Chromium Release in Huron River Update

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​​​​ 919 Sunset Road, Ann Arbor, MI 48103

8 a.m.-5 p.m.
(excluding holidays)

24/7 water emergency line



Molly Maciejewski,
Water Treatment Services Manager


​​​​​​​​​​​​​​​​​​​​​​​treatment_plants_2022.jpg​​​​​​​​​​​Quick Links:

Frequently Asked Questio​ns

1. What happe​​​ned?

​​​​Michigan Department of Environment, Great Lakes, and Energy (EGLE) was notified at 3:21 p.m. August 1, 2022 by Tribar that it had released several thousand gallons of a liquid containing 5% hexavalent chromium into the sewer system. The company says it discovered the release on August 1 but indicated it may have started as early as the morning of July 30 according to Wixom city officials. 

EGLE tested the Huron River and of more than 145 water samples collected throughout 42 river miles since the release, three came back with detections of hexavalent chromium – two detections in Milford's Hubbell Pond and one in the middle of Kent Lake. The Kent Lake detection, completed by lab analysis – was 5 parts per billion (ppb) – just at the detectable limit of 5 ppb. The two Hubbell Pond detections were 11 and 9 parts per billion. All three were at or below values to protect aquatic life.  

View EGLE's Surface Water Sampling Results Map

After investigation and sampling, the bulk of the chromium that was thought to be released was found in Tribar's granular activated carbon (GAC) treatment system as trivalent chromium. Some chromium was also found in the solids at Wixom's Wastewater Treatment Plant. EGLE revised their estimate of the amount of chromium released to the river to be less than 20 pounds.  

​​​2. What is ch​​romium?

Hexavalent chromium, or Chromium VI, is a carcinogen if inhaled and can result in an increased risk of lung cancer. Total chromium is regulated by the Safe Drinking Water Act and has a Maximum Contaminant Level in drinking water of 0.1 milligrams per liter (mg/l) or 100 parts per billion (ppb)​.​

3. What about Ann Arbor's drin​​​king water?

The city's water remains safe for all uses. Safety is our number one priority.

EGLE continued to collect and analyze samples from specific locations along the Huron River between the confluence of Norton Creek, the source of the release, and Barton Pond through September 8.  The estimated travel time for water to move from Wixom to Ann Arbor was estimated to be on the order of one month. City of Ann Arbor continued sampling our intake in Barton Pond until mid October, more than two months after the release. Elevated chromium levels were not observed.  

4. What did the city do to protect drinking water? ​

City staff did the following:  

  1. Sampled our intake in Barton Pond.  Daily test results are posted at the top of this webpage. 

  2. Evaluated treatment modifications to our treatment process to remove any chromium found in our water supply to safe levels that meet all Safe Drinking Water Act regulatory requirements. We proved through bench testing that we could add a chemical to our treatment process to remove more than 90% of the total chromium in the water. We also have the ability to optimize the use of our groundwater supply as source water for the water treatment plant which is not impacted by the Chromium release.  ​

​5. What agencies were involved in response efforts? 

The Michigan departments of Health and Human Services (MDHHS) and Environment, Great Lakes, and Energy (EGLE), and local health and government officials worked together in Monroe, Oakland, Livingston, Wayne and Washtenaw counties to address the situation.  

6. What is the​​ impact?

The city's water remains safe for all uses. Safety is our number one priority.

Currently, there are no recreational limitations in the Huron River for canoe liveries or recreation. On August 12,  MDHHS lifted its recommendation for no contact with Huron River water after reviewing data related to Tribar toxic chemical release

Residents with questions about hexavalent chromium, potential health effects or exposures can call the MI Toxic Hotline at 800.648.6942, 8 a.m.-5 p.m., Monday-Friday. ​​ ​

7. How did the city keep the public ​informed?

In order to keep our community informed, the city posted all information, agency news releases and analytical test data related to this release on this webpage and promoted updates via city communication channels. You can subscribe to water-related email updates from the city to stay informed about future water news

8. Is it possible to clean up or stop the flow of chromium before it could reach Ann Arbor? 

The granular activated carbon (GAC) treatment units at Tribar and the Wixom Wastewater Treatment Plant captured the majority of the release.  ​

9. If chromium was detected in the Ann Arbor water supply, what action would the city take? 

We proved through bench testing that we could add a chemical to our treatment process to remove more than 90% of the total chromium in the water. We also have the ability to optimize the use of our groundwater supply as source water for the water treatment plant.

10. Is it possible to remove Chromium with filtration, and if so, are filters installed in the city water treatment facility? 

Filtration is not the process that would remove chromium. Metal precipitation and settling would be the most effective treatment.​

11. Is there an alternative source of water identified that can be used instead of the Huron River? ​

The city has two water sources, the Huron River and wells at Steere Farm. The Steere Farm wells are not impacted by this event and can be used if the Huron River source were to be compromised.​

12. Should residents be stockpiling water?

No. The city's water is safe for all purposes.​  

13. Does the water treatment plant observe a standard of 100 parts per billion (ppb) of overall chromium? 

Hexavalent chromium is not currently regulated at the state or federal level. The drinking water standard for total chromium is 100 ppb.

14. What was your sampling strategy for the Barton intake? 

Staff collected samples daily at our intake in Barton Pond. Sample test results are posted at the top of this webpage. 

15. What were the range of possible scenarios from best to worst case regarding this release in the Huron River? 

The best-case scenario was that the chromium released never reached the city's intake in Barton Pond at detectable levels. The detection levels for total chromium and hexavalent chromium are below health-based criteria, so non-detects would be protective of public health. We observed only one detection of total chromium, at a level of 1.3 ppb, which is just barely above the reporting limit of 1 ppb and is much lower than health-based criteria.   

The worst-case scenario was the chromium released reached the city's intake at concentrations above the Safe Drinking Water Act maximum contaminant limit of 100 ppb. This scenario would have required treatment. If it was determined that the city was not able to treat the surface water and meet Federal health-based regulatory limits, then we would have relied​ on our well water sources until the plume passed the intake.

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