Testing materials to seal a pond or lake
We are often asked how to evaluate soils used to seal ponds and lakes; our approach is two tiered. The first thing we do is a very simple test, then if we need further research, we bring in a soils scientist or engineer to utilize techniques that improve the quality of marginal materials. We will outline the simple method here.
To quickly identify the best clay material, grasp a handful of moist earth in your hands and roll it into a ball shape. If the ball maintains its form when you drop it on the ground, it may contain sufficient clay. Take the ball and roll it between your hands to form a thin pencil shape. If this pencil shape of clay will bend before breaking, the clay is likely of sufficient quality to seal a pond. There are always exceptions, so move onto the next test.
Using something like a five-gallon bucket, drill several holes along the vertical edge near the bottom of the bucket. Holes of around 3/8th inch work well. Next, fill the bottom of the bucket with four inches of crushed gravel, such as 3/4-minus. On top of the gravel, place about six inches of what ever soil/clay type material you plan to use for the pond. Thoroughly compact this clay layer throughout the bucket, paying particular attention to the edge. Make sure the clay is somewhat moist. Moist enough to make a ball out of the material is about optimum. Now fill the bucket to the rim with water. Cover the bucket with an impervious surface such as plastic. Wait a couple days, then refill the bucket. The soil needs time to saturate with water. Cover the bucket once again. Now wait up to a week to see if the soil will hold water. Obviously you can check after the first day to see if the material failed. Our experience has been that if you lose less than an inch of water after a week in the bucket, you have good material. We don't seem to get as good of compaction in a bucket as we do out in the lakes and ponds themselves. This is why we relax our expectations within the bucket.