Environmental team oversees hazardous flooring removal at Powell Middle School

By: Tim Mulholland
10 May 2017

As part of recent major facility renovations at Powell Middle School (Powell, WY), approximately 10,500 square feet of polyurethane flooring on the gymnasium slab were to be removed. This isn’t normally a big deal, but unfortunately, the flooring contained mercury vapor, having been used by the manufacturer as a catalyst during the installation process. Yes, this is correct: mercury vapor was actually used as a catalyst during the foam-blowing agent process. CTA’s Environmental Services team was engaged to complete the following actions:

  • Characterization of the flooring and associated material for disposal;
  • Preparing specifications for an abatement contractor to remove the flooring in a safe and efficient manner;
  • Development of methodology for determining post-abatement clearance criteria to ensure the health and safety of children reentering the space;
  • Inspection of the abatement contractor’s containment and negative pressure system;
  • Coordination of disposal of the flooring and associated materials as a hazardous waste; and
  • Collection of data necessary to demonstrate any residual mercury vapor in the concrete slab will not create unacceptable risk to occupants of the school.

Our team determined the flooring was a characteristically hazardous waste, and required special handling and disposal at an approved treatment, storage, and disposal facility (TSD) in Mountain View, ID. It was also determined the mercury vapors had migrated into the concrete slab, requiring the top few millimeters to be removed using a steel-shot media blaster with concrete dust recovery system. It was anticipated the mercury vapors would volatilize once the concrete was pulverized, and they were recovered using a high-flow/vacuum recovery system. The concrete dust, however, was also deemed hazardous waste and similarly required disposal in Idaho.

The unique nature of this project required CTA’s team to develop criteria and sampling methods to demonstrate there is no long-term risk from residual mercury vapor exposure to students and faculty. During oversight of the abatement, it was determined the initial clearance criterion was lower than background mercury vapor concentration. We used a combination of a real-time mercury vapor meter and passive “badge” sample media to estimate short- and long-term volatilization of residual mercury vapor from the concrete slab. The combination of mercury badge and real-time monitoring data demonstrated the mercury had been abated and the floor leveling compound was an effective vapor barrier, preventing risk to mercury exposure above background concentrations.

The project called upon the professional expertise of team members Tim Mullholland, PE; Keith Cron, CIH; Allan Brummett; and Raelynn Meissner, PE. After the floor was safely removed, the rest of the project was smooth sailing. Powell’s gym reopened for school this year!

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