In situations where I've seen muck sucked out of ponds the slurry of sludge water is pumped to an adjacent area (tree area or low land) and the water is allowed to soak away leaving a layer of organic nutrient rich sludge on top. Sludge is almost all organic, that biologically decomposes and would be very good for a garden or place you wanted plants to grow.
Yes, it is very rich. Can be too rich for much to grow for a couple years. I've got probably 100 ton stacked up now from cleaning my pond out last fall. It was about 4 feet thick in the pond. As someone else posted, unless you get it flattened out it will probably never dry completely.
