That is too close.
I love willows but will not plant one because we have a septic tank and leach fields.

My willows are on the opposite side of the house/garden from my septic (or any other water-related house utilities).

My septic is in 20-30 foot break between hickories, oaks, sweetgum, redbuds, and red maples. If I leave a pile of fallen leaves too long, I'll find a mass of tree roots come up into it. It's been working for 9 years - I don't think tree roots are as much of an issue as most people fear. Or I'm happily in denial (also very likely).

Curly willow does not have the invasive roots that a weeping willow or basket willow does. I would not be worried about it. What I would worry about near your septic field is our native red maples.

Nancy the nancedar

Keithnrjd,
Don't plant anything near your septic tank or leach fields.
Grass is nice.
And for God's sake, don't plant a Willow anything by your septic tank or leach fields.
Unless your rich and love problems.
Research willow on the internet.
Nuf said.

As a septic inspector I don't recommend any tree root zones anywhere near a septic drain field. I've seen roots from all manner of trees infiltrate the lines.

Thanks Nancy. I always thought that the curly's are less invasive,root-wise. I have a mature threesome (I braided) I took slips from a couple weeks ago and they are fully rooted and leafing out in the garage. We're not supposed to plant them (at least in the front yard) but I need them in the back yard.
If you plant curlys, try to site them with no trees behind them so you can appreciate their contorted shapes in winter against the sky backdrop.