SCS can definitely help, but I just realized they had a name change to Natural Resource Conservation Service. A lot of the soil maps are on the web now. Check this out.
http://soils.usda.gov/
The quick-and-dirty soil test is to roll of ball of in between your hands and then drop it on the ground. If the ball does not fall apart, there is probably enough clay to build a pond.
If your only water source is from the tap [mains], you may have a problem. Normal seepage could cost you a fortune.
Some of the best ponds are lined ponds which have an overlay of sand or loam on the bottom. You get the best of both worlds - robust benthic community and no seepage.
See info above about stocking levels. If you are going to overload the pond, it will not work.
-steve