Question

The DTB of a two inch sampling well is 100 feet. The DTW is measured to be 40 feet. What volume of water in gallons must be removed to initiate collecting water samples from this well?

Answer 1

I assume DTB is depth to the bottom of the well, and DTW is depth to the water line
I am guessing they want to know the volume of water in the pipe.

you have a cylinder of height 60 ft (100-40)
its base has radius 1 inch or 1/12 of a ft
area of the base is pi*r^2
volume of a cylinder is area of base * height
change cubic feet of water to gallons (use google)