I have problem with leakage in Raw

[Gtoyo]

I have problem with leakage in Raw water pond lining with 1mm.HDPE SHEETwith welding joint type. My pond was 90 m. by 45 m.water level is 3.5 m. The water level is lower 1.2 mm./hour which is 2.88 cm/day. My point is we cannt find the criteria that this is accepatble for such kind of this linning or not.
Does anyone out there has experience with acceptance criteria of this HDPE sheet. Is there any sources that I can reference to?.
My Site condition : avg.temp 32deg.c(dry bulb), Humidity 70% wind 3m/s dew point 20deg.c

Thanks

 

[KRSServices]

The manufacturer of the sheet has all the relevant data. Is the pond currently leaking? or is this a new design?

Notwithstanding the liner design (clays, soil cover on liner), I would think the liner may be a little thin based on the overall depth and area. Over the longterm, stretching (and tearing) of the HDPE will be a problem. For Liner information, I use NILEX at

http://www.nilex.com

They should be able to assist you.
KRS Services

http://www.krs-services.com

 

[Gtoyo]

KRSServices
This pond is currently leaking, what I have no idea is Is this leaking quantity is normal acceptable for such kind of this linning. Also, I understand that there shall be some evaporation. how can I calculate this figure.

Thanks

 

[KRSServices]

Evaporation, at best is a guess based on cyclical weather patterns. Rates of evaporation vary with sun/wind/precipitation. I myself have not factored evaporation as a specific calculation, rather, I have integrated it into my treatment flow calculations. Usually, depending on the surface area, I calculate this loss as a very small percentage of the total flow. Regardless though, from a maintenance perspective, you must alwys expect a small amount of leakage, particularly with older ponds. They are incredibly expensive to repair and quite often I have found it is better to monitor for berm failure, major seepage (ie: ponding of water outside the berm) or environmental damage (migration of undesirable compunds into groundwater source). If it is raw (untreated) water containment versus raw effluent, and there are no visible signs of failure, I would monitor rather than try to calculate an acceptable leakage rate because, if your pond is slightly over your calculated limit, what then? Your option would still be to monitor and wait for signs of damage, would it not? KRS Services

http://www.krs-services.com

 

[nealt]

Gtoyo:

Typical permeability values for HDPE membrane liners is on the order of 1x10^-13 cm/sec. Evaporation can certainly be a factor, but if the pond has experienced a sustained "loss" rate of 2.88 cm/day, there is probably another reason. You probably have a punctured liner or a failure in one or more of the welded joints. If this is the case, the only way to locate and repair the leaks is to drain the pond and walk every square foot of the liner. You did not mention whether you have any intended inflow/outflow from the pond. If you do, a water balance will be required to determine if you do in fact have a leak. If you attempt to calculate a water balance, you will need accurate as-built geometry on the pond as earthen ponds are never built exactly to plan. In my experience, the as-built volume of an earthen pond the size you describe can easily be 5%-6% different from the design.

 

[Gtoyo]

KRSServices, nealt
Thank you for your helpful hints.
We checked the pond by check depth of water in various points along the pond,as nealt said it is diificult to check exact volume of pond. The problem is the client may not accept this pond as they quote that have to pay for additional water to fill in this pond regarding to this loss.

Do you have any suggests.

 

[KRSServices]

I certainly do. I can speak to you directly, or your client on this. However, failing that, it comes down to simple economics. What does it cost your client to add water ($/m3). Extrapolate out an evaporation factor. From your numbers it works out to a loss of about 116 m3 per day. For raw water, I assume that it would be pennies per/m3. Using your dimensions and a loss rate of 2.88 cm/day (or just a little over an inch at say $0.10/m3, it works out to about $11.00 per day or about $4,200 per year. Would this cost be within acceptable operating costs of the utility?
Of course this would change in accordance with the pumping cost. How does that figure then compare to the total usage cost in the pond? How does that cost compare with the cost of having to drain, desludge (if required), locate tears and repair the liner in the pond?

I would wager that the pond loss is a fraction of the system losses in the distribution system, and those losses by comparison are much more costly (if dealing with treated or potable water). Unless the soils under the pond are highly porous, such as a native granular soil, a direct loss of 116 m3/day (as a single failure) should show up someplace. If the loss is cumulative from several small (stretch) rips and seam/joint tears in the liner then you will have to assume sectional repairs - and those are costly. This brings up another point though, how old is the pond? Is the liner due to be replaced soon and is the leakage currently being experienced a function of an aging liner?

I feel the approach to your client should deal with the issue of costs in this matter. Assuming no berm or structural failures, they should balance out the cost of examining and repairing the liner, postponing or leaving until evidence of leakage is present. It could very well be that you have several small leaks and evaporation. Finally, if the pond was leak proof how much loss to evaporation would be present on average? Does the different (your loss) actually merit further action being taken, or is it an achademic exercise? Let me know how it shakes out! KRS Services

http://www.krs-services.com

 

[envscout]

You might give Quality Lining Company a call. Don't have contact info readily available but I know they have a website and you can likely find it via a search engine.