At the July 18, 2023 City Council meeting, representatives from PBS Engineering and Environmental (PBS) provided an overview of the environmental assessment work performed at City Hall and reviewed the findings. Here’s what was presented:
Testing Methods and Results
Following the initial asbestos testing, the City hired PBS to advise staff, conduct more intensive testing, and ensure that industry best practices were followed in further detection and risk mitigation efforts. Between late April and early July, PBS performed three primary types of tests: air quality, settled dust, and bulk material testing, with hundreds of samples collected across all test types.
The intent of air sampling is to screen interior air for potential asbestos fibers. Air samples were collected from locations throughout the building, using high-volume air sampling pumps and analyzed using the NIOSH 7402 method, which uses Transmission Electron Microscopy (TEM) and reports findings in concentrations of fibers per cm3. No asbestos fibers were identified in the collected air samples.
The intent of this sampling is to evaluate surface dust in the building and mechanical system for potential asbestos content. PBS collected settled dust samples at representative locations throughout the interior of City Hall and inside the HVAC system. Each sample was collected using an air sampling pump to draw dust from a 100 cm2 area.
Samples were analyzed using the ASTM D 5575-09 method, which uses Transmission Electron Microscopy (TEM) and reports findings in concentrations of structures per square centimeter (s/cm2). Findings are reported based on the size of any asbestos identified, grouped by between 0.5 and 5 microns, and those larger than 5 microns.
‘Background levels’ of asbestos structures in accumulated dust range from an average of 1,000 s/cm2 in non-industrial areas to 10,000 s/cm2 in cities and industrial areas where asbestos materials are common. Levels above 10,000 s/cm2 are generally considered to be “above background” in any geographical location. There are no regulatory thresholds for the amount of asbestos in surface dust.
Asbestos concentrations in excess of 10,000 s/cm2 were identified in six of the samples, all of which were associated with the HVAC system.
Bulk Asbestos Sampling
PBS took 84 samples from various materials for the presence of asbestos. This has been conducted to confirm asbestos content in select building materials.
Samples were analyzed according to either EPA Method 600R-93/116 using Polarized Light Microscopy (PLM) or EPA Method 600R-93/116 TEM Bulk Semi-Quantitative.
In addition to the various flooring and adhesive materials that tested positive for the presence of asbestos, three bulk samples taken from HVAC filters contained trace amounts of asbestos, and two window-glazing putty samples tested positive.
Limitations on Testing and Inspection
One goal of this wide-ranging testing was to create a comprehensive survey of conditions inside the HVAC system. However, field analysis found that many of the oldest ducts are encapsulated behind heavy plastic sheeting and fiberglass batt insulation and/or multiple layers of ceiling material. Accessing these areas for testing will require coordinated and costly deconstruction of multiple building systems including but not limited to electrical, data and low-voltage cabling, plumbing, ceiling grid, and insulation. The testing inside the HVAC system was taken as far as it could but was halted due to limited access to the remaining areas.
In conjunction with the targeted HVAC testing, a building-wide “Good Faith Inspection” was conducted on June 27, 2023 to detect, identify, and catalog any unknown asbestos-containing materials. The goal of the inspection was a full-building analysis, but the scope of the investigation was also limited due to the inaccessibility of much of the attic and roof structure of the building. No previously unknown asbestos-containing materials were found in the areas that were accessible for surveying.
While the floor tiles and adhesive found in the basement mechanical room alerted staff to the asbestos issue and prompted extensive testing in the building, these items are not likely to be the sole source of asbestos detected in portions of the HVAC system. Additional sources of asbestos contamination have not been definitively identified, and likely will not be uncovered by further testing. Based on the varying levels and locations of asbestos identified through the testing completed to date, PBS consultants believe there is a high probability that one or more sources of contamination contributed to the issue over the life of the building. Further, there is a high likelihood that the original asbestos-containing materials were removed during a previous renovation in the late 1980s.
Abatement, which is the removal of contaminated materials and equipment by a specialized contractor, has only been completed in a limited area of the basement of City Hall. Specifically, the basement mechanical room floor with asbestos containing broken tiles and adhesive was abated by a licensed contractor in mid-May, with post-abatement sampling of the floor confirming that there are no longer detectable traces of asbestos present. The HVAC system at City Hall remains unabated and turned off. Unless it is abated, it must remain off.
Potential Solutions to Re-Occupy City Hall
Northwest Studio, the City’s architect team, presented two preliminary scenarios to the City Council to re-occupy City Hall:
The first scenario was a full re-occupancy of City Hall. This work would require abatement of the floor tiles in the basement mechanical room, replacement of the HVAC hydronic and ventilation system, and the replacement of various building infrastructure required by replacement of the HVAC system (ceilings, light fixtures, cabling, etc.). The preliminary cost estimate to re-occupy City Hall under this scenario is $10 million with an estimated timeline of nearly two years to complete the work. This cost estimate does not include full abatement costs or softs costs such as design, engineering, and project management costs.
The second scenario was to investigate the possibility of re-occupying only the Police Department areas of City Hall for seven years while longer-term options were investigated. The team looked at partitioning the existing Police Department spaces from the remainder of the City Hall building, abating those spaces, removing the existing HVAC system, and installing a contemporary system to serve this occupancy. The preliminary cost estimate to abate and re-occupy the Police Department portion of City Hall is over $4 million with an estimated timeline of 12 to 18 months to complete the work. This cost estimate does not include full abatement costs or softs costs such as design, engineering, and project management costs.
Upon learning of the initial cost estimates to abate and re-occupy the City Hall building, and in consideration of the age and condition of the building, Councilmembers indicated during discussions at the July 18, 2023 City Council meeting that the costs to re-occupy City Hall outweighed the benefits of re-opening the building.
At the July 18, 2023 City Council meeting, representatives from PBS Engineering and Environmental (PBS) provided an overview of the environmental assessment work performed at City Hall and reviewed the findings. Here’s what was presented:
Testing Methods and Results
Following the initial asbestos testing, the City hired PBS to advise staff, conduct more intensive testing, and ensure that industry best practices were followed in further detection and risk mitigation efforts. Between late April and early July, PBS performed three primary types of tests: air quality, settled dust, and bulk material testing, with hundreds of samples collected across all test types.
The intent of air sampling is to screen interior air for potential asbestos fibers. Air samples were collected from locations throughout the building, using high-volume air sampling pumps and analyzed using the NIOSH 7402 method, which uses Transmission Electron Microscopy (TEM) and reports findings in concentrations of fibers per cm3. No asbestos fibers were identified in the collected air samples.
The intent of this sampling is to evaluate surface dust in the building and mechanical system for potential asbestos content. PBS collected settled dust samples at representative locations throughout the interior of City Hall and inside the HVAC system. Each sample was collected using an air sampling pump to draw dust from a 100 cm2 area.
Samples were analyzed using the ASTM D 5575-09 method, which uses Transmission Electron Microscopy (TEM) and reports findings in concentrations of structures per square centimeter (s/cm2). Findings are reported based on the size of any asbestos identified, grouped by between 0.5 and 5 microns, and those larger than 5 microns.
‘Background levels’ of asbestos structures in accumulated dust range from an average of 1,000 s/cm2 in non-industrial areas to 10,000 s/cm2 in cities and industrial areas where asbestos materials are common. Levels above 10,000 s/cm2 are generally considered to be “above background” in any geographical location. There are no regulatory thresholds for the amount of asbestos in surface dust.
Asbestos concentrations in excess of 10,000 s/cm2 were identified in six of the samples, all of which were associated with the HVAC system.
Bulk Asbestos Sampling
PBS took 84 samples from various materials for the presence of asbestos. This has been conducted to confirm asbestos content in select building materials.
Samples were analyzed according to either EPA Method 600R-93/116 using Polarized Light Microscopy (PLM) or EPA Method 600R-93/116 TEM Bulk Semi-Quantitative.
In addition to the various flooring and adhesive materials that tested positive for the presence of asbestos, three bulk samples taken from HVAC filters contained trace amounts of asbestos, and two window-glazing putty samples tested positive.
Limitations on Testing and Inspection
One goal of this wide-ranging testing was to create a comprehensive survey of conditions inside the HVAC system. However, field analysis found that many of the oldest ducts are encapsulated behind heavy plastic sheeting and fiberglass batt insulation and/or multiple layers of ceiling material. Accessing these areas for testing will require coordinated and costly deconstruction of multiple building systems including but not limited to electrical, data and low-voltage cabling, plumbing, ceiling grid, and insulation. The testing inside the HVAC system was taken as far as it could but was halted due to limited access to the remaining areas.
In conjunction with the targeted HVAC testing, a building-wide “Good Faith Inspection” was conducted on June 27, 2023 to detect, identify, and catalog any unknown asbestos-containing materials. The goal of the inspection was a full-building analysis, but the scope of the investigation was also limited due to the inaccessibility of much of the attic and roof structure of the building. No previously unknown asbestos-containing materials were found in the areas that were accessible for surveying.
While the floor tiles and adhesive found in the basement mechanical room alerted staff to the asbestos issue and prompted extensive testing in the building, these items are not likely to be the sole source of asbestos detected in portions of the HVAC system. Additional sources of asbestos contamination have not been definitively identified, and likely will not be uncovered by further testing. Based on the varying levels and locations of asbestos identified through the testing completed to date, PBS consultants believe there is a high probability that one or more sources of contamination contributed to the issue over the life of the building. Further, there is a high likelihood that the original asbestos-containing materials were removed during a previous renovation in the late 1980s.
Abatement, which is the removal of contaminated materials and equipment by a specialized contractor, has only been completed in a limited area of the basement of City Hall. Specifically, the basement mechanical room floor with asbestos containing broken tiles and adhesive was abated by a licensed contractor in mid-May, with post-abatement sampling of the floor confirming that there are no longer detectable traces of asbestos present. The HVAC system at City Hall remains unabated and turned off. Unless it is abated, it must remain off.
Potential Solutions to Re-Occupy City Hall
Northwest Studio, the City’s architect team, presented two preliminary scenarios to the City Council to re-occupy City Hall:
The first scenario was a full re-occupancy of City Hall. This work would require abatement of the floor tiles in the basement mechanical room, replacement of the HVAC hydronic and ventilation system, and the replacement of various building infrastructure required by replacement of the HVAC system (ceilings, light fixtures, cabling, etc.). The preliminary cost estimate to re-occupy City Hall under this scenario is $10 million with an estimated timeline of nearly two years to complete the work. This cost estimate does not include full abatement costs or softs costs such as design, engineering, and project management costs.
The second scenario was to investigate the possibility of re-occupying only the Police Department areas of City Hall for seven years while longer-term options were investigated. The team looked at partitioning the existing Police Department spaces from the remainder of the City Hall building, abating those spaces, removing the existing HVAC system, and installing a contemporary system to serve this occupancy. The preliminary cost estimate to abate and re-occupy the Police Department portion of City Hall is over $4 million with an estimated timeline of 12 to 18 months to complete the work. This cost estimate does not include full abatement costs or softs costs such as design, engineering, and project management costs.
Upon learning of the initial cost estimates to abate and re-occupy the City Hall building, and in consideration of the age and condition of the building, Councilmembers indicated during discussions at the July 18, 2023 City Council meeting that the costs to re-occupy City Hall outweighed the benefits of re-opening the building.
March 3, 2026 packet materials here: https://www.mercerisland.gov/citycouncil/page/city-council-regular-hybrid-meeting-59
January 16, 2026 packet materials found here: https://www.mercerisland.gov/citycouncil/page/city-council-special-hybrid-meeting-planning-session-2
March 3 2026 - Results of City Facilities Survey Presentation (2.68 MB) (pdf)