Pond Boss Forums POND CONSTRUCTION Selecting a site Test hole

How deep and how big around does a test hole need to be? Also how long should it hold 5 gallons of water?

IMO, ideally, it should be as deep as you expect or want yer pond to be. you should examine the soil that will eventually form the bottom of the pond. if no one is entering the excavation it can be quite narrow (the width of a backhoe bucket). a good operator w/ an extend-a-hoe should be able to get at least 15 feet deep. if somebody plans on going in, it needs to be big around enough to do that safely. IIRC, OSHA requirements for unshored trenches is only 4 feet. if you dont shore than it should be benched in terraces. any water put in should just "pond" in the bottom and still be there the next morning. if you have part clay soils (say a silt/clay mix), and water slowly seeps out overnight it could be you just need good compaction of those soils when you build the pond, or you may need additional clay (which could be found on-site based on test pit results) to compact with the native soils at the desired pond depth.

post caveat.....i am no expert, just my 2c.
let some others chime in here.

I'm no more expert than DIED, but here's my $0.02:

I would dig down as far as the bottom of the pond, or deeper if it was needed to find suitable clay for sealing. You're looking for good soils (clay) to use to hold water and bad soils (sand, gravel, organic layers like peat, bedrock) which would be prone to leaking, with the hope of lots of good and not too much bad. You should be getting the idea on how deep you will have to go to remove topsoil or other less desirable material on top, and if there exists sufficient quantities of clay for sealing.

The test hole doesn't need to hold water itself, for the reasons DIED gave, but should show you if a pond can be constructed with proper techniques using the materials on hand which WILL hold water. Or you may find the site has very unsuitable soils, and be out the cost of the test holes instead of a major pond excavation effort.