ORIN successfully implemented in-situ chemical oxidation using catalyzed persulfate to treat contaminated groundwater at an active gas station in Powder Springs, GA. Gasoline and BTEX compounds were the remedial drivers. The site achieved closure status approximately two months after injection.

Site Characteristics:

  • Site: Active Gas Station in Powder Springs, GA Geology: Silty clay with fine- to medium-sand lenses Hydraulic Conductivity: average 10-4 cm/sec
  • Contaminants:
    • Benzene: 2,900 ug/L
    • Toluene: 1,300 ug/L
    • Ethylbenzene: 2,400 ug/L
    • Xylenes: 8,100 ug/L

Remediation Approach:

  • Treatment chemistry: Sodium Persulfate catalyzed with calcium peroxide-based product
  • Treatment application: In-situ injection

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 complete 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

Using Geoprobe direct push technology, 1 .-inch (in.) diameter steel rods with disposable tips were advanced to a target depth of 25-feet below ground surface (ft. bgs) in order to facilitate chemical injection. Approximately 150 gallons of catalyzed sodium persulfate at 20- to 25-percent solution was injected into each of the forty injection points at four depth-specific intervals. Each interval received approximately 35- to 40-gallons of treatment chemistry. The injection points were spaced in a triangular grid pattern to treat the bulk of the contaminant plume and a barrier wall pattern to prevent further offsite contaminant migration. Exact injection point location and volume of injected solution varied depending on unforeseen site conditions and soil matrix properties.

Effectiveness

The catalyzed sodium persulfate treatment chemistry reduced the BTEX contaminant concentrations to below site closure levels in approximately one month. The residual calcium peroxide in the subsurface will continue to provide an oxygen source and promote bioremediation.