Temporary layer of mud in well casing while flushing chlorine

[triksterMTL]

Good morning!

Here's my setup:
- Drilled well, 200 feet
- Submersible pump hung at 180 feet
- Metal casing from the top to 40 feet
- No sleeve after 40 feet
- Produce 4 GPM of water
- Static water is 8 feet

I shocked my well with chlorine for my annual disinfection, and then I flushed the chlorine from the well this way:

1) I run the water from the garden hose for 40 minutes (5 GPM).
2) I let the well recover for one hour.
3) I repeated this process for +/- 10 hours

During the middle of the day, I measured the level of water to make sure I don't empty the well, and I noticed a layer of mud at +/- 20 feet with my tape measure.

Few minutes later, and repeated the measuring process to notice that the layer of mud was at +/- 30 feet.

Finally, fee minutes later, I was able to measure up to the pump, 180 feet from the top, without any resistance.

My question is the following: What could cause this layer of mud in the metal casing ? Could it be the effect of using intensively the pump that makes the water percolate up to the top, bringing at the same time the silt present in the water when I shock the well ?

 

[Valveman]

Static water at 8' in metal casing, it is probably rust instead of mud.