What to do when a slow leak is possibly behind massive boulders

[Pond Perseverance]

Hello! Thank you for reading, I’m new to Garden Pond Forum and curious if anyone has any ideas. Background...we have a two pond/3 waterfall feature in our backyard that was installed by previous owners. They also planted aspens around the ponds... so you can imagine how well that went. Last year during quarantine I was able to successfully patch/repair our bottom pond (the aspen roots had punctured the flexible liner), installed a Savio Skimmerfilter, and installed a PondMax pressure filter/UV clarifier. I was also able to move up to the second pond and make the edges more defined and repaired a few visible holes. It was a busy year and I have learned a lot.
This week I started back at it, and with great disappointment realized I now have a leak at the 2” mark of the base of the middle (second) pond. It could have been caused during my repair and repositioning of rocks last summer, or it could be caused by a new root puncture (aspens have been killed off via poison for 1.5 years now however there are a few conifers around this pond). It is a slow leak, I have tried the milk method on a non-windy day and the water just becomes cloudy over time with no movement or leak detected. There are some massive boulders at the back of the pond (see attached picture) that are too heavy to be moved.
First question... does anyone have ideas on how to determine where a slow leak is located?
Second question... what are my options now since we will not be able to reposition and check behind the massive boulders at the back? I’m assuming filling the pond with cement up to 3” wouldn’t work, but could it? Is there a product out there for this type of pond issue?
My plan now is to begin to pull apart my work from last year and inspect visually. I also think I could refill the pond (after removing small boulders along edge) and examine for leaks again.
Thank you so much for anyone reading and able to offer thoughts!

 

[brokensword]

most leaks are from waterfalls and/or the plumbing. First, turn off the water fall and see if it still leaks. If so, then it's not the water fall. If it stops, you know you're going to have to think about moving those boulders and looking for where it's getting out. If that's where your water fall is, you SHOULD have a liner under it all; perhaps the sides of the 'underlaid liner' isn't high enough to hold the leak around your rocks. If this is the leak area after all, you could figure on moving only the top surface portion of rocks and laying a liner under those, all while encapsulating any water fall and plumbing. In other words, create a new underlay area to catch the water your current situation is not. Then you can put the those rocks back.

Check for any leaking plumbing lines including the connections. If you think you have a leak in the pond at the 2" level, if you turn off the pond pump and let it leak until it stops, this will confirm exactly where your leak is along that perimeter. Then the fun starts as you'll have to inspect that line all around until you find it.

You say you fixed a leak in the pond bottom; it's quite possible that fix is still/leaking again. If you turn the pond pump off, and the water level continues to go down, you can suspect that repair.

Not sure re your idea on '3" concrete all around'; with a pond liner, you don't use cement for that, unless you mean liner glue/cement? You can patch after you find where the leak is.

Hope this helps.

 

[Pond Perseverance]

Thanks for attempting to answer this one. All water for the lower pond (working pond) is currently being rerouted around the middle pond (problem pond) so mechanics/plumbing is not affecting this leak.
After a 24 hour rest, the leak line holds at 2” from the bottom of the problem pond. Do you (or any other forum members) know how to locate a slow leak if you cannot go around the entire perimeter to inspect (there a 6 large boulders too heavy to move)?
If the leak is behind the heavy boulders, is there a way to “patch” a small hole you cannot reach? Wishful thinking I know, but I'm trying to exhaust all my options before doing the unthinkable of having to fill in the pond and call it quits.
If I can’t find a leak upon visual inspection of the edges I corrected last year, I could try and dig down behind the big boulders, but I don’t even want to think about that right now!

 

[addy1]

Welcome to our forum!

Do you have any friends around? With one of those moving furniture straps you could move those boulders with two, three people. Put down some padding roll the rock onto the strap and move it. Or just lay down some padding and roll the rocks to a different area to inspect. It will take a bit of work, but can be done. Make sure padding is down so you don't make new holes.

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[GBBUDD]

Another trick that you can do is to fill in the area around the rock and roll it out of the way to inspect for the leak.
It sounds as if you have shut down the pond and let the water drop to where it stopped dropping on its own ?
I did see a product I may have even booked marked it but I don't see it right now. If was similar to bentonite where you placed it in the pond and let it leak and from what I gathered it eventualy made the soil water tight as the leak area. Is it what they claim I have no idea. Can fish be in the pond I doubt it.
But like @addy1 stated yes those boulders are not one man but they are 3 or 4 men boulders. And using moving straps or even non woven fabric making a sling is a possibility.

Feel around the pond walls where your leak is the ground should feel considerably softer starting at the bottom can at least give a hint what side it may be on then work your way around .

 

[brokensword]

and it might be MORE work/$$ to fill in than to move a couple of rocks.

 

[addy1]

I would move the rocks, they are neat ones, but when putting back make sure something is under them.

 

[mgmine]

It was my pond I would bite the bullet and start over. It looks to be fairly small so with a day's work you could move all the rocks including the bigger ones. Those can be moved by using a 6-foot pry bar, especially if you are not concerned about the liner. Once it cleared out redesign the pond and put in a new liner. But before the liner put in some very heavy-duty padding. In my pond, I used a scrap vinyl liner from a swimming pool and then on top of that I put some old carpeting from the curb. I would also get rid of all the small rocks that don't look like the bigger ones. In nature, you wouldn't find a pond or stream with mixed varieties like those. The job could end up taking a week but you'll easily spend that amount of time trying to work around with what you have. In the end, it will be your pond and you will know what has been done and how the plumbing has been run. It will look like what you want it to look like.

 

[Pond Perseverance]

Wow! This is so incredible to get these responses. Thank you all. I can now confirm that there is no easy fix to this pond! That is all I needed to hear. So now it looks like we will be recruiting our strong friends to come move rocks with us (thanks for all the great ideas on moving big boulders) and then I can inspect liner. I wish I could replace liner and reinforce underneath... you’re right that it would be so good to know it was all of our own work (I have yet to find any underlay under this pond liner!).
Great feedback about taking care with moving boulders, checking behind liner for moisture, and pushing down on liner to check for softness of soil in order to locate leak.
Any suggestions about what padding to put under boulders resting on top of liner (to protect liner)? Needs to be safe for fish since the pond below will hold a few fish.

 

[Jhn]

I would use at least 8oz non woven filter fabric (it is incredibly tough stuff)under those rocks and under the liner if you reinstall a new liner, pretty much making a sandwich out of the liner with the fabric. Under the rocks you can fold the nonwoven fabric up into a pad to give plenty of cushion if the rock has sharp edge.

 

[addy1]

I have used extra liner below some big rocks. I do have a few in the big pond, a bunch in the stream.

 

[j.w]

@Pond Perseverance

 

[brokensword]

if your liner is hdrpe, it's more than possible you wouldn't have any underlayment as it can be used that way and is recommended to use as is unless you have sharp edges to protect against. If epdm, yeah, you should have some underlayment. Hope this goes well and you can enjoy the pond again.

 

[GBBUDD]

and it might be MORE work/$$ to fill in than to move a couple of rocks.

by fill it in i mean with fabric carpet cardboard what ever works to get the deeper area next tot he rock flush and then just roll it . but again if your down's have fabric under those rocks you'll want to roll it onto a thick mat of fabric to protect the liner.

 

[kate gusky]

Hello! Thank you for reading, I’m new to Garden Pond Forum and curious if anyone has any ideas. Background...we have a two pond/3 waterfall feature in our backyard that was installed by previous owners. They also planted aspens around the ponds... so you can imagine how well that went. Last year during quarantine I was able to successfully patch/repair our bottom pond (the aspen roots had punctured the flexible liner), installed a Savio Skimmerfilter, and installed a PondMax pressure filter/UV clarifier. I was also able to move up to the second pond and make the edges more defined and repaired a few visible holes. It was a busy year and I have learned a lot.
This week I started back at it, and with great disappointment realized I now have a leak at the 2” mark of the base of the middle (second) pond. It could have been caused during my repair and repositioning of rocks last summer, or it could be caused by a new root puncture (aspens have been killed off via poison for 1.5 years now however there are a few conifers around this pond). It is a slow leak, I have tried the milk method on a non-windy day and the water just becomes cloudy over time with no movement or leak detected. There are some massive boulders at the back of the pond (see attached picture) that are too heavy to be moved.
First question... does anyone have ideas on how to determine where a slow leak is located?
Second question... what are my options now since we will not be able to reposition and check behind the massive boulders at the back? I’m assuming filling the pond with cement up to 3” wouldn’t work, but could it? Is there a product out there for this type of pond issue?
My plan now is to begin to pull apart my work from last year and inspect visually. I also think I could refill the pond (after removing small boulders along edge) and examine for leaks again.
Thank you so much for anyone reading and able to offer thoughts!