Andy,

This is way out of my league, but I went looking for "pond marker dyes" and ran across this link here in USA. I would think there is a similar company / source there.

One possible problem I foresee could be the dye leaching out before making its appearance on the ground.

LP

Here is a link that might be useful: PondDyes.com

Hey Andy. You will likely get more responses on the United Kingdom version of this forum. They seem to have more over there than we do here, but I'll give a try to a few possibilities. You don't say how the clay was compacted or if any Montmillorite (Bentonite) clay was used. If there was an inclusion (a different type of soil or roots) that could easily be where the leak is located. We just had a discussion about puddling clay on this forum a few weeks ago for a pond and much info came from sites about Dew ponds in the U.K. One of the most common locations for leaks was the top edge of the pond which could act as a wick if it was not constructed properly. I never had much luck with using dyes in the water to find a leak. It mixed much too quickly. One material I have found useful was a handful of fine, dry, powdered clay scattered on the surface. Calcium Bentonite is quite good for this since it can be purchased as a fish tonic or cosmetic base as well as a construction material. If the water is reasonably clear it should work well for you. If not, it needs rethinking. Some one suggested dry milk powder to me. I didn't try it but it sounded reasonable and would be inexpensive. The Bentonite should be available at home and garden supply stores or through a well digger, which is where I found it. The added advantage is that the Bentonite can be used to seal the leak when you find it. Check on this forum for the Puddling Clay thread and do a search for Dew ponds, one of which is linked in the puddling thread. Sandy

Here is a link that might be useful: Puddling clay

Andy, I am doing some arithmitic here and this is what I see:

You have 1-2 feet of topsoil, 3-4 feet of sand and gravel and them clay starting from 4-6 feet below grade or grass with a total depth of around 7 feet. Does this mean that as you look at your excavated pond you see a profile of mostly topsoil and sand and gravel with a shallow clay-lined basin at the bottom?

Some further description and explanation would be helpful in looking at your problem.

Sounds interesting, hope to hear back.

Mike

Detailed info was given to you by engineers and pond folks all well versed in mud ponds and how to find and fix leaks in an other online forum a week before you posted this same stuff once again. It does not matter what forum you use, the answers will be the same anyway you look at it. Answers are not usually geared to being the cheapest or easiest route, and odds are if a route short of what was given is taken, you'll always have a leaky pond which IMHO is worse than a leaky bucket!

Finding leaks is really hard. Check to be sure some of the liner is not caught under a rock or plants are wicking up the moisture somewhere. I put a link there for you.

Here is a link that might be useful: How To Fix A Leaky Pond