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2024-11_VAPOR MITIGATION COMPLETION_BF0001383 t-rem-vic2-24 · LB 1683 · 8/18/22 November 26, 2024 VIA EMAIL Steve Dunbar Fridley Investments LLC Willows Bend Senior Living LLC 323 Washington Ave N Ste 200 Minneapolis, MN 55401-2206 RE: Technical Assistance Letter: Completion of Vapor Mitigation for On-site Building Approval of RAP Implementation Report City of Fridley City Hall, 6455 University Ave NE, Fridley MPCA Site ID: BF0001383 Billing ID: 47406 Re-platted PIN: 14-30-24-31-0102 Dear Steve Dunbar: The Minnesota Pollution Control Agency (MPCA) staff in the Voluntary Investigation and Cleanup Program has been requested to provide confirmation that soil vapor assessment and vapor intrusion mitigation activities at a portion of the City of Fridley City Hall site, located at the address referenced above, have been successfully completed in accordance with MPCA’s Vapor Investigation and Mitigation Decision and Vapor Mitigation Best Management Practices documents. Specifically, this letter applies to the 6455 University Avenue parcel (the Site). The MPCA staff has reviewed the information submitted for the Site. The Site consists of three parcels (recently re-platted from 11 parcels) totaling 4.54 acres. From the 1940s until the mid-1960s, the eastern portion of the Site was used for residential purposes. The Site was used by the City of Fridley for various municipal services including a fire station, police station, indoor shooting range, jail, meeting hall, and government offices from 1952 until the buildings were demolished in 2019. Only the garages and indoor shooting range remained at the Site. Fridley Investments LLC recently redeveloped the Site into a senior living facility with one level of underground parking. The MPCA issued a No Association Determination to Fridley Investments LLC, dated May 21, 2020, contingent upon Fridley Investments LLC redeveloping the Site in accordance with an MPCA-approved response action plan (RAP). Based on data available to date, the Site appears to lie within a larger undefined area of soil vapor impacts that is currently under evaluation by the MPCA’s Site Assessment Program (MPCA Site ID SA0000787). A limited environmental investigation was completed at the Site in October 2018 to investigate potential impacts at the Site near two abandoned fuel oil tanks (Leak #8863). Five borings were advanced for the collection of soil and groundwater samples. One soil sample was collected and analyzed for volatile organic compounds (VOCs), polynuclear aromatic hydrocarbons (PAHs), and eight Resource Conservation and Recovery Act (RCRA) metals. Only petroleum-related VOCs were detected in the soil Steve Dunbar Page 2 November 26, 2024 samples and metals were within the range of typical background concentrations. One groundwater sample was collected and analyzed for VOCs and PAHs. Only petroleum-related VOCs and PAHs were detected in groundwater. Soil vapor samples were collected at six locations at the Site in June 2019 (non-heating season) and March 2020 (heating season) in the vicinity of the former fuel oil tanks. During the second round of sampling, two soil vapor samples were collected along the southern boundary of the Site to rule out possible impacts from a former drycleaner at the south-adjacent property. Several non-petroleum VOCs, including tetrachloroethene (PCE), were detected in soil vapor at concentrations less than the MPCA action level of thirty-three times (33X) their respective residential intrusion screening value (ISV). A Response Action Plan/Construction Contingency Plan dated October 29, 2020, was approved by the MPCA on January 29, 2021, for the redevelopment of the Site into a senior living facility. Five additional soil vapor samples were collected from locations beneath the proposed building footprint in March 2021 (heating season). Several non-petroleum VOCs, including PCE, were detected in soil vapor at concentrations greater than the MPCA action level of 33X their respective ISV. A RAP Addendum dated April 2, 2021, that described the installation plan for the vapor mitigation system in the Site building was approved on June 9, 2021. Vapor mitigation activities completed for the Site building are described in the Vapor Mitigation Response Action Plan Implementation Report prepared by Braun Intertec and dated February 28, 2023 (Implementation Report). An active sub-slab depressurization system was installed during construction of the new Site building. Post-mitigation confirmation sampling was completed in December 2022. Measurement of pressure differential and analysis of confirmation samples indicate that the vapor mitigation system in the Site building is working as designed. The Implementation Report is approved. The MPCA hereby confirms that the vapor assessment completed at the Site was conducted in accordance with MPCA’s Vapor Investigation and Mitigation Decision Best Management Practices and that vapor intrusion mitigation activities for the existing Site building, as described in the Implementation Report, were successfully completed in accordance with the MPCA-approved Response Action Plan dated October 29, 2020 and the RAP Addendum dated April 2, 2021 and the MPCA’s Vapor Mitigation Best Management Practices. To ensure ongoing protection against vapor intrusion, the vapor mitigation system in the Site building must be operated, monitored, and maintained in accordance with the Vapor Intrusion Mitigation System Operation and Maintenance Plan prepared by Braun Intertec and dated February 28, 2023. Due to the affirmative obligation to operate and maintain the vapor mitigation system, an Environmental Covenant was filed on November 12, 2024, in the office of the County Recorder in and for Anoka County, as document number 2425151.001. Please note that the Environmental Covenant requires submittal of an annual compliance report/letter by July 1 of each year to document the status and condition of the vapor mitigation system. The annual compliance report/letter should include supporting documentation and be sent via electronic mail to instcontrols.pca@state.mn.us. Please include the MPCA project name (City of Fridley City Hall site) and identification number (BF0001383) on the submittal. This determination is based on the building-specific vapor mitigation actions completed at the Site, as described in the Implementation Report. This letter does not address any conclusions or representations regarding future structures or changes in land use at the Site, which may create new potential exposure pathways for soil vapor contaminants. The MPCA recommends that future construction activities at the Steve Dunbar Page 3 November 26, 2024 Site (e.g., potential addition, new building, new utility trenches, etc.) be preceded by a soil vapor investigation within the footprint of the proposed construction area, so a vapor mitigation decision for the new feature can be made based on concurrent data. This letter does not address any conclusions or representations regarding soil or groundwater at the Site, or regarding petroleum-related VOCs that may have been detected in soil vapor. Petroleum contamination detected at the Site is under the oversight of the MPCA’s Petroleum Brownfield Program. Please be advised that the determination made in this letter is subject to the disclaimers found in Attachment A and is contingent on compliance with the terms and conditions set forth herein, including ongoing operation, monitoring, and maintenance of the vapor mitigation system in the Site building, as required by the Environmental Covenant. If you have any questions about the contents of this letter, please contact Shanna Schmitt, Hydrogeologist, at 651-757-2283 or by email at shanna.schmitt@state.mn.us. Sincerely, Amy K. Hadiaris This document has been electronically signed. Amy K. Hadiaris, P.G. Supervisor Voluntary Investigation and Cleanup Unit Remediation Division Attachment AKH/SS:df cc: Mark Keefer, Braun Intertec, (electronic) Jonelle Hubbard, Anoka County Environmental Services (electronic) Melissa Moore, City of Fridley (electronic) Christopher Goscinak, MPCA Site Assessment Program (electronic) Attachment A Page 1 of 1 Disclaimers City of Fridley City Hall MPCA Site ID: BF0001383 1. Reservation of authorities The MPCA Commissioner reserves the authority to take any appropriate actions with respect to any release, threatened release, or other conditions at the Site. The MPCA Commissioner also reserves the authority to take such actions if the voluntary party does not proceed in the manner described in this letter or if actions taken or omitted by the voluntary party with respect to the Site contribute to any release or threatened release or create an imminent and substantial danger to public health and welfare. 2. No MPCA assumption of liability The MPCA, its Commissioner, and staff do not assume any liability for any release, threatened release, or other conditions at the Site or for any actions taken or omitted by the voluntary party with regard to the release, threatened release, or other conditions at the Site, whether the actions taken or omitted are in accordance with this letter or otherwise. 3. Letter based on current information All statements, conclusions, and representations in this letter are based upon information known to the MPCA Commissioner and staff at the time this letter was issued. The MPCA Commissioner and staff reserve the authority to modify or rescind any such statement, conclusion, or representation and to take any appropriate action under the Commissioner’s authority if the MPCA Commissioner or staff acquires information after issuance of this letter that provides a basis for such modification or action. 4. Disclaimer regarding use or development of the property The MPCA, its Commissioner, and staff do not warrant that the Site is suitable or appropriate for any particular use. 5. Disclaimer regarding investigative or response action at the property Nothing in this letter is intended to authorize any response action under Minn. Stat. section 115B.17, subd. 12. 6. This approval does not supplant any applicable state or local stormwater permits, ordinances, or other regulatory documents.