Urgent vapor mitigation system installation, commissioning, and monitoring for combined restaurant/grocery store.
PROJECT SUMMARY
An approximate 6,250 square foot commercial building is located at 211 Jacob Street, Sturgis, Michigan. In January 2021, based upon available site data (i.e., soil gas and indoor air analytical results), EGLE determined that an unacceptable VIAP exposure risk to building occupants existed and required immediate emergency response action. In January and February 2021 HMA designed and installed a sub-slab depressurization system (SSDS) to mitigate indoor air inhalation exposure risk from volatile organic compounds (VOCs) that would otherwise occur from subsurface soil gas intrusion to the building indoor air. The SSDS consists of five suction pits (SP-1 to SP-5) powered by three radon type fans and was commissioned on February 11-12, 2021. On March 10-11, 2021, HMA measured vacuum pressure at seven permanent vapor monitoring ports (VP-20-01 through VP-20-07) and collected six indoor air samples as post-installation verification of SSDS operation. The SSDS verification activities demonstrated that EGLE recommended vapor pressure (-0.02 inches water column) is maintained throughout the entire building footprint. The VOC concentrations for the March 10, 2021, indoor air samples were less than laboratory method detection limits (MDLs) and/or EGLE RIASLs. Between January 25, 2021, and March 11, 2021 (seven weeks) HMA completed the design, installation, and verification of an SSDS vapor intrusion mitigation system (VMS) to successfully mitigate VIAP exposure risk.
PROJECT HIGHLIGHTS
• 6,250 ft2 slab-on-grade commercial building; restaurant and grocery.
• Trichloroethylene (TCE) sub-slab / indoor air sample concentrations exceed Michigan Department of Environment, Great Lakes and Energy (EGLE) volatilization to indoor air pathway (VIAP) screening levels.
• Collaborate with building owner on vapor mitigation system (VMS) design.
• Pressure field extension (PFE) diagnostic testing for VMS design.
• VMS Design: five suction pits / three mitigation fans; 200 feet of PVC piping, and 200 feet of electrical wiring.
• PFE testing verified full sub-slab depressurization to 0.02 inches of water column (WC).
• 30-day post-VMS install testing: TCE was not detected in 24-hour SummaTM canister indoor air samples collected from five locations in the building.
• One–year operation, maintenance and monitoring (OM&M) to verify VMS sustains PFE metric beneath slab at –0.02 inches WC, and TCE indoor air concentrations are less than EGLE Nonresidential Recommended Interim Action Screening Levels (RIASLs).
