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 in Colorado.
In the treatment area, soil lithology consists of sandy clay from approximately 10 to 20 feet below ground surface (bgs) overlain by clay. Depth to groundwater ranges from 12.1 to 14.7 feet bgs. Based on a soil
sample collected in the treatment area, soil impacts were documented at approximately 10 feet bgs. Groundwater impacts at monitoring wells MW-1 and MW-2 were present above state regulatory standards, therefore requiring active remediation.
COGAC™ is a patented remedial material developed by Remington Technologies. COGAC™, mixed in a slurry, consists of Activated Carbon, Sodium Persulfate and Calcium Peroxide. COGAC™ remedial material combines the adsorptive capacity of activated carbon with the strong oxidation of sodium persulfate activated with calcium peroxide. The calcium peroxide converts to hydrogen peroxide over time in the subsurface providing extended oxidation followed by bio-stimulation of petroleum hydrocarbon degrading aerobic bacteria present as a result of the current and past subsurface conditions.
Contaminant Mass Calculation and Quantities
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 1,700 square feet treatment area to calculate contaminant mass. Based on these assumptions, the calculated mass was estimated to be 88.5 pounds. To account for the amount of time that has elapsed since the 2007 soil analytical data was collected in the treatment, unknown effectiveness of 2012 mobile soil vapor extraction/air sparging bi-monthly events and ongoing natural attenuation, an estimated 35% reduction in the contaminant mass was applied to the calculation resulting in a total of approximately 47.8 pounds. The contaminant mass calculation and COGAC™ quantity summary for the treatment area is attached for reference.
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 1,195 pounds. It should be noted that, the last assumption is just that, and is currently being evaluated using ongoing field studies.
Remedial Injection Method
The remedial injection method used at the COGAC™ injection site utilized Direct Push Technology (DPT). Twelve temporary injection points were advanced on July 23, 2013. 100 gallons of 12% COGAC slurry was injected at an injection interval of 12 to 15 feet bgs. A total of 1,200 gallons were injected on a 10-foot spaced grid layout within the treatment area in the vicinity of monitoring wells MW-1 and MW-2. The injection point layout is below.
COGAC™ Remedial Injection Results
As shown on the following graphs and table, dissolved petroleum hydrocarbon concentrations decreased to below laboratory detection limits after three post groundwater monitoring events at monitoring wells MW-1 and MW-2. 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 the site.