Technology:
Land Treatment
- Land treatment unit (LTU) constructed with outer dimensions of 300 x 495 ft
- LTU constructed in layers, over HDPE, silty sand, gravel, and clean, silty sand base
- 1,100 to 1,500 yds3 spread over LTU each year, to a depth of 6-8 inches
- Operation included weekly cultivation, irrigation, lime addition, and cow manure application
- Treatment conducted from May through October each year from 1986-1994 (9 "treatment seasons")
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Contaminants:
Polynuclear Aromatic Hydrocarbons (PAHs), Other Semivolatiles Nonhalogenated
- Total PAH concentrations ranged from 33,982 to 70,633 mg/kg
- Individual PAH concentrations ranged up 21,319 mg/kg
- Benzene extractable concentrations ranged from 66,100 to 112,500 mg/kg |
Results:
- Cleanup goal of 8,632 mg/kg for total PAHs was met for all nine treatment seasons
- At completion of treatment, total PAH concentration ranged from 608-795 mg/kg throughout the LTU
- Cleanup goal of 21,000 mg/kg for MCE hydrocarbons was not met for any treatment season
- At completion of treatment, MCE hydrocarbon concentration ranged from 24,800-26,900 mg/kg throughout the LTU
- A cover was placed over the LTU after completion of treatment |
Description:
The Burlington Northern site was the location of a railroad tie treating plant that operated from 1907 to 1985. Wood preserving processes operated at the site involved pressure treatment using a heated creosote/coal tar or creosote/fuel oil mixture. Wastewater generated from the wood preserving processes was discharged to two shallow, unlined surface impoundments for disposal. In the 1980s, EPA determined that soil beneath these two surface impoundments, as well as soil in three other areas at the site (the process, drip track, and black dock areas) were contaminated. Total PAH concentrations for visibly-contaminated soils in the surface impoundments were measured as high as 70,633 mg/kg, with individual PAHs measured as high as 21,319 mg/kg. Concentrations of benzene-extractable constituents in the surface impoundment soils ranged from 66,100 to 112,500 mg/kg.
Based on a consent agreement, EPA issued an Enforcement Decision Document (a predecessor to a ROD) in June 1986, which required Burlington Northern to treat visibly-contaminated soils and sludges using on-site land treatment. The land treatment unit (LTU) used in this application had outer dimensions of approximately 300 by 495 feet (150,000 ft2) and an area available for treatment of approximately 255 by 450 feet (115,000 ft2). Each year from 1986 through 1994 (nine years total), between 1,100 and 1,500 cubic yards of contaminated soil and sludge were spread over the LTU to a depth of 6-8 inches. Land treatment was conducted from May through October (the "treatment season"), and included weekly cultivation, irrigation, lime addition, and cow manure application. The analytical data from the LTU at the completion of treatment indicate that the cleanup goal was met for total PAHs with the concentration of total PAHs ranging from 608 to 795 mg/kg throughout the depth of the treated soil and sludge. However, MCE hydrocarbons in the treated soil ranged from 24,800 to 26,900 mg/kg, and the cleanup goal was not met. Therefore, a cover was placed over the LTU.
MCE hydrocarbons were not treated to below the cleanup level because a "plateau effect" limited the extent of biodegradation of these constituents. However, MCE hydrocarbons are no longer typically used as a performance measure for land treatment systems. This application demonstrated that treatment efficiency for PAHs decreased with increasing number of ring structures in the PAH molecule (e.g., two-ring more efficient, four-ring less efficient). The land treatment application at Burlington Northern was PRP-lead, and no information on actual total costs or unit costs incurred is provided in the available references. |
