Believe I'm no pro but had a similar problem on a deep well pump after a lightning strike that went down the casing.
Anyway the well man said the pump causes a whirlpool effect stirring up the sand and then it sucks it in. To keep from digging a new well he pulled it up 20' still way below the water level and that helped but not enough so I had to have a new well drilled (375'). My faucets were clogging with sand and also the back of the toilets it was so bad. I had to have the pressure tank cleaned out too all the lines flushed.
So you can try just raising the foot up higher, clamp it off and then trying it for a few days...If you don't run out of water and the sand problem is fixed then cut and shorten the pipe permanently.
Otherwise it souds like you need a new well which isn't very expensive for your depth.
Maybe a real "pro" will answer you though.