Thank you for contacting the UVM Master Gardener Helpline with your question about controlling Japanese Knotweed. I’m sorry you are dealing with this invasive weed. It is unfortunate that the repeated flooding has led to many wide-spread invasions.

Since you mention a well, it sounds like you need to avoid a chemical solution. we have a number of articles that you will find helpful:

This article describes three recommended phases to controlling the weed without chemicals:  https://www.econewsvt.org/news/you-can-beat-knotweed-without-chemicalsheres-how

The Vermont Invasives site also has information about how to control the weed:   https://www.vtinvasives.org/invasive/knotweed-japanese

University of New Hampshire Extension published “When is the best time to control Japanese Knotweed?”: https://extension.unh.edu/blog/2018/09/when-best-time-control-japanese-knotweed

While controlling Japanese Knotweed is a multi-year project, if you are able to stay on top of it, you should be able to get it in control.   

We hope this information is helpful. If you have any additional questions, please feel free to reach out.