ORIN successfully treated unsaturated soils contaminated with creosote compounds including pentachlorophenol (PCP) and diesel range organics (DRO) using ex-situ chemical oxidation at a former wood frame manufacturing facility located in Lester Prairie, Minnesota. Two different treatment chemistries were implemented due to differing soil chemistries at the site. ORIN’s approach saved the client approximately $500,000 over traditional remediation approaches.
- Site: Former Wood Frame Manufacturing Facility
- Geology: Silty Sand; 3-foot thick organic-rich silt
- Depth of treatment (GW level): 5-ft. below surface
- Max Contaminant Concentrations and Treatment Goals (ppm):
Area One Area Two Goals DRO 3,530 17,100 N/A PCP 192 1,620 120
- Treatment chemistries: Fenton’s Reagent (hydrogen peroxide and ferrous sulfate acidified with sulfuric acid) and Alkalineactivated Sodium Persulfate
- Treatment application: Ex-situ remediation using an excavator to mix contaminated soil and treatment chemistry.
Chemistries used during ex-situ remediation
The Fenton’s Reagent treatment chemistry included addition of acid to reduce the pH to < 5. The preferred Fenton’s Reaction is:
- H2O2 + Fe+2 ➜ OH. + OH- + Fe+3
Sodium Persulfate is a stable, highly soluble, crystalline material, which upon activation generates the sulfate radical. One way to activate persulfate is add an alkaline substance such as lime.
- S2O8-2 + CaOH→ HSO4- + SO4-2 + óO2 + Ca
Summary of Ex-situ Implementation
Ex-situ remediation at this site involved the application of the treatment chemistries directly onto the exposed soils. An excavator was present to displace a volume of soil down to depth. A portion of that soil was placed back into the excavated hole while treatment chemistry was applied to the soil. The excavator continually mixed the soil and chemicals together until the desired amount of treatment chemistry was applied. More soil was added from the displaced volume while additional chemical was applied and mixed thoroughly. This process was repeated until the desired consistency and chemical volume was applied to the entire targeted soil volume.
Soil sampling performed during treatment showed successful remediation of PCP in Area One using Fenton’s Reagent. However, most likely due to high DRO concentrations, Fenton’s Reagent was ineffective at Area Two after multiple treatments. Alkaline-activated Persulfate successfully reduced PCP levels in Area Two using one treatment. The lime used for alkaline activation served a dual purpose: it catalyzed the creation of the sulfate radical while simultaneously extracting PCP from the creosote.
One week following treatment, soil samples were taken at various locations within the treatment areas. Fenton’s Reagent and alkaline-activated persulfate treatment chemistries reduced PCP concentrations to below treatment standards for nonhazardous waste disposal.
The Bottom Line
ORIN successfully reduced contaminant levels in both areas by using the proper treatment chemistry. The treated soils were disposed of as non-hazardous waste at a nearby Minnesota Subtitle D Landfill. Full scale remedial costs were ultimately reduced by approximately $500,000 compared with traditional dig-and-haul remediation approaches.