Above ground springs appearing and disappearing. Normal aquifers are horizontal. That type of movement can indicate special problems.
Historical geology on your little pond is a great big glacier melted, slid down and created Lake Ontario, scraping a limestone basin in the process. Most likely losing size but gaining momentum. Just down the road in Earth's surface is the Howe Caverns, a incredible Karst formation. Your pond resides in between all of this, with a abundace of fractured limestone.
http://www.howecaverns.com/Piping can occur anywhere there is a water passage. If the passage allows dirt and soil to move within it, pretty soon you have piping. This can lead to immediate structural failure. It may show up as a wet spot on your downpond embankment, a sinkhole inside. Maybe a whirlpool. Another bummer in that type of formation is an inverted cone sinkhole. This could start anywhere on your pond bottom, gain momentum and washout into an underground aquifer or empty cavern.
The relevance of do you have ponds around you is most likely they have similar soils. If they did not have any improvements and are holding up fine that is a great indicator for yours.
I'm sure everything will be fine. It's a fantastic accomplishment.
