I had a test hole dug a few weeks ago in the area that I would like to eventually build a larger tank. The soil is black dirt and clay to about 4 feet, and then a lot of white rock below that. I mainly dug the hole to see how well it would hold water, but it raised a few questions in my mind about what can really be learned from it.
There are many other tanks in the area built on the same soil, most of which seem to hold water very well. The farmer that runs our place has a tank on his property built on almost solid rock that's been there for 20 years and never gone dry. When I talked to him about the construction techniques of his tank, it seems that he broke just about every rule I've read in the ag handbook or on this site, yet he has a nice looking tank that holds water and that doesn't appear to leak. He told the dozer man to put the ripper down until he got the depth that we wanted, didn't pack dirt on it, didn't key the dam...but it worked. I realize that his case is probably more luck than anything else, but it illustrates why I question what I can tell from the test hole that I now have.
Below are a couple of pictures of the hole when it was dug, and about 2 weeks later after a rain.
It just seems that there are so many variables involved, that you can't really tell from a test hole whether or not your tank will hold. The test hole may seem to hold water, but what about when you build a larger tank, with more surface area and much greater hydraulic pressure? I asked the dozer man whether or not he thought it would hold water and he kind of shrugged and said, "Maybe. Maybe not." Honestly, I kind of appreciated that answer because it seems that he's exactly right.
So...the question is...how do you correlate what you see in a test hole vs. what you might expect with a larger tank?
