Hi Shawn,
just a couple comments, and please pardon me if i missed something in the above posts.....a couple questions first:
1) how long was it after the pond was built (and filled) did the water begin flowing below the dam? and that you noticed wetness on downstream side of dam?
2) what is the substrate of your pond? is it soil or bedrock?
your situation sounds to me like a hydraulic pressure issue, once the pond was filled, you had a new and improved hydrostatic force on the substrate on the pond side which could be affecting the flow of shallow groundwater causing it to moisten your downstream dam material and create a flow (the spring) where there is no dam material present to keep it from flowing freely....... if you follow me.
in my area, since i have no supplemental water, i would try to figure out how to re-use this water (i.e. pump it back up and let it filter overland back into pond basin). maybe even dig a hole below the "spring" to collect the water for easier pumping.
just a different aspect for you to consider from the left coast
