Obviously you shouldn't build a dam out of pure clay. That's why pure clay cores are inside the dam, to keep the core moist, and if your dam soil has a high clay content the dam needs to be dressed with top dirt to keep it from drying out. Think about what is going on underneath the dam if you don't remove the top dirt from the base. The water permeates the base of the dam until it reaches the core, that means the front half of the dam is 'floating' on water soaked soil. If that isn't the case then you don't need a core in the first place. h2o did the right thing in removing the top dirt, but the wrong thing in using pure clay for the dam. Not only should the dam be dressed with top dirt but also the sides of the basin down to at least the lowest water mark anticipated in future droughts. Otherwise you will develop leaks as the clay in the banks dries out and have a pond that slowly receeds over the years. Brettski, just do the math on the dozer. My D5 weighs about 26,000 lbs but has about 3200 square inches of 'foot'. It's not a matter of opinion, it's a matter of fact. It won't exert any more pressure than me walking on the dirt. Dozers make quite a fuss and mess driving over raw dirt with the grouser bars stirring things up but they are intended not to pack by design. If you packed that trench with a dozer and then built a brick wall on it it would crack all to pieces. I'll quit beating this horse.