I am a contractor in Central IL. I specialize in ponds and no pond seepage is normal. I also think the contractor you have is on the wrong page beacuse I have never and will never charge extra to put a core in. I put a core in every pond that I build beacuse without one, they ALL leak. It is always included in the price. When the contractor says give it time to "seal" that is supposed to mean so the water doesn't seep into the ground. Eventually the ground will stop soaking up the water and your water level will rise. It doesn't mean it will stop leaking past the levee. It could take up to 2 years for your pond to maintain the highest level. But your levee will never seal. You have a problem and it needs fixed. Also, keep in mind that on hot summer days it is normal to lose an inch a day to evaporation.
