Rickro:

This is not an easy question to answer with do it yourself tests or even laboratory tests unless it is a no brainer with several feet of good clay. Dave is right about digging some test pits. As Ric indicates by the test method, what you are really looking for is permeability, which is related to the clay content, but also to other soil properties. Before using any test method, you will need to convince yourself that soils are relatively uniform in the area you are considering for the pond. It would only take a very small area of high permeability soil to drain a large amount of water. The best way to do this is with multiple borings or test pits.

After confirming soil types in the pond area, you have several test methods available. Ric's method will give some good qualitative information but I'll explain a few more options where a geologist or engineer could be helpful.

First, you could have lab particle size testing done, which will tell you the actual percentage of sand, silt, clay gravel, etc. (my company charges $85 each) be sure to order the "loss by wash" for the clay percentage. There is a simple calculation called Hazen's formula where you can take the particle size results and approximate the permeability.

You can also have a few laboratory permeability tests done on soil samples (more expensive $175-$300 each). These are recompacted soil tests and tend to give lower permeability results than actual soil conditions because the soil structure is not preserved. Estimates of permeabilty can be used to calculate the time it takes water to migrate through a soil.

The method I prefer is to conduct field testing on your soil using a double ring infiltrometer. This is really a fancy perc test. This involves setting two concentric rings into the soil which will form the base of your pond. The outer ring could be a drum cut in half and the inner ring a piece of 12-inch PVC. The basic idea is to fill both rings with water and measure the drop in the inner ring over time. The water level in the outer ring is maintained constant and insures that you are measuring vertical infiltration in the inner ring and not just horizontal leakage under the PVC.

Lastly, and probably the first thing to do is call your state agency and the NRCS office. They probably have pond suitability information based on soil type along with soil maps of your area. The maps are very general and you will still need some borings or pits to confirm, but depending on your soil this may be all you need to do.

This sounds like a lot of effort and it is, but if you have any questions about your soils holding water it's better to know before you sink money into constructing a pond that won't hold water.