Tittabawassee River, Saginaw River & Bay Site 2020 Post-Flood Update for the CAG Virtual Meeting July 14, 2020 Mary Logan Joe Victory Todd Konechne U.S. EPA EGLE Dow Water was released to May 19, 2020 the Edenville Wixom Lake faster and Sanford Dams failed than Edenville dam was discharging ~ 5:45 PM Edenville Dam embankment failed That evening Sanford Dam breached and dam bank failed 2 Edenville Dam 3 Sanford Lake Edenville Dam 4 Sanford Dam and Lake Bridge photo by Kelly House https://www.bridgemi.com/michigan-environment-watch/see-dow-chemical-ponds-dioxin-cleanup-site-after-michigan-flooding 5 11,000 residents evacuated No deaths Exceptional planning & use of technology & social media Roads/Bridges washed out/closed 6 Sanford Dam 7 8 Sanford Mainstreet 9 Dow Midland Plant • The Dow Facility is not part of the Superfund assessment and cleanup, but we expect the CAG is interested in a brief post-flood update 10 Regulated Components of the Dow Facility • Dow’s Midland Plant Operations – Managed by Tittabawassee River, Saginaw River & Bay Superfund site – U.S. EGLE Under Part 111 of NREPA EPA AOC (CERCLA) • Management of various impacted media including • Legacy Dioxin contaminated sediments, banks, sediments, soils, groundwater, surface water floodplain 11 Dow Midland Facility Map 12 Waste Management Units/Corrective Action at Dow Midland Plant Managed under Part 111 of NREPA • Landfills - Leachate Collection (primarily VOCs, SVOCs) • Retention Ponds/Impoundments (Water and Sediment Management) • Groundwater – RGIS (VOCs - chlorobenzenes, chlorophenols, SVOCs, Metals, Pesticides, co-solvated dioxins, hydraulic gradient control) • Surficial Soils – Capped (Dioxins) • Wastewater Treatment Plant (Various waste streams) • 24 On-Site Monitoring Programs under the Part 111 License • Other On-Site Corrective Action Studies are Ongoing • Contingency Plans under Part 111 License were enacted during the flood 13 Dow’s Reported Actions • Throughout Dow worked with local and state authorities • Dow reported at least daily to EGLE • Dow’s reported timeline • May 18, 11:45 pm – MIOPS EOC initiated shutdown preparations • May 19, 6:00 pm – MIOPS EOC initiates final plant shutdown orders and personnel evacuation • May 20 – river crested at 35.05 feet (flood stage is 24 feet) • May 26 – plant declared safe for re-entry • Some of Dow’s reported actions • Employee accountability • WWTP continued to operate – this was a priority • Stormwater was managed • De-energized electrical to impacted areas • Impacted assets secured/ brought to safe state 14 • River crest at 615 ft AMSL (35.05 ft stage) • Poseyville Landfill • RGIS • #6 Brine Pond • Inundation • Power losses 15 Poseyville Landfill 16 17 #6 Brine Pond • Dikes overtopped by flood waters • Water sampled at time of flood • Dioxins/furans • >120 other analytes • Water lost to river had some chloride, but nothing else detected • Sediments do not appear to have been mobilized Bridge photo by Kelly House https://www.bridgemi.com/michigan-environment-watch/see-dow-chemical-ponds-dioxin-cleanup-site- after-michigan-flooding 18 Ongoing Evaluation of Flood Impacted WMUs • Dow believes that overall impacts to the river system from impacted WMUs were minimal. EGLE continues to evaluate. • Site improvements over time helped mitigate overall flood impacts at the facility. • On-site stormwater management systems (green space, curbing, detention basins) many of which were implemented following the 1986 flood were effective. • Inundation and regression mapping at impacted WMUs are being evaluated and sampling is being conducted to assess volume, and fate and transport of materials lost to the river system. • EGLE and others continue to assess other non-Dow flood impacts from household wastes, septic systems, debris, etc. 19 Tittabawassee River, Saginaw River & Bay Site • 2010 three party AOC • Phased investigations of site • Site includes: • 24 miles of the lower Tittabawassee River • The 22-mile Saginaw River • Portions of Saginaw Bay • Dioxins/furans are the primary contaminants of concern • By-products • Released in early 1900s • Secondary sources remain in some sediment deposits and banks What’s been done? • Construction every year since 2007 • As of 2019 • ~ 290,000 CY soil and sediment removed and disposed • 18 sediment deposits addressed • ~ 7.3 acres of sediment capped • 33 river bank areas remediated • ~ 4.3 miles of river bank stabilized • ~ 100 floodplain areas remediated 21 Site Progress as of 2019 22 Key Post-Flood Questions • Are the remedies intact? • Is there significant new contamination? 23 Stream Gages Maximum Predicted Shear Stress vs. River Flow Rate RIVER OVERTOPS RIVER OVERTOPS • Maximum velocity and BANKS BANKS shear stresses on river bottom and banks peak when river breaches the banks. • Shear stresses were determined using hydrodynamic model. (Reach D, LimnoTech 2009) 25 Maximum Predicted Shear Stress vs. River Flow Rate 26 Maximum Predicted Shear Stress vs. River Flow Rate 27 Maximum Predicted Shear Stress vs. River Flow Rate 28 Maximum Predicted Shear Stress vs. River Flow Rate 29 Maximum Predicted Shear Stress vs. River Flow Rate 2020 1986 2017 8 year flood event 30 Tittabawassee River Post-Flood Monitoring • The Tittabawassee River floods most years • Design of the remedies intended to protect physical integrity, including consideration of hydrodynamic flows • Monitoring plans are followed after floods, once conditions are safe • Key post-flood questions • Are the remedies intact? • Is there significant new contamination? • Maintenance will be conducted, if needed 31 Short-term Post-flood Project Activities • Inspection of integrity of remedies • Stabilized riverbanks (BMAs) • Preliminary and detailed evaluations complete – started early June • Includes naturally stable banks with higher TEQ • No significant impacts, some typical minor maintenance needed • Sediment caps (SMAs) • Evaluations complete – started mid-June • Caps performed as designed – upstream edge of one CCS seemed to be caught by debris • No evidence of contaminant releases from SMAs or BMAs • These results are similar to other floods • After the 2017 flood, inspections indicated that the caps and bank stabilizations remained intact, there was only minor damage 32 Short-term Post-flood Project Activities (cont.) • Solids cleanup at public parks, boat launches, Riverside – completed late May/ early June • Sampling at select floodplain locations • Remediated properties for recontamination • Expected to start this week • Newly deposited sediments for trend monitoring • EGLE and Dow samples taken for dioxins • In 2020 EGLE also looked at other contaminants 33 Homes along the TR – May 2020 Photo credit: Dave Sommers, CAG member 34 Post-Flood Recontamination Sampling • This monitoring helps evaluate whether additional sampling and/or cleanup needs to be considered • Monitoring at Riverside and West Michigan Park through 2018 • Riverside • Constructed 2008; 7 sampling events 2009 thru 2018 • Average 29 – 142 ppt (2018 was 45 ppt) • West Michigan Park • Constructed 2009; 10 sampling events 2011 thru 2018 • Average less than 5 – 133 ppt (2018 was 59 ppt) • 2019 ICS sampling of 7 remediated properties • 17 – 67 ppt 35 Newly Deposited Sediment Sampling Locations EGLE has sampled at Curry Park: boat launch some locations for more than 10 years Caldwell Boat Launch: boat launch, parking & levee Freeland Festival Park: deck Zilwaukee Imerman Park: levee, rink & boat launch West Michigan Park: levee Wickes Park: boat launch Riverside Drive: berm turfmat, berm levee 36 2020 Newly Deposited Sediment • EGLE took 11 samples from 8 locations, Dow took 4 samples from 2 locations • 2020 dioxin/furan levels in ppt TEQ: >1, 2, 4, 4, 10, 30, 44, 81, 108, 150, 150, 350, 419, 450, 1700 ppt; average = 234 ppt • EPA’s cleanup numbers are 250 ppt for maintained residential properties and 2,000 ppt for other land uses • However, these data are not for cleanup decisions, but for trends • The 2020 data appear to be within or lower than typical previous ranges, but additional assessment is underway • There can be “nuggets” that influence results • EGLE tested for other contaminants – metals, semi-volatile organics, pesticides and PCBs • These results came back as non-detectable or below applicable criterion 37 Long-term Monitoring • Routine monitoring and maintenance of remedies • The integrity of remedies and contaminant distribution is evaluated both routinely and after big floods • Monitoring dioxin levels in river sediment • 84 TR and 18 USR quarter–mile areas sampled once or twice a year • Overall surface weighted average concentration (SWAC) trends • Fish tissue concentrations and trends • The Agencies believe that trend monitoring over time will be the best indicator of cleanup progress 38 AOC Monitoring • DNAPL Recovery SMA 2-1 (Every 8-10 weeks) • Area(s) of Concern Monitoring • In-Channel Cap Monitoring – routine • Stable sediment deposits to assess ongoing stability • Elevation Surveys • Post-flood remedy inspection activities • Point-Based Surveys • In-Channel Cap Monitoring • Bathymetric Surveys • Bank Monitoring – BMAs and HSTs • Visual Inspections • Post-flood floodplain activities • Contingency chemical monitoring • Clean out of newly deposited solids in some areas • Bank Monitoring – routine • Chemical sampling of deposited solids • BMA Monitoring (Scoring System) • Post-cleanup floodplain properties • Undercutting • Inspect yard conditions for maintenance • Vegetation Cover • Canopy Cover • Recontamination sampling • Invasive