How to Test Your Soil

The soil conditions for your lot must be figured out by digging test holes where the earth loop will be installed. There is no other way to figure it out. Every horizontal loop installation must have soil samples taken or we will only be guessing what size earth loop to design. Most geothermal heat pump contractors guess, and that is one of the reasons that there is so much trouble in the industry. Since geothermal heat pumps are installed for energy (and money) saving, there cannot be any guessing about sizing and designing any part of it.

Most people these days have a video camera, so you can easily make a video while you are doing a soils test and email the video to us. People send information of their soil testing, their furnace rooms, the areas where the air ducting will be installed, their windows, and many other details of their home so we can correctly calculate their geothermal system for them.

The Test

Your earth loop designer will tell you how deep to dig your test holes. You should be able to reach a depth of about 4 or 5 feet with a pair of post-hole diggers, but if you must test deeper than this, you'll need an excavator to dig the holes for you.

Before you do any digging or testing, be sure that it has not rained for at least 24 hours, because sometimes surface water will run into the hole and then the testing results will be inaccurate.

You will need to dig test holes in each field location that it's possible to install the loops. Try to dig about the center of the area the loops will go in (your designer will tell you the approximate possible space needed for loops). If you have a large area of the field that changes from dry to wet, take samples in both places.

You must do the test as soon as the dirt is removed from the trench, or as soon as you dig your last shovel of soil out of the hole. If you have an excavator dig for you, have them dig down to the specified depth, and then have them bring up a scoop of dirt for you to test. NEVER GET DOWN INTO AN EXCAVATED TRENCH THAT IS MORE THAN 4-FEET DEEP BECAUSE IT MAY CAVE IN ON YOU AND KILL YOU.

Have someone take a video of you doing all the tests. Be sure to say where the test hole was dug as you start the test (as in front yard, back yard, side yard, top of the hill, bottom of the hill, etc.). Try to have the camera close enough to your hands that the soil is in good focus and easy to see.

Dig down to your required depth, and immediately bring up a shovel of soil. Take a handful of soil and close your fist on it tight. Then open your fist so I can see if the soil packs in your hand. Next take a pen or something like it and see how far the pen will push into the soil before it falls apart. Do this test 3 times in a row, pulling a new sample of soil out of the excavator bucket for each test.

If the soil will hold together in your hand at all, do the next test: with two hands, try to roll the soil into a "snake" like a child would do with modeling clay. If it will roll, and hold together, bend the snake til it doubles back on itself slowly, so I can see if the bend cracks or not. Do this a few times in a row.

Last, wait 1 hour and look into the hole. If you see any water standing in it after the hour, it means the soil is saturated, and that is the best we can hope for. You won't have to bring any more soil out of the hole; just tell us where the hole is and that you saw water in it.

Here's an example of what a good soil test video might look like.

Or you can send us the soil samples

If you don't have a video camera, or you'd rather not do the tests yourself, you can send your soil samples to us and we will analyze them. Dig the test holes, and have freezer bags ready. Once you are at the test hole depth take about 2 cups of soil and put it into a freezer bag, and triple bag it. Try to push out as much air as you can. Mark the bags "First Test Sample" and whether it's from the front or back yard (or wherever it's from).

Wait 1 hour and see if there is any water in the holes. Take a photo or make a note to email or text to us of whether there is water or not, and then box up the soil sample bags to send to us.