Pond Liner options 3

[sketchhwyman]

I am designing a pocket pond here in NY, and I need a pond liner to sustain the permanent pool. NYSDEC Stormwater Manual lists acceptable options: (a) 6-12" of clay soil (b) 30 mil polyliner (c) bentonite (d) chemical additives.

I'm looking for advice on performance/cost benefits for the different options and which in your experience is the best. Thanks.

 

[SlideRuleEra]

We have used "Bentomat Claymax", a geotextile/bentonite product for to line large ash ponds at electric power stations. It looks an feels like a carpet. There are no seams to seal, just ovelap the layers. Being bentonite-based, it is self-healing for small area of damage. For larger damaged areas, just lay a "patch" over the bad spot. Very easy to install - but you do need dry weather. Also need to place material (typically one foot of soil) on top of it immediately to hold it in place. Performance is good. Here is a link

http://www.cetco.com/lte/Content/pdf/TRZ-400 Series PDF/TR-402.pdf

http://www.SlideRuleEra.net

 

[sketchhwyman]

Thank you SlideRuleEra. Is it economical to install in a very small pond (the one I am designing now is only about 0.15 acres in size)? Also, any experience installing it in a bedrock situation? It looks like the surface needs to be well prepared and smooth, though this is surely the case with any type of liner you would install.

 

[DMcGrath]

Once you choose a liner system, providing protection for it is key. 12" or more of soil or sand on top will usually do the trick, more if the pond will be cleaned out periodically. I also have spec'd GCL (Geosynthetic Clay Liner) in a small pond and it works well. We also installed a "warning tape" of sorts 12" above the liner to prevent damage during cleaning.

30-mil poly liner will hold water just fine, but it needs to be protected from damage. If not covered with soil it will A) be ugly and B) eventually be full of holes. Cost per SF varies, but for a small job it will be significantly higher (mobilization costs, etc).

You could amend the existing soils with bentonite, and use that as a relatively impervious barrier. Depending on your soil types, 4% to 8% by weight ought to do the trick. If retaining a permanent pool is the only issue and a small amount of seepage is OK (no environmental issues) then this may be a cost-effective way to go. If I remember correctly, granular Bentonite currently sells for about $350/ton. Figure your pond liner volume (6" thick is probably fine), then how much bentonite to add. It has to be added and properly mixed in to the native soils, then compacted for it to be effective. It is a pretty low-tech process than any good earthwork contractor can do.

 

[SlideRuleEra]

sketchhwyman - The ponds where we used Bentomat Claymax were large - dozens of acres. Also, they were in areas without rock. For a small pond, like you are describing, a polyliner is probably competitive. Maybe you could give bidders options on which type liner to use - then evaluate the bids before issuing the construction contract.

Good comments from DMcGrath. Our experiences with bentonite/soil mix are essentially the same.

http://www.SlideRuleEra.net

 

[dik]

Can you use an EPDM membrane?

Dik

 

[blueoak]

Do you have any good clay in the area? Liner systems are typically when you are protecting groundwater or for water storage in arid regions. If you have clay, that will most likely be the most economical and probaly least maintenance in the long run. I also might ask a soil lab if fly ash or some other additive would work to compare to liners. The one thing about synthetic liners I have seen is that you do want to keep them submerged for a longer life. This seems more true in the winter when you can get damage due to ice.
If you can run some storm drains to it and pick up irrigation water from lawns you may be able to sustain your pool, especially because it seems you get a lot of rain in New York.