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Many ponds on a variety of soil types are prone to water loss by seepage. This water loss can be controlled by the application of western sodium bentonite clay. Sodium bentonite is a naturally occurring clay which contains no additives.
Sodium bentonite clay swells up to12 times its dry size when it becomes wet. Bentonite is environmentally safe and does not affect the water, livestock or wildlife. When properly applied it will not harm fish. Bentonite is easily applied. In the case of small ponds, it can be applied with simple hand tools and, for larger ponds, with ordinary farm equipment. Blanket method  The blanket method can be used in new pond construction and in existing ponds that can be drained. This is usually the most effective method to control water loss. However, more care is required during the application process.
The first step is to prepare the surface to be sealed. Remove all rocks, trash and vegetation, including trees and roots. Roots left in the ground will decay over time, leaving the potential for future leakage problems. Remove the top 4 to 6 inches of the soil from the pond bottom. Fill any deep holes or crevices with a uniform mixture of one part bentonite to five parts soil. Then smooth the area by roller or drag.
Cover the area with the prescribed amount of sodium bentonite. We recommend a fine grade of Cowboy Bentonite, "Pond Seal," for this application. It is very important that the bentonite layer is even and that there are no bare or thin spots. This will ensure complete coverage and a water tight seal. After the bentonite has been spread as evenly as possible, carefully replace the 4 to 6 inches of soil that was removed earlier. While spreading the soil, be certain not to disturb the bentonite layer, as this could leave bare spots which could allow water loss to continue. If livestock will have access to the pond, the cover coat must be thicker than 4 inches. In this case, a top layer of gravel would be best to protect against puncture by cattle hooves.
Finally, compact the pond bottom by rolling or tamping. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil and bentonite layers during this final phase. It may take several days for the bentonite to reach the point of full saturation and fill the voids in the underlying soil.
Mixed blanket method
 The mixed blanket method can also be used in new pond construction and in existing ponds that can be drained. It may be less effective than the blanket method due to uneven mixing, but increased amount of bentonite and/or thorough mixing can minimize this possibility.
Begin by preparing the surface to be sealed. Remove all rocks, trash and vegetation, including trees and roots. Roots left in the ground will decay over time, which leaves the potential for future leakage problems. If the soil is dry, lightly moisten it, then plow, disc or till the bottom of the pond 4 to 12 inches deep, then roll or drag the surface until it is smooth. This initial plowing and blending of the soil will assure consistency of the soil throughout the bottom of the pond before the bentonite is mixed into it. When this is complete, apply the prescribed amount of sodium bentonite.
The bentonite can be spread by several different methods, however, we recommend a fertilizer or seed spreader to ensure even spreading. Mix the bentonite with the top 4 to 12 inches of soil by discing, tilling or by hand raking. It is extremely important for the bentonite to be mixed uniformly with the soil. To ensure that no bare or thin spots will be left, we recommend multiple passes over the area. If livestock will have access to the pond, the cover coat must be thicker than 4 inches.
Finally, compact the pond bottom by rolling or tamping. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil/bentonite layer during this final phase. It may take several days for the bentonite to reach the point of full saturation and fill the voids in the soil.
Sprinkle method
The sprinkle method is recommended only when it is not feasible to drain the existing pond, or in cases of isolated leaks when spot treatment may be a possible alternative.
The sprinkle method is recommended only when it is not feasible to drain the existing pond or in cases of isolated leakes when a spot treatment may be a possible alternative. This method is less effective than the other methods mentioned above for several reasons: Uniform and accurate placement of the bentonite is difficult; The pond bottom may include debris such as trash, vegetation, logs, rocks, etc.,which may prevent sufficient coverage. If the bottom of the pond can be cleared, this method has greater chances of providing a good seal.
The granular grade of bentonite is best suited for this method of placement. The granular bentonite should be used when using the sprinkle method because the particles are large enough to sink to the bottom, while finer particles cloud the water and stay in suspension. Begin by simply sprinkling the prescribed amount of granular bentonite on the water surface and allow it to fall into place. The granular bentonite particles will sink to the bottom of the pond or be drawn into porous areas where they will swell and reduce the seepage rate.
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