LittleFish, Thanks for the update!
You didn't mention them, but are your springs still visibly flowing? If so, let the water drain to it's low point and that will be the level of your leak source. Mark the level and siphon/pump off another 2 feet or more of water and if you're very lucky, I'm not, there will be holes were the leak(s) occur. Even if they are not visible you can compact that area very well and possibly seal the seapage.
