CASE STUDY: CTET Remediation near Calgary, Alberta

Using Enhanced Anaerobic Bioremediation with Emulsified Vegetable Oil to remediate CTET from Silty Sand.

Background

Under a busy parking lot surrounded by multi-tenant residential buildings just outside of Calgary, Alberta, a lingering carbon tetrachloride (CTET) groundwater plume required remediation. The former site of an oil industry component manufacturer that had used a degreasing chemical wash as part of their manufacturing process, the plume had been identified in the 1980’s. Since then, the contamination had been addressed with limited success using a variety of remediation methods, including pump & treat, air sparging, and soil vapour extraction.

Based on pressure from a regulatory agency, the landowner retained IRSL to develop and implement an in-situ program to address the remaining dissolved phase impacts within the very fine-grained silty sand aquifer. The active, populated location required a discrete solution with a minimal environmental footprint.

Location: Calgary, Alberta Canada

Client: Industrial

Duration: 3 weeks

Geology: Silty Sand

Plume Size: Approximately 750 m2

Approach

An environmental consultant hired by the landowner characterized the site and determined that the groundwater was still impacted with carbon tetrachloride (CTET). Located in a shallow aquifer, the CTET plume covered an area of approximately 750 m2 and penetrated the aquifer to approximately 2 m below the water table. IRSL was retained by the client based on their innovative design and successful approach at other sites impacted with chlorinated compounds.

In-Situ Anaerobic Bioremediation with Emulsified Vegetable Oil (Evo)

To treat the remaining dissolved phase impacts, IRSL designed a Direct Push Injection program that used Emulsified Vegetable Oil (EVO) to provide a carbon donor that would enhance the anaerobic bioremediation reactions already occurring within the 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. The injection points required a very small footprint, minimizing the impact on client operations, and ensuring their revenue streams were not affected.

Treatment

To remediate the carbon tetrachloride (CTET) within the groundwater to below the remedial targets, IRSL worked with the manufacturer of the donor solution to create the most effective formula to stimulate Anaerobic Bioremediation, based on site data input into their proprietary analytic equipment.

IRSL completed one injection of Emulsified Vegetable Oil (EVO) enhanced with nutrients and buffering agents:

  • EVO stimulated the natural attenuation reactions already occurring in the aquifer by providing a carbon donor to the native bacteria, which fed on the contaminants, breaking them down into harmless by-products.
  • Nutrients helped the native bacteria to build cell mass, thereby overcoming limiting reactions.
  • Carbonate Buffering Reagent kept the pH of the system within the bacteria’s preferred range.

Enhanced Anaerobic Bioremediation

Enhanced Anaerobic Bioremediation creates conditions in which naturally occurring or injected micro-organisms, in the absence of oxygen, will feed on contaminants, breaking them down into less-toxic compounds and by-products such as chloride, elemental sulfur, hydrogen gas, methane, and sulfide.

Successful anaerobic bioremediation efforts must incorporate all of the necessary components:

  • An abundant supply of electron acceptors.
  • Nutrients for building cell mass.
  • Active cultures to spur on microbial growth.
  • Enzyme enhancements to increase bioavailabilty.

Emulsified Vegetable Oil (EVO)

In this anaerobic bioremediation technique, vegetable oil donates electrons to enhance the reductive dechlorination of the CTET and its daughter products by native bacteria into such harmless byproducts as ethene, chloride, and water.

Vegetable oil is a cost-effective slow-release electron donor with greater hydrogen release efficiency than other electron donors. Emulsification ensures small, uniform droplet sizes that distribute evenly throughout the plume.

Monitoring

Throughout the project, an independent consultant monitored the process and conducted a rigorous 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 non-homogenous, very fine-grained silty sand had limited previous remedial efforts and required a more robust remedial design.
  • Ensuring that a sufficient mass of electron donors was injected along with appropriate buffering and nutrient reagents required careful analysis and preparation.

Results

  • The remedial program was executed in three weeks.
  • The CTET was treated to below the remedial targets developed for the program.
  • Long-term monitoring indicated that the groundwater concentration remained below the remedial targets for the one-and-half years since remediation.

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