Poly-Aromatic Hydrocarbons
 
Coal Tar Contaminated Soil Treatment
 

ETEC developed a specialized multi-enzyme complex for the biological degradation of polynuclear aromatic hydrocarbons (PAHs) in coal tar. Using a co-oxidation process in field application, ETEC achieved greater than 80% degradation of carcinogenic PAHs in soil and more than a 90% reduction compared against risk-based cleanup levels.
 
Risk Based Corrective Action and Bioremediation:  A Perfect Match
 
In the past, numerical cleanup standards have been applied to most sites without regard to site specific risk factors. With the advent of risk based corrective action (RBCA), much more reasonable and achievable cleanup levels may be obtained from the regulators. At this site, the Utah State Department of Environmental Quality set a RBCA cleanup standard for the site of 79 ppm for the seven suspected carcinogens in the PAH family:
   
  • Benzo(a)anthracene
  • Chrysene
  • Benzo(b)flouranthene
  • Benzo(k)flouranthene
  • Benzo(a)pyrene
  • Dibenzo(a,h)anthracene
  • Indeno(1,2,3-cd)pyrene
 
 
The treatment was carried out in a standard soil landfarm over a period of 132 days. Initial soil sampling showed a total PAH concentration of 1,453 ppm, of which 432 ppm constituted the seven carcinogenic compounds. Applying RBCA multipliers to the carcinogenic constituents resulted in risk-based concentration of 170 ppm.

After only 50 days of treatment in the landfarm, the total PAH concentration was reduced an astounding 77% to 334 ppm, while the carcinogenic PAHs of concern were similarly reduced by 71% to only 127 ppm. More importantly, applying RBCA multipliers to the compounds resulted in a mere 30 ppm. The RBCA cleanup level was achieved in less than 2 months of treatment time!
 
   
At the request of our client, the treatment process was continued in an attempt to achieve further reductions in the contaminant concentrations to provide a greater comfort level regarding future clean up requirements. Soil testing after 73 days showed little additional contaminant reduction, but final testing after 132 days of treatment showed total PAH degradation to a low 242 ppm, an 83% reduction from the initial levels. The seven carcinogenic PAH concentrations also further reduced to 81 ppm, an 81% reduction from initial levels. RBCA calculations resulted in a decrease to a low 17 ppm, a full 90% reduction from their original levels, nearly five times less than the regulatory RBCA cleanup level.
 
Summary of Individual Compound Degradation