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In-Situ PFAS Immobilization and Beyond; Resilient Corrective Actions Applied at a Suspected AFFF Site in Alpena, Michigan

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Virtual Event

Monday, February 6, 2023, 3 pm

Event Details

This is a past event.

Environmental Engineering Graduate Seminar

Leonard Mankowski, Vice President - Geology, WSP


Perfluorooctane sulfonate (PFOS) is one of several per- and poly-fluoroalkyl substances (PFAS) detected at elevated levels in soil and groundwater at a former tannery located along the Thunder Bay River in Alpena, Michigan (Site). Tannery operations ceased in 1950 and the Site buildings burned to the ground in 2005. Aqueous film forming foam (AFFF) use is suspected during the 2005 fire. Investigations of PFAS in soil, groundwater, surface water, and river foam were initiated at the Site in 2017. Near the former building, residual PFOS impacts in soil extend from the capillary fringe (0.5 feet below grade (ft bg) to the base of the shallow aquifer (up to 8 ft bg). PFAS-impacted groundwater in the source area migrates into the Site’s decaying stormwater infrastructure and is conveyed to the river. Seasonally, impacted groundwater vents to the ground surface and is then conveyed by ditches to municipal stormwater infrastructure, which is also discharged to the river.  The groundwater plume from the Site is expanding toward Lake Huron.

Resilient pilot tests/corrective actions to mitigate PFAS impacts to surface water and reduce available source contaminant mass to control the PFAS groundwater plume have included:


  • Benchtop study demonstrated PFAS effectively removed from Site groundwater using biochar (2017). Injection & Soil Mixing biochar pilot tests initiated (2018).
  • Benchtop isolated candidate PFAS degrading microbes from Site soil and groundwater (2020). Bioaugmentation pilot test with chemical enhancement (oxygen release compound; ORC) and solar-powered air sparge initiated (2021).
  • Stormwater mitigation via placement of biochar-filled booms in historical tannery stormwater infrastructure (2019) and a combination of paving and stormwater infrastructure upgrades (2021) to reduce PFAS loading to existing stormwater infrastructure 
  • Phytoremediation pilot test initiated with in-situ immobilization and bioaugmentation (2022). 


In-situ biochar applied via soil mixing reduced PFOS levels in groundwater from 2,130 nanograms per liter (ng/L) to 23.3 ng/L at 28 days and 179 ng/L (a 92% reduction) at 1 year. Less reduction is observed in short-chain PFAS (PFBA=39% and PFBS=57% at 1 year). Injection pilot test results indicate PFOS reductions of 35% to 100% in groundwater (varied by loading rate). Leachability tests indicate PFOS leaching in soil mixing decreased at 1-year by 79% (SPLP) to 99% (TCLP) at 1-year. 

Endemic microbes isolated from the Site demonstrated PFOS reductions of up to 70% with aeration at 8 weeks (bench top). Analyses indicate free fluoride is produced by two of the isolated candidate PFAS-degrading microbes. During the limited bioaugmentation and oxygenation pilot test PFOS levels decreased by over 50% in the microbe/oxygen treated area (through two weeks) but stalled when oxygen level dropped. Lessons learned are being applied in conjunction with phytoremediation to depress the water table, contain groundwater on the site and reduce PFAS concentrations in groundwater prior to plant uptake.


Leonard (Len) Mankowski is a Vice President - Geology at WSP with over 18 years of site characterization and remediation experience at contaminated Sites across Michigan and the Midwest.  His primary areas of expertise include innovative remedial investigation techniques; hydrogeologic and conceptual site model development; emerging contaminants; and conceptual remedial design/technology assessments. 

Len earned a Bachelor of Science degree in applied geophysics (1999) and a Master of Science in Geology from Michigan Technological University (2003) and was an instructor at Michigan Technological University prior to entering consulting.  Mr. Mankowski has published and/or presented several papers on applied, innovative characterization and remediation approaches. 

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