Dan,
Maybe they need a new pickup. I do and if could get that much to fix a couple of dams I could get one.
How your guy wants to do it is basically what i did. I dug out the old riser and several feet of pipe with a couple swipes with the big excavator. Put a coffer dam there to hold back the water. Dug out the rest of the pipe. Filled and packed dirt in up to where we wanted water level. Then installed pvc pipe inlet to the side of where the old pipe was at on existing fill. This pvc was 18 or 24 inches, can't recall, heavy stuff with gasketted joints. Used the 6' by 6' rubber anti seeps that you cut a hole in and run the pipe through the center of. Cut the hole tight and it leaves a rubber lip all the way around the pipe to clamp tightly with a couple of long hose clamps.
