CASE STUDY: Gasoline with BTEX in Mississauga, Ontario

Protecting employee health and the environment using hydraulic containment at an active gas station.

Background

The site of an active gas station with a fast-food drive-through in an urban area, required remediation to address residue contamination from historical gasoline leaks and spills. The small, heavily trafficked site required a discrete approach, based within a compact, self-contained infrastructure.

Location: Mississauga, Ontario, Canada

Client: Commercial Retailer

Duration: Ongoing, 4+ years

Project Value: $7,000 CDN per year

Geology: Fill & Weathered Shale

Plume Size: 200 m2

Approach

A previous contractor had initiated the project but they were unable to continue overseeing it. IRSL earned the project renewal directly with the landowner based on their past history, and their ability to effectively analyse the situation and recommend a sound solution.

Groundwater Pump & Treat System

To mitigate the dissolved phase plume, IRSL analysed the situation and existing system and then designed, implemented, maintained, and continues to optimize a pump & treat system for the capture and treatment of Gasoline and BTEX compounds in the groundwater using a compact infrastructure.

Analysis & Optimization

The existing system was reviewed, tested, and analyzed for its effectiveness, from both a technical and cost perspective. The results of the testing program revealed that the existing system was undersized at key points, which resulted in potential discharges of non-treated groundwater into the environment. IRSL redesigned and tested the modified system to ensure that no unauthorized discharges occurred.

Treatment System

The redesigned Pump & Treat system consisted of one well instrumented with a submersible pump, from which water was pumped into an above-ground system. The system was less than 12 m2 and housed in a sound-proofed, secure container, in a small shed, creating a very small footprint. Recovered groundwater was treated to levels below the regulatory limits and disposed of into the sanitary sewer system, as per an agreement with the municipality.

Treatment Train

To remove the Petroleum Hydrocarbons from the groundwater, IRSL used a variety of well-proven and accepted methodologies, including:

  1. Sediment Tank: To remove large particles.
  2. Particle Filters: To remove fine particles.
  3. Activated Carbon: To remove the Gasoline, BTEX, and other organic contaminants.
Gas Station Remediation System, Mississauga, Ontario

Sand, Particulate and Green Filters

Extracted groundwater is filtered through various sand, particulate or “green” filters to remove fine particles that can plug down gradient filters and media as well as removing some contaminants such as iron and lead. IRSL provides technical advice to our clients on which filters are most effective for their application. Various types of filters can be utilized, including:

  • Canister
  • Sand
  • Bag
  • Organoclay
  • Chemical filters, such as Greensand

Activated Carbon

Composed of black granules of bituminous coal, wood, nutshells or other carbon-rich materials, Granular Activated Carbon (GAC) can treat a wide range of contaminants dissolved in groundwater, such as fuel oil, solvents, polychlorinated biphenyls (PCBs), dioxins, and other industrial chemicals, as well as radon and other radioactive materials. As contaminated water or air flows through the activated carbon, the contaminants are chemically bound, or sorbed, to the surface of the carbon, removing them from the water or air. Various types and grades of GAC exist, including virgin and regenerated. IRSL aids our clients in determining which carbon type and carbon material is best for their application.

Challenges

  • Detailed analyses of the existing system were required in a short time-frame to ensure plume capture and confirm no adverse impacts to down-gradient human and ecological receptors.
  • The small parking lot of the active station and drive-through required a very small footprint.
  • The busy urban location required completing low-noise impact assessments.
  • The system required year-round operation, necessitating winterization to protect the equipment and piping against freezing in sub-zero temperatures.

Results

  • System testing and modifications resulted in no further unauthorized discharges to the environment.
  • The modified treatment system met the discharge criteria.
  • Over the course of the project, operating and maintenance costs have decreased relative to inflation.

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