Activated Carbon is New to In-Situ Remediation

In the past couple of years in Canada, specially formulated activated carbon (AC) based remedial amendments have effectively contained and treated petroleum hydrocarbon and chlorinated solvent plumes.

Three brief case studies are presented in this article showcasing the power of activated carbon during in-situ remediation applications.

From the Vertex Vault:

Activated Carbon – What It Is and How It Works

Treating A Plume with One Injection

The great benefit of using AC-based remedial amendments during in-situ remediation is remedial objectives can be achieved in a single injection. Developing a detailed conceptual site model is critical to achieve this high level of performance. Product selection is also critical. For some AC-based formulations, sufficient carbon dosing is challenging to achieve because of the low concentration of carbon provided in the mixture. Effective remediation occurs when the correct amount of activated carbon is applied together with a mechanism for contaminant destruction.

In the case studies below, AC formulations known as Trap and Treat® were selected because the injected slurry contains a high dosing of activated carbon for effective contaminant adsorption along with amendments for subsequent degradation of those contaminants.

Case Study # 1: Chlorinated Solvents Along a Sewer Line

At a dry cleaning facility, chlorinated solvents were detected in groundwater adjacent to a sanitary sewer line and were threatening to migrate off site. This is a fairly common problem at commercial properties that formerly housed on-the-premises dry cleaning facilities.

Parameter MW-Deep

Max. Conc. (µg/L)

MW-Shallow

Max. Conc. (µg/L)

PCE 4,680 3,410
TCE 4.0 5.0
cDCE <0.50 <0.50
VC <0.20 <0.20
Total 4,684 3,415

To initiate degradation, a hydrovac truck was first used to expose the sewer line. Temporary direct push rods were then advanced to inject zero valent iron (ZVI) into and below the bedding of the sewer line to form a linear Permeable Reactive Barrier (PRB).

Four months after the ZVI injections (the green dashed line in the graphs below), the original parent compounds were reduced below site criteria in both the shallow and deep sampling locations. The deep sampling location exhibited excellent degradation of the PCE; however, breakdown compounds were reported at the shallow sampling location. This can be an unintentional side effect of the degradation of chlorinated solvents when insufficient contact or residence time is allowed with the ZVI – in this case possibly due to a higher than anticipated groundwater flow velocity in the granular sewer bedding material.

Vertex VOC Concentrations MW-Deep Before BOS100 Vertex VOC Concentrations MW-Shallow Before BOS100

 

 

To ensure the more immediate protection of the downgradient property boundary our client asked us if we could ramp up the treatment timeline.  We decided to inject the Trap and Treat® product BOS 100®.

The Trap and Treat® product BOS 100® is an activated carbon based substrate impregnated with iron. It serves the dual functions of (i) rapidly adsorbing contaminants from the groundwater thus preventing their continued migration and then (ii) degrading the contaminants in place using chemical reduction. The chart below shows the most recent groundwater data for the site, indicating both the parent and daughter compounds of this solvent plume are now effectively eliminated from the groundwater.

Vertex VOC Concentrations MW-Deep After BOS100 Vertex VOC Concentrations MW-Shallow After BOS100

 

 

The BOS100® trapped and treated the parent product PCE and the breakdown products, TCE, cisDCE and vinyl chloride.

Case Study # 2: Chlorinated Solvents at a Commercial Property in Guelph

Historic dry cleaning operations were suspected to be the cause of chlorinated solvent impacts in the groundwater within a native silty sand unit. The impacts affected approximately 40 m3 in the saturated zone. Vertex mobilized to the site for a one day injection. Again the Trap and Treat® BOS product 100® was selected for the job. A total of only 190 kg of BOS 100® was injected as a 9% slurry. All contaminants met site criteria within weeks of the single application, and continue to remain below the MOECC Standard months after the injection. Here’s a table of the results:

Parameter MOECC
Standard (
µg/L)
Pre-Inj. Conc. (µg/L) Post BOS 100 Inj. (µg/L)
7 Weeks 11 Weeks
PCE 17 40 11.7 11.6
TCE 5 2.2 2.2 2.8
cDCE 17 8.1 2.6 3.0
VC 1.7 <0.50 <0.50 <0.50
Totals 50.3 16.5 17.4
Reduction (%) 67% 65%

The property was refinanced based upon the consultant’s clean post-remediation report.

Case Study # 3: Chlorinated Solvents at a Commercial Property in London

At a site in London with historic dry cleaning operations, chlorinated solvents had impacted the groundwater. A variety of technologies (source area excavation, oxidant injections, pump and treat) had removed much of the contaminant mass both inside and outside of the building.

However, after a number of years, residual impacts still affected approximately 130 m3 in the saturated zone:

VOC Concentrations London Site Before BOS100

 

Vertex mobilized to the site for three days of injections where a total of 450 Kg of BOS 100® was injected as a 10% slurry.

The results were immediate and dramatic:

VOC Concentrations London Site After BOS100

 

Conclusions

Chlorinated solvents in the groundwater are quickly adsorbed by activation carbon injections. Solvent contamination is often eliminated from the groundwater within days and weeks. The subsequent treatment of the adsorbed contaminants via chemical reduction using the iron impregnated within the BOS 100® matrix eliminates the contaminants in the subsurface ensuring that the carbon does not become saturated and lose effectiveness over time.

The keys to success:

  1. Development of a strong conceptual site model
  2. Ensure sufficient dosing of activated carbon by using a concentrated slurry form
  3. Deliver to specific and highly targeted lateral zones and vertical horizons (where contaminant mass resides)
  4. Use an activated carbon impregnated with additional treatment additives to ensure contaminant destruction as well as adsorption

If you have a lingering chlorinated solvent issue at a site, by following these design rules, you and your client should be rewarded with a high level of sustained remediation success over a very short timeframe.

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Until next time: Excellence is Your Choice!

Bruce, Kevin, Mike, Nathan, Pat, Kyle & the rest of the Vertex Team!