ORIN successfully implemented a pilot study utilizing in-situ anaerobic bioremediation to treat contaminated soil and groundwater. Chlorinated hydrocarbons were the remedial drivers. Due to resounding success of the pilot test, the client and regulatory agency deemed no further action was necessary.

Site Characteristics

  • Site: Former Manufacturing Facility in Des Moines, IA.
  • Geology: 25 feet of silty, lean clay overlying fat clay.
  • Groundwater velocity: average 1.6×10-4 cm/sec
  • Contaminants: TCE – 11,500
  • micrograms per liter (ug/L)

Remediation Approach:

  • Treatment chemistry: EOS®
  • Treatment application:
  • Chemical injections utilizing
  • direct push technology (DPT)

Chemistry Used During Injection

The EOS® process provides an innovative, low-cost approach for distributing and immobilizing biodegradable organic substrates in contaminated aquifers to promote in-situ anaerobic biodegradation of chlorinated solvents. EOS® consists of food grade soybean oil, surfactants, macro and micronutrients, and vitamins blended to form a stable micro-emulsion with small, uniformly sized droplets. Once injected, the oil droplets stick to the sediment surfaces providing a residual oil phase. The EOS® then serves as a carbon source for cell growth and an electron donor for energy generation, supporting long-term anaerobic biodegradation of the target contaminants.

This approach provides good contact between the slowly biodegradable organic substrate (oil) and the contaminants and substantially reduces initial capital and long-term operation and maintenance costs. For example, common organic solvents utilizing EOS® is completely reduced to ethene according to the following equations:

  • PCE: C2Cl4 + 4H2 → C2H4 + 4H+ + 4Cl-
  • TCE: C2HCl3 + 3H2 → C2H4 + 3H+ + 3Cl-
  • DCE: C2H2Cl2 + 2H2 → C2H4 + 2H+ + 2Cl-
  • VC: C2H3Cl + H2 → C2H4 + H+ + Cl-

Summary of Implementation

The purpose of the pilot study was to provide information on the feasibility and logistics of full-scale treatment as well as the ability to address the off-site migration of the contaminants. Twenty-six injection points were advanced using DPT throughout the area. A barrier wall injection was also implemented to intercept the advancing plume before migrating off-site. The vertical injection zone extended from an average depth of 44-feet below ground surface (ft. bgs) up to 16-ft. bgs. Each injection point received approximately 300 gallons of 15% concentration EOS® treatment chemistry. A total of 7,870 gallons of EOS was injected over a two-day period.

Effectiveness

Six months following the pilot test, PCE concentrations in the source area decreased from 11,500 ug/L to below 100 ug/L. The client and regulatory agency deemed no further action was necessary.

The Bottom Line

The pilot study demonstrated the effectiveness and feasibility for utilizing EOS® to treat contaminated soil and groundwater. The barrier wall intercepted the advancing plume – degrading the contaminants before migrating off-site – thereby eliminating the need for full-scale treatment.