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September 18, 2024 City Council – City of St. Anthony Village Page 2 of 4 Reference: Environmental Conditions Summary – Proposed Tibyan Community Center, 2401 Lowry Avenue NE, St. Anthony, Minnesota (the Site) In February and March 2018, a paired sub-slab soil vapor and indoor/outdoor air sampling event was performed in support of a completed pathway evaluation, which was an acceptable soil vapor risk assessment strategy at that time. Five sub-slab soil vapor samples and five paired indoor air samples were collected from within the building footprint, five external soil vapor samples were collected from locations within the parking lot, and an ambient air sample was collected from outside of the building. Soil vapor beneath the parking lot was impacted by numerous VOCs, including PCE and TCE at concentrations greater than 33X the MPCA’s industrial EISV. Sub-slab soil vapor collected from within the building footprint had TCE at concentrations greater than 33X the MPCA’s industrial ISV. Soil vapor was also impacted by elevated levels of dichlorodifluoromethane and cis-1,2-DCE, however an ISV had not been established for dichlorodifluoromethane or cis-1,2-DCE at the time. Indoor air samples contained contaminants of concern in concentrations below the MPCA’s industrial ISVs. In April 2018, November 2018, May 2019, and June 2020 subsequent seasonal sampling events were performed in support of the completed pathway evaluation. For each sampling event, five sub-slab soil vapor samples and five paired indoor air samples were collected from within the building footprint and an ambient air sample was collected from outside of the building. Sub-slab soil vapor was impacted by TCE at concentrations greater than 33X the industrial ISV and PCE was detected in sub-slab soil vapor at concentrations less than 33X the industrial ISV but greater than 33X the residential ISV. Sub-slab soil vapor was also impacted by trans-1,2-DCE at concentrations less than the industrial ISV and by cis-1,2-DCE. Indoor air concentrations were again less than the MPCA’s industrial ISV. As a result of the completed pathway evaluation, an active vapor mitigation system was recommended to be installed in any future occupied Site building. Subsequent investigations were completed at the Site in June 2023 to further delineate soil and groundwater impacts around the Site. Soil investigation activities included the advancement of nine push-probe borings for the collection of 11 soil samples and four groundwater samples. Soil analytical testing detected RCRA metal and PAH impacts that did not exceed their respective SRVs and SLVs. DRO was detected below the unregulated fill criteria. VOC analysis detected concentrations of PCE and TCE above its SLV in samples collected from the northern half of the Site. Groundwater analytical results from temporary wells identified the presence of PCE, TCE, and cis-1,2-DCE above their respective HRLs or Health Based Values (HBVs) in borings collected from the north and east portions of the Site. Copies of the investigation reports detailed above can be made available upon request. 2024 Indoor Air Sampling Event On behalf of Tibyan Community Center, Stantec completed indoor air sampling in August 2024 to assess indoor air conditions at the Site building following a period of vacancy. The indoor air sampling event consisted of the placement of three laboratory-provided summa canisters equipped with a 24-hour flow controller. The three samples were placed in the basement in the east and west mechanical rooms, both located in the southwest portion of the Site building, and the main lobby area located in the northeast portion of the building. Sample results identified PCE in a concentration exceeding its MPCA industrial ISV in the main lobby area. PCE was also detected in concentrations exceeding its MPCA residential ISV in the other two samples, and TCE was detected in a concentration exceeding its MPCA residential ISV in the main lobby. Indoor air sample locations are shown on Figure 3, and a summary table is included as Table 1. A vapor intrusion building survey form is included as Attachment A. The full laboratory report can be made available upon request. 73