Hello, and thank you for submitting your inquiry.

This is a tricky situation because of course roots in your system are a problem. Copper sulfate doesn't necessarily kill the tree or shrub completely. So if you kill and get rid of the roots without removing the trees/shrubs involved, you could potentially get regrowth of the roots and will still have this very damaging situation causing potential future damage to your septic system.

Have you already connected with Livingston County Environmental Health? If you haven't already, this would be the best source of localized information for your situation. Their full contact information (including some educational information as well) is located here: https://milivcounty.gov/environmental-health/septic/

The following information was provided by the Michigan Onsite Wastewater Program:

Tree/plant roots are a major concern and are one of the leading causes of system failures as reported by local health departments. 2017-2019 Statewide Failed Sewage System Evaluation Summary Report (michigan.gov) Unfortunately, there is not a lot that can be done regarding root clogging once the roots are already there, so prevention is the best, potentially only real strategy. It is recommended to have all plants with deep root systems a minimum of 5-10’ away, but some large and water-seeking species warrant farther isolation distances.

There are chemicals that are designed to kill roots in septic systems (copper sulfate), which will temporarily kill the roots, but it does not dissolve or otherwise remove the roots that are there so they must be manually removed. It’s also possible for the tree/plant to recover after a copper sulfate treatment and continue to grow new roots unless the tree/plant is removed. I can’t personally speak for the effectiveness of a copper sulfate treatment. If the roots are within the tank, there are likely structural issues as roots should not be able to enter a water-tight septic tank. If a system is full of roots and they are experiencing issues, the options end up being repair (replacing clogged pipes/stone) or a total replacement of the system.

The National Onsite Wastewater Recycling Association (NOWRA) does have some information about that in their homeowner training “user guide”. See page 23
Users Guide | National Onsite Wastewater Recycling Association (NOWRA)

Thank you. Appreciate it.

You are welcome. I hope you will be able to take care of this roots so you can prevent any major damage to your system.