In February 2020, I purchased some land with a 0.2 acre pond and shortly after that, the dam started to fail.

There was a smaller pond at one time and then someone who didn't know what they were doing extended the dam to make a bigger pond. This is where the dam is failing.

I have the pond drained now, and I plan to rent a large track loader to start reworking it.

I have no experience with building/repairing dams and am looking for some advice.

My plan is to start digging out the inner portion of the dam and repacking/tracking the dirt in. Then reworking the outer portion of the dam. I'm hoping I don't have to remove the whole thing and start over.

As part of this repair, I'm planning to double the width of the top of the dam.

Here are some pictures of the dam failing and the manually drained pond.

Best of luck. I have no experience so no advice.

Look into how to core a dam. I am about to start this today on a mainly excavated pond that I just started digging. The first step is to push soil behind the dam until you get down to good clay. Then good clay is added in 6" lifts, each of which is compacted with a sheep's-foot roller. The core is designed to keep water inside the pond. For me, I will also trench and pack a 2' wide core with a backhoe, packing the trench with the bucket as I go. We did this on our last pond and it holds water like a drum, but I was able to tie into good grey clay and the rest of the dam was red clay. My other 2 ponds were cored with a dozer, but that takes considerably more time (and of course is better). In your case, the old section of the dam may be fine, so you might be lucky find that an excavator could be used to "trench-core" the new section tying into the old core in the old section. I first saw "core-trenching" done on a wetland we had constructed a number of years back. This mixes the soil and hopefully disrupts and permeable lenses in the original soil, but it requires the soil to be mostly clay so the mixed soil is impermeable to water under the pressure generated by the depth of the water (deeper layers are most vulnerable to leaking due to greater water pressure.