ORIN successfully implemented a pilot study utilizing in-situ chemical oxidation to treat contaminated groundwater at an active truck terminal. Petroleum hydrocarbons were the remedial drivers. Due to the large amount of free phase diesel, ORIN recommended a remedial strategy combining mechanical and chemical oxidation remedies. ORIN’s approach saved the client approximately $45K over traditional remediation approaches.
- Site: Active Truck Terminal near Rockford, IL.
- Geology: 10 feet of silty clay overlying course to fine sand
- Groundwater velocity: average 10-4 cm/sec
- Contaminants: 9 mg/L BTEX
- 37 mg/L Naphthalene
- Average 2.5 feet Diesel
- Treatment chemistry:
- Catalyzed Sodium
- Persulfate (Na2S2O8)
- Treatment application: Chemical injection through a series of previously installed temporary drilled points.
Chemistries used during injection
Sodium Persulfate is a stable, highly soluble, crystalline material, which upon activation generates the sulfate radical, a very strong oxidant, capable of oxidizing a broad range of recalcitrant compounds. Laboratory studies in water have shown favorable destruction of Benzene, Toluene, Ethylbenzene and Xylene using catalyzed persulfate.
For example, the breakdown of BTEX compounds in the presence of catalyzed persulfate is as follows:
- Benzene: 15S2O8 + 12H2O + C6H6 → 30HSO4 + 6CO2
- Toluene: 18S2O8 + 14H2O + C6H5CH3 → 36HSO4 + 7CO2
- Ethylbenzene and Xylene: 21S2O8 + 16H2O + C6H4(CH3)2 → 42HSO4 + 8CO2
Summary of Implementation
The purpose of the pilot study was to provide information on the feasibility and logistics of full-scale treatment. To minimize the costs of multiple injections, ORIN recommended that temporary drilled injection points be installed. Prior to and during chemical injection a vacuum truck was utilized to remove the bulk of the LNAPL while ORIN utilized sodium per sulfate for the chemical destruction of the remaining higher contaminated areas. Seven injection points each received an average of 1,100 gallons of treatment chemistry. Evidence of oxidant influence was observed during the injection by the increase of key groundwater parameters such as DO and ORP in monitoring wells within the plume.
Post treatment sampling in May 2006. Awaiting approval of full-scale implementation.
The Bottom Line
Performing the pilot study demonstrated the effectiveness and feasibility for combining mechanical and chemical oxidation, reducing costs by $45K over traditional remediation approaches.