I believe you can get the majority of the water out with a siphon setup. I drained the majority of two ponds - largest about 1.7 acres - with a 2" PVC siphon setup. The smaller 0.4 acres pond I ran it up and over the dam. The larger pond I ran the 2" PVC siphon down the 8" primary spillway pipe in order to avoid the extra dam height.

Note I said majority of the water. At some point the siphon will quit on you and it will be difficult to get restarted. At that point a pump is needed to get additional water out. Build a "trail" on top of the muck with pallets to walk the pump intake to the water. Slip off the pallet and you will be in trouble assuming the muck is several feet deep.

Nice thing about the siphon is it will run 24/7 until it sucks air in.
Have you already talked with a contractor on getting the muck moved?

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