How To Seal a Leaking Pond
If your new pond leaks and you're having trouble finding out what is causing the problem, not to worry. There are a few things you can do to keep your new pond from leaking, as well as a few things you can do before you're ready to fill your new pond with water. I'm speaking mainly here about newly built farm ponds, not your typical small backyard garden pond that will usually have a pond liner to retain the water.
The major problem with a newly built farm pond is that they are built by inexperienced bulldozer operators that don't understand soil types. They may think that pushing the dirt to form a hole will hold water leaving you with your dream pond. This is not always the case. If you have a very sandy soil, you will have to usually have a high-clay soil shipped in on truck to cover the base of the pond to form a good seal. Otherwise, the water will puddle after a rain and then just recede into the soil within a short time. A good pond base needs a clay soil that will keep the water from receding. As mentioned above, you can either have a clay soil shipped in and spread over the pond base, or you can buy a product called bentonite spread over the pond surface. Bentonite is a cost-effective way to treat porous soils when building a new pond. Two commonly used variations of Bentonite for sealing ponds are calcium bentonite and sodium bentonite. Both are acceptable for sealing a leaking pond.
If you live on a farm and already raise cattle, pigs (swine), or even goats, you also have another, more frugal, way of dealing with a leaky pond. By simply fencing in your livestock around the pond and spreading their feed onto the pond surface you can build a durable pond base in hardly no time and without the expense of the options mentioned above. Adding organic matter such as manure, leaves, straw, grass, sawdust or hay will also help build the pond base. What happens here is that the animals' hooves trample the pond bottom, working in the organic matter, and basically seal the pond to retain water. As an alternative, Bentonite can also be spread over the pond surface without worry of contaminating the livestock. Their hooves will work the bentonite into the soil along with the organic matter and provide a perfect pond base that simply won't leak.