Soil type and pond size are the two main factors in determining the amount of Sodium Bentoite required to seal a pond. Normally a coarse or pores soil will require a greater amount of bentoite to be applied.
This chart estimates ponds per square foot of area to be sealed
PRIMARY SOIL TYPE
||1.0 to 1.5 lbs per sqf
|SANDY SILT 20% CLAY MIN
||2.0 to 2.5 lbs per sqf
||3.0 to 3.5 lbs per sqf
||4.0 to 4.5 lbs per sqf
|ROCK OR GRAVEL
||5.0 to 6.0 lbs per sqf
If pond size and soil type is known, the chart above gives a good estimate on the amount of Bentonite needed to seal a pond. The chart is based on water depths up to eight (8) feet.
For depths greater than eight (8) feet:
Since greater water depths increase the downward pressure on the bottom depths of the pond. It is recommended increasing the application of Bentonite by one pound per square foot, for each additional eight (8) foot of depth.
There are three basic application methods:
The Blanket Method
The blanket method is usually the most effective method for sealing a lake or pond with bentonite. The first step is to prepare the surface to be treated. Remove all large rock, trash and vegetation, including any trees and roots. Roots left in the ground will decay over time, leaving potential for future leakage problems. Next remove 4” to 6” of soil from the bottom area of the pond (set aside). Fill in any deep holes or crevices with a mixture of one part bentonite to five parts soil. Then pack and smooth that area.
Cover prepared area with prescribed amount of sodium bentonite. It is very important that the bentonite layer is evenly placed and that there are no bare or thin spots. 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 return soil, take care not to disturb the bentonite layer. Finally, compact the treated area by rolling or tamping. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil and bentonite layer. It may take several days for the bentonite to reach the point of saturation and fill the voids in the underlying soil.
Mixed Blanket Method
Begin by preparing the surface area to be sealed, follow the same preparation suggestions as described in (The Blanket Method). If the soil is too dry, lightly moisten it. Then disc or till the bottom area of the pond 4” to 8” deep, then roll or drag the surface untill it is smooth. This initial plowing and blending will assure consistency of the soil throughout the bottom of the pond before the bentonite is applied. Next apply recommended amount of bentonite (refer to our recommended amount chart).
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 to 4” to 8” of soil by disking, tilling or raking. It is very important for the bentonite to be mixed uniformly with the soil. To ensure that there are no bare or thin spots, we recommend multiple passes over the area to be sealed.
Finally, compact the treated area by rolling or tamping of the soil. Use care when filling the pond. A gentle water flow is recommended to prevent erosion of the soil/bentonite layer. It may take several days for the bentonite to reach the full saturation and fill any voids in the soil.
The Sprinkle Method
The sprinkle method is recommended only when it is not feasible to drain the existing pond. Our in case of isolated leaks when a spot treatment may be a possible alternative. This method is less effective than the other two methods for several reasons. Uniformed placement of the bentonite is difficult. The pond may have debris such as trash, vegetation, logs, large rock, etc, which may prevent sufficient coverage. If the pond bottom can be cleared, this method has a greater chance of providing a good seal.
A granular grade of bentonite is best suited for this method. 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 in the area you want to treat. The granular bentonite will sink to the bottom of the pond or be drawn into porous areas where they will swell and reduce the seepage rate.