RE: Sink Hole
A spring, by definition, is where waterdischarges out of the ground. A spring can't suck water into the ground. A recharge area is where the water goes into the ground. A recharge area occurs where you have very permiable soil such as sand or an area of fractured bedrock where water can run in from the surface. If it is a sandy layer, you'll have todig it out to a depth of about 3 feet below the planned bottom of your pond and repack with clay or even a layer of bentinite, which is an extremely water-tight clay. If you have fractured bedrock, you'll have toexcavate it down to the cracks and seal them with bentinite.