All dirt leaks water through it. It is a matter of degree. The amount of leakage is dependant on numerous things. Most of my experience is with dug out ponds that have clay liners or core trenches. Typically if a clay lined pond is leaking when it is first filled, you have soils that were either not compacted properly or not enough good clay liner was installed in the vacinity of the leak.
For a pond built by daming a ravine then I think it is about how much clay compaction occured along the banks and how the dam was built. I would think if you just damed a ravine then expect water to leak through a lot of the side walls especially in areas where the contractor may not have cored and compacted the side walls throughly or properly. Ponds built with a dam typically rely on a lot of water from the water shed to keep them full. Those people with ponds having dams can add more insight to this topic.
Bottom line, if a pond is supposed to be water tight, I do not understand why it will not properly hold water when first filled. Any disturbed soils should be properly compacted so there is no "settle down" period. Sounds to me like the contractor is hoping for some fine clays or particles to get sucked into the seepage areas and slow the water loss. If the seepage is slowed in this manner I would think this "leak spot" would be a very tenuous seal and always susceptable to leakage.
Good dug out, water tight ponds properly built in heavy clay soils in my area basically lose water primarily to evaporation. During extended summer dry periods of 40 to 60 days water loss in these ponds is typically 12" maximum. More loss than that suggest leaks are to blame. A leaky pond is difficult to cheaply and properly fix. THAT IS WHY TAKING TIME IN CHOOSING THE BEST CONTRACTOR AND NOT THE CHEAPEST CONTRACTOR IS VERY VERY IMPORTANT.
Comments from others with experience with slow sealing ponds?
