Introduction
Leaking ponds can be a frustrating experience. Avoid problems by using proper construction techniques, including anti-seep collars on pipes when ponds are constructed. Many pond leaks also can be prevented by a program of pond maintenance that includes prevention of tree growth on dikes and removal of burrowing animals before they dig holes. When leaks do occur in ponds there are a variety of materials and management techniques that can be used to stop the flow of water.

Disking
In certain soil types large cracks appear when ponds are drained and dried. These cracks may cause previously well sealed ponds to leak. Before refilling the pond, disk the pond bottom. Disking fills cracks and mixes the soil into a smooth layer that can be compacted to form a new water tight seal in the pond. Additionally, disking helps bring possible aquatic disease causing organisms to the surface where exposure to sunlight can destroy them. Disking also aerates the pond soil, and oxidizes accumulated organic matter. Unoxidized organic matter can contribute to summer oxygen problems.

Clay
Ponds built in gravel beds or in rock shelves generally do not hold water very well. A clay lining at least 12 inches thick is needed to properly seal these ponds. Construction costs may exceed $5,000 per acre. Ponds built in rocky areas may require at least one foot of well-packed clay in the pond bottom and at least six inches of clay on interior slopes to prevent leaks. If less clay is used, the pond will usually develop leaks again within a few years; particularly if the pond is drained and dried occasionally as is necessary in fish culture. Ponds that are frequently drained are especially prone to leaks. As the pond bottom drys, large cracks appear that open channels for water drainage.

In areas where clay is available, it is usually the least expensive method of repairing leaking ponds.

Levee Repair
Leaks in pond dikes are best repaired from inside the pond. To do this, drain the pond down one to two feet below the site of the leak. Then using shovel or back hoe dig out the area surrounding the leak for several feet back into the dike. The resulting trench is filled with clay and compacted every 8-10 inches as it is filled.

Barite
When it is not practical to drain the pond below the level of the leak, seepage sometimes can be stopped by pouring barite, a clay substance similar to bentonite but about twice as heavy, into the water over the area suspected of leaking. The barite forms a gel-like barrier that works like an automotive radiator sealant to plug leaking soils.

Barite costs $ 4.50 per 100 pound bag. For small leaks in dikes, 500-1,000 pounds of the substance poured over the seeping area should stop the leak. Barite will not seal holes caused by the digging activities of muskrats or beavers.

Bentonite
Sodium bentonite or "drillers mud" has often been used to seal leaking ponds. When moistened, bentonite swells eleven to fifteen times its original size, plugging the spaces between soil particles as it expands. Because of cost, bentonite is best used in spot applications on small leaks. It is applied at a rate of one to three pounds/square foot. The actual amount depends on soil type and severity of the problem. Usually, if a pond is leaking badly enough to require bentonite, the higher application rate is required. Bentonite is supplied in 100 pound bags. In a drained pond bentonite can be spread by hand or with a garden or tractor sized lime spreader. A disk or rototiller is used to work the bentonite into the pond bottom.

Alternately, bentonite can be applied in a blanket layer. A layer of soil four to six inches deep is removed from the pond bottom. The bottom is smoothed with a roller. Next, a layer of bentonite is applied to the pond bottom at a rate of 1-2 lb/sq.ft. To complete the procedure, pond bottom soil is spread back on top of the bentonite and compacted. It is important to have a layer of soil sufficiently deep over the bentonite to prevent animals and livestock from puncturing the seal created by the material; four to six inches is usually adequate.

Do not attempt to apply bentonite on a windy day. It is a fine powdery substance and is easily blown away. Bentonite costs $3.80 per 100 pound bag. At the recommended application rates bentonite costs $1,655 to $4,966 per acre of treated pond bottom.

Concrete, Fiberglass and Cement
Concrete or fiberglass liners are not cost effective in most situations, although concrete can be used to fill holes in rock strata, effectively reducing some problem leaks. Dry portland cement also has been used successfully. It is mixed into the soil or poured through the water like bentonite or barite. Application rates are also the same, one to three pounds/square foot. The cost is slightly higher than bentonite or barite, $4.85 per 100 pound bag.

Plastic Liners
A plastic, vinyl or butyl rubber liner may be the only successful solution for some badly leaking ponds. Before a lining can be applied, the pond bottom must be smoothed and all sharp rocks and stumps removed. It is often necessary to line the pond with six to eight inches of sand or screened soil before the plastic liner is put into place. The minimum thickness for a plastic liner is eight mils. The liner thickness should be increased to 15-30 mils if gravel is present in the pond bottom. A ten mil PVC liner costs about $0.25 per square foot or $10,890 per acre. Plastic liners are sold by weight. A 20 mil liner costs twice as much as a 10 mil liner or about $0.50 per foot. Liners made from material other than PVC may be priced differently.

Many grasses can penetrate plastic liners. It may be necessary to sterilize the soil under the liner before it is installed. A minimum of six inches of earth must be placed 3 -4 feet over the edge of the liner after installation to protect it from punctures.

Pond liners will not work in all situations. Water pressure under the liner can force it completely away from the pond bottom. This problem can occur in areas where water tables rise near the surface or if springs are located in the pond.

Muskrats, other burrowing animals, deer and livestock may tear plastic liners. Consequently, they may need occasional repair or replacement. One place to find bentonite, barite, plastic liners or other pond sealing materials are oil field equipment companies. Some companies specialize in containing oil field spillage, usually salt water, and can knowledgeably help you select the right materials for your specific application. Many companies also specialize in aquaculture and water treatment applications.

Gley
Gley is another material useful for sealing ponds. Gley is produced by spreading a six to nine inch layer of very fresh, green manure over the area to be sealed. The manure is then covered with plastic, cardboard, or anything else that prevents oxygen from reaching the manure so that it will ferment anaerobically. The fermentation produces a bacterial slime in one to two weeks that can permanently seal soils. After two weeks the plastic or other covering can be removed and the pond can be filled with water.

Livestock
Livestock such as hogs or cattle penned into a pond will seal the soil in a way similar to the gley method. Livestock provide the added benefit of hoof action to help mix and pack manure into the pond bottom. The livestock are left in the pond until the bottom has been completely covered with manure and well trampled. Occasionally watering the pond bottom will speed this process.

The gley or livestock method of sealing ponds may be the least expensive when materials or animals are readily available.

Resinous Polymers
The need to contain toxic wastes has spurred research into new methods of sealing landfills and lagoons containing various types of waste products. Some of these new methods have application for the pond owner.

Resinous polymers and emulsifiers are mixed in an EPA approved non-petroleum oil based carrier. This material is best mixed with the soil and compacted into the pond bottom. Soil and polymer are mixed in six inch increments. Usually this lining is at least 12 inches deep. Wetting agents are often used to improve soil compaction during construction of the soil/polymer lining. Cost is $10 to $12 per gallon and about 450 gallons are needed per acre for a total cost per acre of about $5,000. This estimate does not reflect the cost of construction equipment necessary to mix, spread and compact the mixture. Success rates with this compound are 70% to 90%. Polymer resins may be poured directly into the water, however, it will kill fish when applied in this manner because the compound coats gills and suffocates fish.

It is almost always less expensive to build the pond in proper soil using the correct equipment than to repair leaks afterwards.

Leaks in fish culture ponds increase production expenses through increased pumping costs and labor. Small leaks are troublesome but not expensive to repair; however, major renovations can be quite expensive and rarely cost effective. Clay is the most common substance used to seal ponds, however, other materials and methods including drillers mud, polymers, and livestock have been used with success. The method chosen depends upon the nature and severity of the leak and cost of repair.