The Natural Resources Conservation Service staff often gets asked: “I have a pond that is leaking. How do I fix it?”

It is common for new ponds to leak. Most new ponds will quit leaking once the soil in the reservoir area has had a chance to settle and become saturated. Also, the process of filling with water the first time will deposit some silt and sediment in the reservoir area. These silts and sediment are very effective at sealing a new pond.

One of the first steps in new pond dam construction is the installation of the core or cut-off trench. This is important in preventing water from seeping under the dam. A core trench is simply a trench that is cut along the centerline of a new dam. This trench needs to extend, in depth, to an impervious material. An impervious material is any material that water cannot seep through. This material could be rock, shale or even heavy clay. After this material is reached, the trench should be filled and compacted with the heaviest clay available.

Many older ponds were built without having the core trench installed. This is the cause of most of our older ponds leaking. To correct this problem, it is usually necessary to bring in a track hoe or backhoe with an extendable boom to cut a new core trench. Generally a traditional backhoe cannot reach deep enough to cut a core trench through the existing dam and the soil under the dam to an impervious material.

The new core trench should be cut into the front, or reservoir, side of the dam. It should extend to an impervious material as was described above. This is just like the installation of a core trench before building a new dam. The trench should be filled and compacted with the soil that was removed. The track hoe or backhoe should place a layer of soil no more than 8 to 10 inches in the trench and then compact it using the bucket. Due to the increased compaction of the soil in the trench, additional fill material will need to be used. Usually this can be obtained on the site by simply taking soil from the banks of the pond. This soil should be free of rocks, tree roots, limbs or any other vegetation. Heavy clays are the best materials to use. Silt or sediment from the pond should never be used in the core trench.

Another cause of ponds leaking is rock. Much of the rock underlying eastern Kansas is limestone with seams and cracks. When this rock is encountered, during the construction of a pond, a minimum of 12 inches of clay should be placed and compacted over the area of rock. Many times this will seal the rock ledge and keep it from leaking. If there is a lack of heavy clay on site, bentonite clay should be added at a rate of one pound per square foot.

Many times a pond will leak to a certain level and then will maintain that water elevation. This indicates the leak is at approximately the elevation that is maintained. Look for rock outcrops and treat them as described above. If no rock is observed and no obvious other problems are noted, the area about 5 feet above the waterline and about 5 feet below the waterline should be treated with bentonite clay. Again, the rate would be one pound per square foot. The area above the waterline should have the bentonite applied and then lightly incorporated into the top 1 to 2 inches of soil. The area below the waterline will need to have the bentonite simply poured through the water. The waterline around the entire pond should be treated.

If the pond goes completely dry, the leak is in the bottom of the reservoir area. The entire bottom should be treated with bentonite clay. If possible, the bentonite should be incorporated within the top 1 to 2 inches of soil. This will dramatically increase the chance of sealing the leak.

In the extreme cases where bentonite does not seal a pond, a rubberized liner can be placed in the pond. A liner is expensive and must be installed by professional crews. The cost of this option is approximately $12,000 per acre.

Sometimes burrowing animals such as beavers and muskrats will dig into a pond dam creating a leak. These animals should be removed or trapped. Kansas Department of Wildlife & Parks must be contacted before the animals are trapped or destroyed.

Bentonite clay is usually available at farm supply and feed stores within the area. Most stores carry it in 50-pound bags and charge between $5 and $7 per bag.

If you have questions concerning any conservation structures, call the Natural Resources Conservation Service office at 843-4260, ext. 3.

— Alan Gentry is a soil conservation technician for Natural Resources Conservation Service.