CASE STUDY: PFOA and PFOS Remediation in Silty Sand

Using Direct Push Technology to inject Liquid Activated Carbon and Persulphate to remediate residual groundwater impacts.

Background

Along the shore of Lake Ontario on the west side of Toronto, the industrial site of a former fabric coating manufacturer required remediation to remove residual perfluorinated compounds in the groundwater, including perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA). These emerging compounds of concern have been recognized as potentially carcinogen. Treatment of groundwater impacted by PFOS and PFOA is still evolving. The landowner required an expedient solution in order to complete the sale of the property.

IRSL, in collaboration with their suppliers, developed a remedial program to successfully address the dissolved phase plume while minimizing rebound and overcoming challenges associated with the very short remedial timeframe and limited site characterization.

Location: Toronto, Ontario

Client: Industrial

Duration: 1 week

Geology: Silty Sand

Plume Size: Approximately 350 m2

Approach

An environmental consultant hired by the landowner characterized the site and determined that the groundwater was impacted with perflourinated compounds. A PFOS and PFOA plume in the shallow aquifer covered an area of approximately 350 m2. IRSL was retained by the client based on their innovative design and successful approach at other sites impacted by emerging compounds of concern like PFOA and PFOS.

In-Situ Adsorption and Chemical Oxidation using Liquid Activated Carbon and Persulphate

To treat the remaining dissolved phase impacts, IRSL designed a Direct Push Injection program that used PlumeStop® Liquid Activated Carbon™ and Persulphate activated with hydrogen releasing compound to stimulate adsorption and chemical oxidation of the impacts in the shallow, silty sand aquifer.

Analysis

To develop an optimal injection design, IRSL used their proprietary analytical and numerical models, which incorporated contaminant concentrations, groundwater flow rates, reaction rates, temperature and inorganic parameters, within the subsurface. Through this process, they discovered the required mass and injection pattern that led to the successful remediation of the remaining impacts.

Construction

Based on their analysis, IRSL created and implemented a design that covered the groundwater plume while minimizing the possibility of rebound.

Direct Push Technology: To ensure coverage of the plume laterally and vertically, IRSL used Direct Push Technology over a 3 m grid with discrete vertical intervals to create a reactive zone.

Treatment

IRSL completed one injection of a combination of PlumeStop Liquid Activated Carbon and Persulphate:

  • Liquid Activated Carbon was injected into areas of lower PFO dissolved mass.
  • Liquid Activated Carbon plus Persulphate was injected into areas of higher PFO dissolved mass.

Adsorption

The PlumeStop Liquid Activated Carbon allowed for the adsorption of the contaminants from the groundwater.

Chemical Oxidation

Upon activation, persulphate ions produce very powerful sulphate and other free radicals, which enhanced the oxidative destruction of perfluorinated compounds in the groundwater.

PlumeStop Colloidal Biomatrix

PlumeStop® liquid activated carbon™ is a relatively new, dispersible substrate, capable of rapidly capturing and dropping a range of groundwater contaminant concentrations in days to weeks, while effectively biodegrading them over time. Developed by REGENESIS, USA, PlumeStop allows remediation practitioners to achieve fast treatment of groundwater with a high degree of certainty that the contaminants are biologically degraded.

Rebounding

Perhaps the biggest challenge associated with oxidants in general, is the plateauing or “rebound” of contaminant levels above the remedial objective for the site. Often referred to as rebound, it usually results from diffusion of the contaminants from finer-grained layers and lenses, or the rock matrix, back into zones of higher hydraulic conductivity.

Monitoring

Throughout the project, an independent consultant monitored the process and conducted a Quality Assurance-Quality Control program. Their subsequent monitoring of the groundwater quality confirmed that the remedial goals had been reached within the target timeframe and budget.

Challenges

  • The very short remedial timeframe required a very expedient design and implementation.
  • As a relatively new compound of concern, the perfluorinated compounds required an innovative treatment solution.
  • The site characterization left geological and hydrogeological unknowns that necessitated a robust remedial design.

Results

  • The remedial program was executed in one week with one injection.
  • The PFOA was treated to below the remedial targets developed for the program.

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