Temperature underground

Does anybody know where I can look up the temperature for my area (E WA) at 6 feet (or so) down? I've been searching around for hours and haven't been able to figure this out. Thanks!

You might try checking the water temperature of springs in your area.

Estar Holmes wrote:Does anybody know where I can look up the temperature for my area (E WA) at 6 feet (or so) down? I've been searching around for hours and haven't been able to figure this out. Thanks!

Ground temp can vary with depth and soil moisture.

One of the reasons I started doing tests and  recording data at different depths.

Yes... go to https://greenhomebuilding.com/pdf/GroundTemps.pdf and there is a chart of undergroound temperatures around the world.

I'm in Newberry Springs, zip code 92365 in Southern California Mojave Desert.  Well water here from 100 -200ft deep water table runs around 70 degrees Fahrenheit.  Some wells have warmer water.  Summertime temperatures in underground cellars with only 2-3 feet of earth cover will normally be around 80-90+ degrees F.
What a revelation it was to me when temperature samples take during a soils compaction test for my earth-sheltered house, showed the migration of bands of winter coolth and summer warmth all within a depth of 4-5 feet before it averaged out.  The 54-60 degree temps I was counting on from underground house texts, just doesn't fit my soil climate.
Paul

Here in Kansas you can call the county extension office for information like that.
I would guess other states have something similar.

Temps can vary underground depending on the water table in the location you dig.

The easiest way is to dig a hole.  A standard post hole digger will get you down 4'.  If you shovel out the top you can probably get another foot deeper.  If you measure temps of the soil you're removing as you get deeper you should be able to guesstimate the 6' temp.  For instance:

6" down - 70f
1' down - 67f
2' down - 65f
3' down - 63f
4' down - 62f
5' down - 61f
6' down should be around 60f.

Check the "Near ground surface temperature map":
https://www.smu.edu/dedman/academics/departments/earth-sciences/research/geothermallab/datamaps/temperaturemaps

6 foot down the temperature of the earth will vary seasonally, around 20' down it will stabilize (close) to the average annual air temperature of your area, normally very similar to the ground water temperature:


Notice on the graphs how the temperature stabilizes and lags behind surface temperature as the depth increases and the "wave of heat" slowly travels through the earth:


(all photos found online searching "underground temperature chart")).

Something mentioned I believe by John Hait in his book "Passive Annual Heat Storage" (currently available for download on archive.org) is that rain water soaking through the ground can greatly affect the temperature underground: if you're depending on the thermal mass of the ground, or the ground temperature then he recommends creating a water impermeable layer (usually plastic sheeting/pond liner) near the surface to prevent rain from cooling the earth or moving heat out of the thermal mass.

Edit to add: Also discussed by John in his book, if you put insulation along with the water barrier, and extend that out 20' or so in all directions, you get the temperature equivalent of 20' of covering earth without having to go down that far, since the heat in effect has to go 20' to the side because of the insulation under the water barrier.