Retention ponds

[bank]

If the bottom of a proposed retention pond/water feature will be below the water table, are there any factors, environmental or otherwise, that would require (or preclude) the use of a clay liner or similar product to separate the pond water from the groundwater?

We plan on using City water to maintain a constant level in the pond. Is it improper to have it mixing with groundwater in the pond?

 

[zelgar]

To be on the safe side, I'd contact your State's Environmental Agency - Water Division and possible the Department of Natural Resources - Water Division (for some States both agencies are combined).

 

[bimr]

You would want to minimize the loss of water from your water feature. Most users do not have unlimited water resources. It would be better to know beforehand what is going to happen to the water in the pond before it is built rather than afterward.

Are you in a flood area where the water level may rise from an adjacent river? Ground water levels are not constant.

 

[tsgrue]

.

A few items...

1) If the bottom is below the soil water table, then you will have inflow from the soil water table unless it is totally sealed (your mention of such) or the local water table is pumped down - ready constant energy cost and maintenance burden. There will also be inflow pressure unless drawn down.

2) Wht would you fill a retention pond with potable water (read very wasteful)? Is this intended for a "water feature" and not stormwater infiltration?

3) Once potable water comes in contact with nonpotable water, it is no longer potable.

4) You'll find lots of information on your general subject searching older posts on this site.

Good luck!

.



tsgrue: site engineering, stormwater
management, landscape design, ecosystem
rehabilitation, mathematical simulation

http://hhwq.blogspot.com

 

[jartgo]

I'm not sure why you would want to supplement with potable water. I'm guessing this would be for aesthetic reasons. I would try to design the permanent pool elevation to coincide with the average groundwater level. If it's too deep, you could just line the pond and supplement it with untreated groundwater (the well will require a seperate permit).

In the case of potable water, environmental folks would likely take issue with introducing chlorinated water into the environment. I know where I'm at, even when the quantity is insignificant, discharging chlorinated water (for any reason) to surface water's is a no-no.

There are options for dechlorinating, however, this will further complicate your operation. Not knowing the details of what you're trying to accomplish, I think I'd look for another solution.

 

[Ron]

Forget the potable water supplementation. Design the pond based on the void ratio of the soil replacement. If you pull out 10 cy of soil, 50 to 70 percent of that was soil solid volume....the remaining volume can be used for water storage.

 

[Ryb01]

Another possible scneario to look at may be to consider a wetland/hybrid type of facility vs a wet pond. This could reduce the overall depth of your pond, possibly removing the pond bottom from the ground water table.

 

[Sasmo12]

I agree with Jartgo, a recharge well is the cheaper way to go than treated municipal water. However, if you do go for publicly supplied water, be sure to get a "Water Only" connection so you are not paying for sewer treatment as well.

To accommodate the water feature aesthetics, which is why I assume you are considering a potable water source, you can look into local treatment to control turbidity. Certain chemicals are typically allowed but usually have to be included in an O&M plan. Ensure the pond volume below normal pool elevation can handle normal amounts of sedimentation, which is to be expected.

Also, consider a trophic analysis of the pond. You do not want to get unwanted algal growth after it is put into operation.

If you do decide to utilize an impermeable liner, be sure to consider buoyancy forces. You don't want a cracked liner when the groundwater rises.

And of course, don't forget to take into account evaporation if you are in an area that sees high evaporation rates throughout the year.