When my .15 acre farm pond was renovated last summer there was about 4' a muck in the bottom that was excavated and most was buried under about a foot of topsoil. Some of it must have been buried very well though and now I have 2 areas that were always wet before the dirt work that has "oily" water is coming up and it smells similar to the barnyard. Don't mind the smell but all the grass and clover has died out in these areas. Other wet areas are doing just fine.
I assume this is the muck coming up through the soil. Are there any soil additives that I can apply to speed the decomposition of this muck?
Your assumptions are all correct. The "oily water" is mostly likely algae from the buried sludge. It could also be a bacteria that is attacking iron in the water that saturated the sludge and rose to the surface.
Maybe if Bill Cody sees this, he will provide more information. He is the real expert.
Pond muck shouldn't be spread in a deep layer, unless it can be regularly "turned." It is the same as creating garden compost from grass clippings and leaves. It needs oxygen to decompose.
More than likely, the muck taken from your pond was anaerobic. That is, there was a near total absence of oxygen at the bottom of your pond to help break down the organic materials like leaves, dead plants, dead fish, fish poop, etc.) that collected over the years. That muck produces some nasty smelling gases and some of the oily slick you are seeing.
What you experienced is extremely common. Ponds have thermal layers based on the weight of the water vs. temperature. Typically, the lower layers of a pond have the cooler water, which is usually the heavier water. Depending on the surface area, and the depth, this water becomes devoid of oxygen. That is where the dead fish, the fish poop, and the leaves congregate.
Spreading the muck in the sun and air is usually far better than burying the muck several inches below the ground where it gets little oxygen. It is how today's fossil fuels of coal, oil and gas formed millions of years ago.
Even above the soil, spreading it several inches deep will tend to let the sun and wind seal it at the exposed surfaces. That prevents oxygen from penetrating below that crispy cover.
It needs oxygen to decompose into what we think of as good organic compost. Burying it, or spreading it thickly over otherwise good topsoil, keeps it from decomposing to the conditions we would prefer to have on our properties.
In your case, is the area too wet to plow, disc or roto-till? Doing so would help bring it to the surface where it would mix with other soil filled with good bacteria and critters like earthworms. It will get a lot more oxygen. The bacteria and earthworms will start to work on it pretty quickly.
Good luck,
Ken