I got to this site while looking for data on subsurface temps in Honolulu, where I am pondering a cut & cover earth-shelter (see the subject Appendix 1 at www.greenbuildingtalk.com/desktopmodules/ntforums/viewer.aspx?portalid=0&moduleid=369&attachid=272 )

I don't know from where on this site that page might be linked, but I assume it might have been from this geo-related forum...right?  It's a list by local of, well, "ground temperatures," if one is supposed to take the title literally.  No depths given, no seasons, etc.  (also has "Application Guide AG 31-008" at the bottom).  OK, Honolulu is warm, as everyone knows, but what is meant by a "ground temperature" of 79F?

Maybe this extensive table has some other purpose.  At any rate, I am looking for temp ranges in Honolulu for up to about 30' below grade.  Anyone?

Mahalo,

Dave

The figures are correct. The 50 degree average water temperature you expect for most of the United States come from the weather being 90 to 100 degrees during the summer and 20 to 30 degrees in the winter the average between the two gives you your ground temperature. The ground is like a sponge, that slowly soaks up the heat from the sun, if there is no cold weather the earth doesn't have time to bleed off the heat it absorbed when it was hot, thus you have higher ground tempertures. I'm not sure how far down the earth is heated by the sun, I think if the earth's crust is thick enough, you could dig down deep enough to give you colder temperatures, but were talking thousands of feet there, and at some point the earth will become hot again as you dig closer to the molten core. Being that Hawaii was formed with volcanic activity, I wouldn't want to dig too deep in the surface, otherwise you could be the proud new owner of a brand new volcano. :)

In short the answer is yes, the figures are correct from 5 to 500 feet below the surface. 

  

Deep ground temps are specified for depths below 30'. Five feet is too shallow - earth at that depth is subject to seasonal variation