Thanks for the advice FishinRod.

The NRCS was not involved, however I took all of the design guidelines from resources available on this site.

We have plenty of clay on site. In our region, it is almost all red Georgia clay.

The only rocks we have to worry about is hitting a granite vein. We are in a hotbed for granite, but most of it is in the higher elevations. I did not hit any in the 3' cores that i took. There is no sand in our area.

We will be above the groundwater table. The ditch feeding only flows when it rains and groundwater seepage areas are higher on the hill and below the dam.