Project Description

CASE STUDY: Chemically Oxygenated Granular Activated Carbon {COGAC™) Injection

This case study presents site information, remedial injection remedial material, injection method and post injection results at a petroleum hydrocarbon underground storage tank release site.

Site Information

  • Former Leaking Underground Storage Tank Project (Colorado)
  • Chemicals of concern (COCs) BTEX, MTBE, and TVPH
  • Predominant lithology in the unsaturated zone is Silty Clay
  • Predominant lithology in the saturated zone is Claystone
  • Depth to groundwater ranges 5 to 21 feet
  • Hydraulic Conductivity is 1.55-6 cm/sec
  • Hydraulic gradient is 0.138 ft./ft.

Contaminant Mass Calculation

A contaminant mass calculation was prepared to determine the required remedial mixture and solution quantities for the treatment area. Remington utilized average soil and groundwater concentrations and a 1,800 square feet treatment area to calculate contaminant mass. Based on these assumptions, the calculated mass was estimated to be 107.6 pounds. Table 6 summarizes the contaminant mass calculation and COGAC™ quantity summary for the treatment area.

It was also estimated that injection efficiency in this type of material was 20% and that 5 pounds of remedial material was needed for each pound of contaminant. Therefore, the estimated dose, based on the contaminant mass calculation for the site was approximately 2,691 pounds. It should be noted that, the last assumption is just that, and is currently being evaluated using ongoing field studies.

Injection Design Summary

  • 1,800 square foot treatment area
  • Average BTEX, MTBE and TVPH 5,800 ppb
  • Site specific target levels to obtain site no further action
  • Varied treatment intervals 8 to 23 feet
  • 23 injection points
  • 15.5% COGAC™ Solution
  • Direct push technology for injection points
  • Average 90 gallons per injection point
  • 2,673 pounds of COGAC™ remedial material
  • Injections completed in 2 days.

COGAC™ Remedial Injection Results

As shown on the following graphs, dissolved benzene concentrations decreased after the COGAC™ injection event. To obtain site closure, site specific target levels were utilized for MW-2 and the state dissolved benzene MCL of 5 ug/L was required for MW-9 and MW-13. Based on these results, the COGAC™ injection was successful in remediating the calculated remedial mass remaining at the site, therefore achieving regulatory remedial goals for no further action for this project.