. hz additioq more than one million gallons of contaminated water were <br />treated biologically. The water was treated in on-site bioreactors and then either dischazged or applied <br />to the solid-phase bioremediation facility to maintain moisture content. <br />Groundwater was treated with innovative in situ bioremediation techniques which reduced the <br />treatment time by half. An upgradient injection gallery was established to flush treated water and <br />nutrients, as required, through the con+aminant plume. During treatment, the groundwater was <br />monitored to guard against off-site migration. During the winter of 1987, more than five million <br />gallons of groundwater were treated. <br />The site has been restored to its original condition and a site closure plan prepared in accordance with <br />appropriate regulations. The rre~rmen+ took a total of three months. <br />The lead regulatory agency with jurisdiction over this project was the North Dakota State Department <br />of Health. <br />CONTAMINANT(S): pesticides, including 2,4-D, MCPA, triflural'm, alachlor, cazbofiuan <br />MEDIA: soil, groundwater, water <br />TECHNOLOGY: biological treatment, solid-phase bioremediation, slurry-phase bioremediation, m <br />situ bioremediation <br />REPORTED CONCENTRATIONS: 2,4-D, MCPA combined--10-200 ppm (86 ppm average) <br />http://www.epa.gov/bbsnnvrUattic/a2BT00025.html 1 i/15/98 <br />