How much clay is needed in sand to hold water.I have yellow -red clay.I put some soil in a class of water,mixed it.The sand settled to the bottom and,I guess the clay is on top.The clay appears to be about 20% of the total.Is this good way to measure this?
Thanks Rick
I recall 35% clay as the "ideal" mixture. Grab a handful and make a ball. Does it hold together? Also, you can dig a hole, fill it with water and refill it once it sinks back into the sides. See what happens. I would always dig a test hole or core to see what I had underground before I committed abunch of $.
Here's a way to test any soil to see if it is suitable:
Using something like a five-gallon bucket, drill several holes along the vertical edge near the bottom of the bucket. Holes of around 3/8th inch work well. Next, fill the bottom of the bucket with four inches of crushed gravel, such as 3/4-minus. On top of the gravel, place about six inches of what ever soil/clay type material you plan to use for the pond. Thoroughly compact this clay layer throughout the bucket, paying particular attention to the edge. Make sure the clay is somewhat moist. Moist enough to make a ball out of the material is about optimum. Now fill the bucket to the rim with water. Cover the bucket with an impervious surface such as plastic. Wait a couple days, then refill the bucket. The soil needs time to saturate with water. Cover the bucket once again. Now wait up to a week to see if the soil will hold water. Obviously you can check after the first day to see if the material failed. Our experience has been that if you lose less than an inch of water after a week in the bucket, you have good material. We don't seem to get as good of compaction in a bucket as we do out in the lakes and ponds themselves. This is why we relax our expectations within the bucket.
I've forgotten who's website I got this from or I'd give them credit.
Rickro:
This is not an easy question to answer with do it yourself tests or even laboratory tests unless it is a no brainer with several feet of good clay. Dave is right about digging some test pits. As Ric indicates by the test method, what you are really looking for is permeability, which is related to the clay content, but also to other soil properties. Before using any test method, you will need to convince yourself that soils are relatively uniform in the area you are considering for the pond. It would only take a very small area of high permeability soil to drain a large amount of water. The best way to do this is with multiple borings or test pits.
After confirming soil types in the pond area, you have several test methods available. Ric's method will give some good qualitative information but I'll explain a few more options where a geologist or engineer could be helpful.
First, you could have lab particle size testing done, which will tell you the actual percentage of sand, silt, clay gravel, etc. (my company charges $85 each) be sure to order the "loss by wash" for the clay percentage. There is a simple calculation called Hazen's formula where you can take the particle size results and approximate the permeability.
You can also have a few laboratory permeability tests done on soil samples (more expensive $175-$300 each). These are recompacted soil tests and tend to give lower permeability results than actual soil conditions because the soil structure is not preserved. Estimates of permeabilty can be used to calculate the time it takes water to migrate through a soil.
The method I prefer is to conduct field testing on your soil using a double ring infiltrometer. This is really a fancy perc test. This involves setting two concentric rings into the soil which will form the base of your pond. The outer ring could be a drum cut in half and the inner ring a piece of 12-inch PVC. The basic idea is to fill both rings with water and measure the drop in the inner ring over time. The water level in the outer ring is maintained constant and insures that you are measuring vertical infiltration in the inner ring and not just horizontal leakage under the PVC.
Lastly, and probably the first thing to do is call your state agency and the NRCS office. They probably have pond suitability information based on soil type along with soil maps of your area. The maps are very general and you will still need some borings or pits to confirm, but depending on your soil this may be all you need to do.
This sounds like a lot of effort and it is, but if you have any questions about your soils holding water it's better to know before you sink money into constructing a pond that won't hold water.
Thanks for all the help.
Rick