So, I have great news. I think I have fixed my pond.
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The last few days were warm so, I went down to the pond to check it out. The bottom drain was still intact in the bank of the pond. I climbed down in the pond on the ice, and looked in the top of the drain. That section is about 6 feet long. The ice had raised it out of the fitting. When the pond drained, the ice and bank collapsed against the drain, pushing the top towards the pond. Since this happened, we have had several nights -20 F so, the bank was froze. I couldn't remove the pipe. I ran extension cords to the pond and brought the 80,000 BTU space heater out on the ice. This melted a lot of the ice around the bank.
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I got a heavy 6 foot bar, with a wide, thin end. I chopped at the frozen dirt and rocks for hours, and was able to remove the pipe. There was a 45? degree elbow where the pipe fit on. This was about 2 1/2 feet down and 2 1/2 feet in diameter. Rocks had fallen down inside. I placed a large, flat rock over the drain, as I had to chop the bank out six inches wider, so the pipe would fit on the elbow straight.
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After a few more hours of chopping I removed all the fallen pieces, then removed the rock I set on top of the drain. I laid down in the mud, with my head inside the hole, and removed most all of the rocks inside. The rubber seal looked good, so I rinsed it off, and placed the drain pipe back on. At first I couldn't get a tight seal, as I heard a small amount of water leaking. After turning it, and placing it in again, the seal was tight.
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I grabbed some 5 gallon pails, and started scraping up some 1 1/4 inch limestone from under the eves. That was the only area exposed. I ended up filling in the entire hole around the drain, up to where it was before. (probably 700 lbs of stone) I'm going to pick up a few hundred more pounds to place a little more around it. I will also try to melt/break more ice, so it doesn't collapse and hit the drain.
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I'm feeling real good about this fix. Also, no dollars were removed from my wallet. My back on the other hand.....