"Thanks. I had no idea that springs worked this way. I assumed water would bubble up and fill the pond to ground level!"
It might do that Frogger!
But it might not, that is why the test holes are a good idea before spending all of the money on constructing the pond.
Also, some springs are seasonal. You could have a water level during the wet periods where your pond is full and water is going out of your outlet pipe. However, during the dry periods your pond could drop to the elevation of the spring at the point where it intersects your pond.
If safe, I would leave your test pits open for a year and observe the water level.
However, even that may not indicate the expected water level of your completed pond. Once you construct the pond, the spring will now be losing water to evaporation and seepage. This should not affect a high-volume spring. If you only have a low-volume spring connected to the pond, then your annual pond level will average lower than the water level in your test pits.
