Fire Pond - No Water

[ptmoss]

I designed a fire pond that got built a couple years ago. During construction the contractor uncovered some fractured ledge that he believes is slowly draining the pond. He believes this is the one area that's draining as the water level was rising until he dredged out this particular area and pulled a large boulder or chunk of ledge out.

The pond has filled up during the spring and stayed full during wetter months, but drained down again after an extended dry period. The total depth when full is 8-10 feet and it loses about 3 feet when it has drained down.

The total size of the pond is about a half-acre. The owner would like to try and fix that one spot and I'm recommending a 45-mil pond liner. While it might be best to try and line the whole pond I think the owner would rather try a spot fix first so we might try a 30' x 30' section.

Anybody tried fixing a leaky pond in this manner? Or even just tried fixing a leaky pond in any manner without sealing the whole pond bottom and sides?

 

[zelgar]

First, I would check to see if the water losses could be attributed to evaporation/lack of recharge. See if you can get information about reservoir levels around the area and see if they experienced similar water level losses.

If it appears that the losses are due to drainage, I would first find out what the price would be to line the entire pond. With such a small area, the amount of liner material would not be extensive. I would evaluate the cost for both PVC and HDPE liners.

I don't know how easy or effective trying to do a spot fix. Anchoring the liner may cause issues. Alternately, you might see if a geotextile containing bentonite clay might work or purchasing some bentonite to mix with the native soils to reduce the permeability of the soils. I'd price out these "spot fix" methods but indicate that the risk would be a lot higher of actually solving the problem.

 

[cvg]

addition of powdered bentonite may be cheaper and is cost effective. You don't need to mix the bentonite with existing soil, just dump it in. Wave and current action will spread it around.

 

[ishvaaag]

If the pond has some structure, the effects on the subsoil of the water already lost should also be given some thought and maybe investigation.

 

[bimr]

If you have not already done so, a geotechnical investigation should be done. Without an investigation, any proposed fix is just an educated guess.

If this is a fire pond, then the matter is a life safety issue and more detailed investigation is warranted.

 

[theCorkster]

Start with reviewing National Resource Conservation Service Soil maps for the site to get an idea of the soils involved. The soil maps typically go to a depth of 60 inches, and can serve as a guide to differentiating soil permeability.

Based on the pond drainage slowing down after 3 feet, the problem is likely associated with a change in the upper 3 feet of soil. Was the pond profile changed anywhere?

If you can limit the source to the upper 3 feet, why fix the lower 5 to 7 feet of the sides, or the bottom?

Map the soil types in the upper 3 feet and look for coarse grained soils (clean sands, clean gravels, etc.) as a likely cause. Depending on the soil, roto-till in bentonite and bentonite/sand to help seal. Don't over - bentonite as then you'll have cracking during the dry seasons that will leak!

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