Pond Boss Forums POND CONSTRUCTION Renovating a Pond or Lake? Black Plastic Sheeting

Hi all.

Some of you have seen me here before, many times, seeking advice and updating the forum about a leaking lake I've been working on for about 20 years now. Yes, twenty years.

We left off with the contractor coming back for the third or fourth time in Feb of 2012. We dug into the levee and found sand. So, they took a huge track hoe and a dozer and dug out the sand, which took nearly two weeks. We probably dug sand for over 200 feet down the top of the dam and probably 15 feet wide and mover ten feet deep. We then took a 17 yard dirt pan and filled it back with good clay. The back side of the levee did not show signs of water this year, and I believe we have fixed that problem. We dug a new core ditch in front of the old core ditch just for extra.

Still, it was apparent that the lake was still leaking once I got it full again. I didn't worry too much over this last year since I was prepared to give it the benefit of the doubt and let it settle and self-compact for a year. This is now the near end of year two and although it took longer, the lake eventually dropped to the level where it always falls, and how appears to have quit falling. Right in the same place.

So now it's back to that mystic spot where the leak is. We never have identified exactly where it is. Water must still be getting into a sand vein or pocket someplace and seeping in and around till it leaves, causing the leak. We may go around it with a metal probe, but we've done that many times in the past. We found several sandy areas, but when we dig down with a track hoe, sometimes five feet or more, we hit solid clay that is almost as hard as concrete. We added clay over these areas, but it still wasn't enough. Now, what I think is happening is that the water is getting into these sand veins and routing around to a leaky spot in a different location, and draining out from there.

The only thing I can think of now is to drain it down another couple of feet to the bottom pond basin. When we get it that low it looks like a bowl on the bottom. It's very distinct where the basin is. I’ve never known that to leak. In fact, I’ve never known it to leak more than where the level is now. There is something at that elevation, somewhere, that we can’t find that is causing the leak. Now, I think my best option is to plate over the known sandy areas with more clay soil, lay plastic all around the lake to cover that band, and then add clay soil on top of the plastic.

I give a neighbor all the hay he wants in return for me getting my pastures mowed every year. He has a bulldozer, a good sized John Deere and a 5 yard dirt pan. He'll do the work free if I buy the diesel, so we already struck that deal.

I can order 10 mil black plastic PVC sheeting, 20 x 100 for around $140 a roll. This time I want to overlay as much of the lake bottom as I can. And, I want to overlap it, so the width will be around 35 feet wide, instead of 40. This would need a five feet over lap.

The plan now is to open the gate valve and drain the lake down to pools basin level soon. Then take the dozer and push my fish holding brush piles out into the basin. I won't lose much cover -- it will just be out farther.

Next, I want the dozer to make a smooth surface all around the lake from the basin up to the high water mark. Here, I want to add more clay to the areas I know to be sandy, then lay out the plastic and overlap it. Then, using a front end loader we'll go easy and dump more clay dirt on top of the black plastic. We'll work our way around on mats, and also do a lot of shovel work to cover the plastic at least six inches deep.

To my thinking, a five foot overlap should be plenty to keep water from running between the plastic sheets, especially since we will have it weighted with clay dirt. I can't imagine more than a tiny seepage, if there is a seepage at all.

Before we start I wanted to ask some of the pros here again about my plan and the use of plastic in a lake bed. Will a five foot overlap be more than enough to stop anything but a tiny seepage? Seems to me it would be virtually waterproof.

We'll be going about 800 feet, maybe up to 1,000 so I can't find, or think of, any cost effective way to join the overlapped pieces with an adhesive, such as tape or roofing tar. Even then, I don't feel like either would last long under water.

I can take a modified one point chisel plough and pull it around with a small tractor, pulling a small trench right where I want the over lap to be. Then when I lay the plastic and overlap it I could anchor it in the trench with 1/2 rebar. That would crimp it pretty good, and I just can't imagine how there could be any significant seepage with that arrangement.

Also, I'd like information from the forum members on how long will 10 mil black plastic sheeting last under dirt, under water, and never being exposed to sunlight or harsh temp changes. I hear that plastic bags last decades in land fills, with no significant break-up. I know PVC is inorganic and will lever truly compost, but from what I'm reading, if you have it underground that it last indefinitely.

We have the dozer on site now, and the tractor and dirt pan will be coming over next week. We'll have that, plus two or three tractors with loaders that we can use to dump clay dirt on top of the plastic. I might even use 4 x 8 plywood sheets as a mat for the tractors to get out on the dirt that is covering the plastic, so they can gradually work their way farther and farther out. I can't imagine how the plastic would even feel the pressure of a tractor tire over them if I use mats like this.

So there you have it. The saga of the leaky lake continues. I've tried everything else, but I can't see how it could leak if I cover the bottom with plastic. Still, I'd like your thoughts.

Oh, and for those of you who asked months ago about the contractor coming back and the fee he charged for digging out the sand and hauling and packing in clay dirt, we had a firm yet friendly meeting of the minds and he didn't charge me. We did some other work around the farm, which I paid for, but the discount would be just about right to cover the cost of the back hoe, the dozer, and the dirt pan to correct the sand levee problem. Neither of us was totally happy, but I understood his side and he understood mine, and we've done a lot of business down through the years and when I mentioned a discount he didn't argue. I made an offer, he countered, I accepted, and then paid him with a hold harmless release from any more liability on the pond .

That's the update on the leaky lake saga. Let me know your thoughts and suggestions, especially on lapping the plastic sheets, and how long they should last underground, underwater, being packed and insulated from extremes in weather and any contact with direct sunlight. I'm guessing in my climate that if I could probe down 6-12 inches with a thermometer in any local lake bottom that the temps would be in the 70s almost all the time.

Some of you have a world of experience with soils and lake constructions, and some of you just might offer suggestions that make all of this work better. I’ll have a tone of pictures and video during this renovation, and I’m hoping that not only will it fix my leaky lake, but that it will be of benefit to others with a similar problem.

Thanks in advance, and I really look forward to hearing from you.

“Bill”

To be honest, I did not read you whole post (I have a short attention span). If you are not aware, the leak is not necessarily at the level where the lake stops dropping. The lake may be connected to the water table at any place in the basin, or there could be a connection with the sand vein anywhere in the basin such that the water enters the vein but somewhere back under the soil must rise to the "lower" water level before continuing down stream.

P.S. I am no expert, but have contracted a couple successful ponds and a few wetlands. The only one that leaks is a wetland built as part of a mitigation project by "experts" on land that we volunteered, and we told them it would since they did not disrupt the field tiles properly or core the berm. Fortunately it gets enough inflow to make it a nice seasonal wetland anyway. Not sure if it will pass their criteria though.

I must say that I also agree with RAH. The water drops to that level all the time. It might be a result that the water pressure, caused by the weight of the water, is diminished at that level and can't push thru a vein that might be 5' down, 10', 15' or wherever deep.

I would still be leery about the plastic being separate pieces. With the weight of water and pressure, it sure seems like it would find any possible leak, no matter how small or thin. It don't take much, but you also have to weigh what leaks to what water is coming into the pond.

It is often mentioned that its better to build a pond the right way the first time, because it is very difficult to re-do one. Then, to have to re-do it many times is really discouraging, etc. I would think at this point, do it right and consider lining the whole pond with clay, and compacting it, with a sheepsfoot roller. Just lining spots with clay may not work either, because if it isn't brought to solid clay it just will seep underneath it back to a sand vein.

I agree with RAH and fish n chips. You don't see posts and threads about using plastic sheeting to line ponds and fix leaks because it isn't used. I'm not saying that it wouldn't work, and I'm not saying that it WILL work. I'm saying that over time, historically, the only way to seal a pond well enough to hold water is to plate the WHOLE pond basin, from the very bottom to above the high water level with clay, properly compacted to a thickness of 18" to 24" if the whole pond basin isn't comprised of clay. ANY sandy areas need to be excavated out to good clay and repacked with clay, just like you did with the dam.

That is what has proven to work. Are you willing to go to this expenxe and take the time to do this, with the knowledge of being a forerunner in this technique that might not work? Or would you rather go with a technique that has proven to work if followed?

First, you're going to have to read my entire post to see what I actually said before you can know how to answer. I mentioned a lot of things that you covered.

I've had the best soil experts in my area, including the soil conservation, lake designers, several respected contractors, and government agents, and etc. In the beginning I got a soil scientist to evaluate the lake area and he said it was ideal. We spent part of one afternoon driving around the site boring test holes with a tractor and an auger to check the soil composition and he said the dirt was excellent. How we missed ay sand, I 'll never know unless it was too deep for us to detect.

So I did build this lake the "right" way in the beginning, with a good contractor. Most people thought I "over-built" it
just to be on the safe side.

I've also done every thing we've done the "right" way since the leak was discovered. I've plated over the levee with 2-4' of clay. Later I did more test drilling and we dug out most of the levee to remove any sand that was there. I never noticed anything wrong with the fill dirt back at the time of construction, but they could have done it when I wasn't there. Regardless, there is no evidence of a leak there now.

While we were at it we did a secondary core ditch, even though there was no evidence it was leaking there, but we did it just to be on the safe side again.

We DID dig out all the sand in the sand pockets and veins we found, and packed it with clay. Then we plated over it with even more clay. You can't dig all the sand out, because every lake and pond in my state has sand in it somewhere. We took a back hoe and trenched around the areas we found sand pockets when we probed and backfilled and plated over them. We've already plated with clay, as you suggested.

I can only get down to my low pool level. If I get much beyond the pool level I'm afraid it would hurt the fish. Still, I think I may can add clay to that point to displace some of the water than might be causing some pressure. However, I've had soil and lake experts look at the lake and all of them say there is not enough head to force water out. It looks just like a perfectly good lake site in all regards.

As far as people not using plastic to line a lake, they do it all the time. I see lagoons and other lakes with a solid lining of plastic sheeting scattered around for many uses. People use plastic all the time for things like this, and they also build smaller ponds out of it for koi, too. Here's one example. http://informedfarmers.com/using-liners-to-stop/ And as the article says, it's 100% effective at stopping leaks. There are companies who specialize in this very thing. There's even a tarp company out there that sells waterproof tarps that were used as billboard signs. They have customers that line leaky lake beds with them and it works.

As far as the solid layer of seamed 45 mil plastic, I don't have the budget for that, and if I did it would require me to drain all the fish out to do it.

I want to add more clay to the suspect areas, as I said in my post. Then add black plastic, and then add more clay on top of that.

I was mainly curious if anyone else here had tried using black plastic commonly found in hardware stores.

You did mentioned the pressure on a lake bottom that can contribute to water being forced out. That's another reason I'll be adding as much clay as I can before adding the plastic. The more soil I can get in the lake bed, the less water there will be, which should decrease the water pressure being exerted downward.

The main thing I wanted to ask here is if anyone else had used black plastic sheeting. I also wanted to know if anyone had info telling how long it will last sealed underground. Again, we all know it will hold water. I'm just curious to know for how long.

Thanks again.

DS

No experience with that. Best of luck! Please let us know how it works so we can learn from your experiment. Nothing ventured, nothing gained!

I think I read somewhere on this forum that it doesn't matter if its 1 acre or 1000ac given the same depth has the same amount of pressure.

Yup - Physics - Think scuba - The pressure depends on your depth, independent of whether you are swimming in a pool or the ocean.

IMHO, The use of thin plastic sheeting to seal a small koi pond sounds feasible. Not so much for a larger pond though.

I'm not sure of the size of your pond, but, your plan sounds very labor intensive; prepping the bottom, staging the cover soil, spreading the plastic, placing the cover soil carefully on the plastic, trenching and tucking in the outer edges of the plastic, using mats for the equipment, etc.

Your plan is to only cover the top portion of the pond with plastic. It seems to me that the water may migrate under the bottom edge and rise up the backside of the plastic, thereby rendering the plastic useless. Most lined ponds are 100% lined.

If the pond's sides have much slope at all, the cover soil will possibly slough/slide downwards towards the bottom as the pond fills, due to the cover soil not having any adhesion with the underlying soil. Likely resulting in the plastic being exposed to the elements, hooved animals, etc.

Provided you have clay of sufficient quality, it sounds like you have the equipment necessary to re-line and compact the entire pond, and be done with it.

Having all of that plastic semi-buried in the sub-surface of a leaking pond sounds like a nightmare scenario.

I feel your pain. Recently, I successfully re-lined my leaking pond (knock on wood) using only a small tractor with front bucket and box-blade. You gotta make sure you get good coverage on every square inch. Don't hesitate to apply over-kill.

Good luck, I hope you get it fixed.

As far as your question about degradation, I believe you are correct., in the absence of UV and air exposure, the plastic sheeting should last longer than you. However, there are a few problems...

Easy to puncture with a few stones, sticks, or hooves. One hole is all it takes to render it useless. For the same reason, non welded seams just wont work. The plastic to soil boundary will be teaming with organisms and plenty of water pathways. Water will simply need to travel further with the plastic, that's it.
It doesn't stretch much before it rips. Think settling. That is why most ponds use rubber materials rather than plastic.
Any back pressure from a water table will cause it to lift from the bottom like a large balloon if it isn't buried.

The thing that bothers me is the chance for plastic to float off of the bottom and become an annoyance or eyesore. I hate the stuff in gardens, it is forever pulling up and getting tangled in things.
I have seen advertisements for one huge contiguous sheet of plastic or rubber that can be used for lining waste water lakes, but something that size would have to be placed in new construction, and it is much heavier material than hardware store stuff.

I would guess you have a leak down deep, where the pond and surrounding water table like to neutralize pressures. It is also possible this is two directional flow. When things are wet, water comes in, when dry, it goes out. This makes plugging via ess materials or pouring in clay not work. You would have to compress or pack clay very tightly to stop that.

Have you thought about lowering your expectations of what is considered full pool? You could contour the exposed banks and bring in topsoil, and deal with what you have. No more leak in a sense, just a shallower pond than you hoped for. sometimes a lot less frustrating and expensive to reset the goal.

What others have suggested is likely true if you want the pond fixed, but it means draining and starting over. It doesn't sound like that is something you are willing to do. However, if it works, you can be done with the frustration once and for all, pending a large earthquake.

Yes, I've thought about considering it to be a smaller lake and just live with it. But I haven't given in to that yet.

I don't have any intention of just laying it on the bottom. We're going to haul in more clay for several days and smooth and pack it with a dozer and hopefully a sheepsfoot roller if I can find one close by. I'd like to add enough clay that the clay itself would seal wherever the leak is. To go the extra mile I will then lay the plastic over the clay. To go another extra mile we'll add more clay on top of the plastic. I want to add as much clay as I can to displace as much water as I can. Hopefully this will help with the downward water pressure too.

This was the site of another cattle pond. It held water wonderfully. We never had one minute's trouble out of it. The problem started when I knocked that levee down, back down the hollow about 100 feet, and built a bigger levee. When I got the levee to the height I wanted it, THAT's when we noticed the leak.

I think the water line much have backed up over a hidden sand pocket. We've tried everything to located them, but I think now the thing to do is forget looking for a sand pocket and just plate as much as I can with clay, add plastic, and more clay. I'm going to draw it down to that original pond basin, which does drop off like a bowl, and work it with clay and the plastic all the way around and out. I just stocked it in 2008, so the fishing is getting to the prime stage and I don't want to drain the whole thing to re-work all of it and lose the fish.

DS

I talked to a man today who works for a pond liner company. Selling the material and lining ponds to make them hold water is what they do.

He said the idea seems solid to him. They do the same procedure when lining large projects, but use heavier plastic that is much more expensive. He said the theory is the same, and once the plastic is buried it will accomplish the same thing as their product does, and would last a very long time. Some of the ultra heavy material is only cost feasible for small ponds, like for koi or other backyard ponds and pools.

He was a nice guy and seemed very knowledgeable. He said he'd love to sell me their product, but from what I described that my project would be so expensive if I used their $800 + shipping per roll product it would be very expensive and accomplish the same thing, so he suggested that I go with 10 mil, lap it, and cover it with clay like I suggested. I appreciated his candor and honesty, and that he was trying to help me, not just sell me something.

One thing we discussed is that building contractors commonly use 6 mil black plastic sheeting when framing up to pour a slab for a house. Concrete undergoes quite a chemical transformation in the first few days. If building supply grade black plastic is approved by government back loans, and expected to be a msoiture bartrtier indefinitely, then that is a pretty good endorsement. One could only guess how long it lasts, or how long it would last in a land fill. A LONG time, I'm sure.

As far as all the prep work someone mentioned above, it's really simple. My friend will just push the brush into the low water basin and then track his dozer around the water line where we'll put the plastic. We'll also run a small tractor with a blade on the back, so the site preparation won't be that big of a deal. We'll have three front en loaders to dump the clay on top, and once it's deep enough we'll run the small tractor with the blade over it to smooth and pack it.

The guy I spoke with said he would ask around if anyone else at the company had other ideas, which I appreciated. I'll call him back in a week or so, after I've asked at least one more pond liner company their opinion. If everything goes well I hope to start the middle of October.

DS

I feel for your pond emotions, and I sure hate to be a nay-sayer, but I'm afraid that thin plastic liner will neither last, nor work for very long, if at all. I had some experience several years ago with some similar failed ponds made with pool liner over sand, and covered with sand. It doesn't take much more than a deer wandering in the pond to puncture such a liner. I don't know the thickness of that liner, but pool liner is usually 20-25 mil.

I think that compacted clay is by far the best solution. I don't believe you will be able to put 6-mil plastic sheeting on top of clay, and then adding clay on top of the sheeting. It is just too thin and weak. It will probably puncture and/or rupture with the first load of clay dumped on top. Adding equipment to the equation makes it even worse.

I'm afraid that if you need a liner, it needs to be something like 45-mil EPDM aquatic liner. It is tough, and it stretches under stress. But, compacted clay is still going to give you the best chance of success.

Let me try this again.

I am not going over sand with plastic, and then topping it with more sand. I never said that anywhere in any of these posts.

I have a sand pocked someplace but I don't know where the leak is. We have hauled probably 2,500 yards or more of clay to the lake bed in the last few years. Except for some sand that ran into the lake after rains the last two years there is no solid area of sand in the lake bed. There is probably a thin spot someplace that lets this slow leak keep leaking.

This is not some dramatic fast leaking structure. It takes 6 months for it to leak down to the current level. In the summer time it drops about an inch a day, which is not that drastic. Every year it seems to get a little bit better, as if it is sealing itself off, even though it's doing it very slowly.

We are going to ADD MORE CLAY to the existing lake bed. We are going to level it and spread it as evenly as possible with a dozer so that every exposed inch of the lake bed will get MORE CLAY. I hope this is enough to seal the leak itself. Secondly, the addition of this clay is to displace water to reduce the downward pressure. I AM ADDING MORE CLAY TO THE LAKE BED FIRST. I can't make this any more clear.

Next I will add the 10 mil liner, which has it's own flexibility. I've already discussed this will a pond liner guy and he didn't see a problem with it. He also said the 45 mil EDPM was not necessary on a project like this. I don't think you could even install it on a project like this. I am not using 6 mil plastic. I have 10 mil. When I lap it, it will be 20 mils in some places.

We are going to use front end loaders on small tractors to add clay on top of the plastic. We will add it slowly to the edge and work our way out. We will not be dumping heavy loads of clay onto the bare plastic. We will work our way out on mats, and also use shovels if we have to. There will be no heavy equipment touching the plastic.

The plastic will be under enough clay so that a deer can't possibly step through it. There are no cows. As soon as the layer of clay on top is completed the lake will be filled from a well. The only time the plastic will be exposed is while we are installing it, and we will work it one piece at a time, leaving nothing uncovered.

I'm becoming mystified concerning the participation here. I've never said I'm using 6 mil plastic, and I've never said I'm adding it on top of a sand bottom and adding sand on top. There is obviously a spot somewhere that didn't get enough clay, but we've hauled in tons and tons and tons of clay already. All I'm doing now is sandwiching lapped 10 mil plastic between two layers of clay. I could actually leave the plastic out of the equation, but I can't see how it could hurt to add it, and 10 mil plastic is just as waterproof as 100 mil plastic, and when topped with clay it will last probably just as long.

Everyone here wants to see your pond project succeed just as much as you do, BillLake. Asking for everyone's opinion on your plan is a lot different from asking them to just sign off on a plan that you already have. It sounds to me that your mind is made up, and speaking just for myself, I'm not informed enough to say that your idea won't work...but I'm not able to guarantee success either.

In the end, we all do what we think is best for our individual situations, hopefully, as you are doing, after getting advice from several sources. I wish you the best, and would appreciate updates as to your progress....always interested in learning something new.

Would this be a basic recap of you idea?: Instead of adding a heavy layer of clay, your hopes are to add a little less thickness in clay than a normal procedure. In exchange for less clay you want to add in a layer plastic.

Clay works by binding/knitting together (with a sheepsfoot roller). Pond builders seem to have come up with a number of inches that this works best at. Where I am going with this is if you separate these thicknesses with a layer of plastic will these layers effectiveness be diminished so much that the benefit of adding plastic is negated? I can't answer that, just throwing it out there for consideration.

How many inches of clay of packed clay underneath the plastic is your goal? How many inches of packed clay on top?

BillLake - I apologize for mentioning 6-mil plastic. I'm not sure where I got that.

As for the sand, it used for a couple of reasons in landfills, tankfarms, toxic waste ponds, etc. It is put over compacted clay and or hydrated bentonite. One reason for the sand is that it doesn't fracture as clay can, and it acts as a buffer for sharp objects such as rocks in the clay. In the industrial uses I mentioned above, it also provides for draining leachate if the liner should fracture - something you obviously don't need.

I can fully understand your frustration over this project. It is my belief that everyone here is just trying to keep you from spending a lot of time and money on a technique that has a lot of potential downsides.

Have you talked to Mike Otto about your dilemma? If not, give Pond Boss headquarters a call and setup a phone meeting with Mike. There is nobody with more experience with these types of issues. Plus, Mike is just a fun guy to talk with.