A pond that leaks is a real disappointment. The two most likely reasons are the pond was not built correct in the first place or some of the components such as a pipe has rusted out. Other times however unforeseen conditions can be the cause. The Natural Resources Conservation Service can do a site review of your pond to help determine what the possible reason for the problem. Please see some key elements of a properly build a pond dam.
Below are some methods for sealing a leaking pond. Sorry, but the best solution normally is to drain and re-build the pond in a more correct manner. A pond can be re-built more economically with better results. There is no guarantee that fix will work.
I. Site Preparation - REQUIRED FOR ALL METHODS A. Drain and dry area to be sealed B. Remove vegetation, stumps, debris, loose rock C. Cover all voids with soil D. Protect sealed area from puncture (livestock, etc.) E. All methods, except liners: 1. Spread in 6" - 8" lifts 2. Thoroughly mix 3. Compact at optimum moisture II. Methods A. Compaction 1. For well-graded soils only with > 10% fines for sealing 2. Scarify 8" - 10" depths or lifts 3. Compact (sheepsfoot usually) at optimum moisture 4. Increase for water depths > 10 ft. B. Coarse-Grained Soils (Inadequate Clay) 1. Earth blanket a. Soil should have approx. 20% clay by wt. b. Spread in 6" - 8" lifts, 1-2 ft. thick c. Compact at optimum moisture 2. Bentonite (DRILLER'S MUD) a. High shrink-swell sodium clay that swells 8-20 times original volume b. Not satisfactory for fluctuating water level (shrinks and cracks when dry) c. Thoroughly mix with soil in 6" lifts and compact at optimum moisture d. May protect from cracking with mulch e. Slurry method undesirable due to flocculation time and uniformity f. POURING A FEW BAGS OVER THE SIDE OF A BOAT INTO THE WATER IS A COMPLETE WASTE OF TIME AND MONEY. C. Non-Dispersed Clays 1. Adequate clay content, but "honeycomb" structure allows seepage 2. Addition of certain salts "disperses" this structure a. Generally, sodium salts increase dispersion, shrink-swell b. Calcium salts decrease shrink-swell but may provide some dispersion 3. Chemical treatment (mix similar to bentonite) a. Soils: 50% fines, 15% clay < 0.002 mm b. NaCl, TSPP, STPP, Soda Ash D. Liners and Membranes 1. Work in most conditions 2. Usually polyethylene, vinyl, or butyl rubber 3. Control puncture from vegetation, livestock 4. Meet NRCS min. criteria and manufacturer's recommendations 5. Concrete, asphalt and soil cement also used E. Large Voids - Rock Cavities 1. Clay blanket may work for very low flow rates 2. Grout or similar material 3. Liners III. Recommend lab analysis (Lincoln SML) for compaction, bentonite, chemical methods IV. Material Costs (Last known) A. Bentonite 1. Bulk: $50/ton 2. 100 lb. Bags: $80/ton 3. Shipping: $50-60/ton within 100 mi. radius B. Chemicals 1. Soda Ash (Na2Co3): $6.75/50lb. Bag 2. TSPP: $92/100lb. Add freight V. An additional method is to concentrate and feed cattle or hogs, feeding grains and hay in the permanent pool area. The livestock will produce a lot of organic matter, salts and compaction. Be sure to allow an area for the livestock to get to in case pond fills with water.
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