Neutralize with sodium carbonate and pour down the drain with at least 50 times the volume of additional water.

Is that baking soda? how much BS for my 1/3 gallon?

I have a septic, I would rather not pour down the drain. Can I pour it in the woods? street?

"sodium carbonate"

sodium bicarbonate (AKA 'baking soda')is a lot easier to find.

Unless you have a way to check pH (or know exactly what is in the solution) there is no real way to tell.

Add baking soda till there is a very little on the bottom of the container that does not dissolve.

Check in with your local landfill. Ours has hazardous waste materials drop offs such as paints, cleaners, solvents,etc the first saturday of each month.

You will have to use a lot more bicarbonate, but it will work. Add it gradually at first and do it outdoors. It will fizz at first. You can do what brickeye says and add until it does not dissolve. If you have some pool pH strips they will work. You can check the pH with red cabbage. It will be red-orange at acidic pH and blue if neutral.

Washing soda is sodium carbonate so if you have a bit of that around, you can use it. It is available in some grocery markets, better hardware stores, and where swimming pool supplies are sold.

You could use lime too.
Who's woods? You would have to check with your local officials about disposal in the street.

I have some important things to point out. Efflorescence on a basement wall is an indication of excessive water behind the wall. Have you fixed the problem that will eventually cause the wall to fail?. Removing it is treating a harmless symptom.

What is your procedure for neutralizing the sulfamic acid applied to the wall and running onto the floor? If you don't do it properly, you can cause faster deterioration of the walls.

How are you disposing of the material left over after your procedure? That is essentially the same problem as disposing of the 1/3 of the gallon you have left after your project.

1/3 of a gallon of stuff is probably not enough to wring your hands over.

Thanks for the added info.

My woods. I probably have a large yard debris pile somewhere that will never be disassembled. Actually, I probably have several!

The 5" sewer pipe that exits the wall (2' above the floor level) does sometimes get a little seepage during extreme spring rains (no gutters -- by choice). A mason put hydraulic cement around the pipe many years ago and it was fine, but the past few years it seems to have opened up ever so slightly and seeps occasionally. A new mason suggested 100% silicon caulk around it. So I did that and thought it would be a good time to clean up the efflorescence too.

I don't think too much solution got on the floor. I used a sponge to wipe the walls. Rinsed with clear water with a sponge also. It was such a limited area, the amount of solution involved was probably very little.