Too many variables to say for sure. It depends on the the nature of its host, be it water, desert sand, or farm land, maybe. We did that way back when, to preserve milk till the creamery truck came came out and picked up our product. We cooled the milk first with a ring of spray on the neck of 20 gallon cans, and then set them down into a cinder block pit to maintain the achieved cooling. But that was in the 40’s and 50’s when lots of people really worked for a living. The truck was irregular and sometimes came 4 hours after milking in a time when farmers did not have phones at all, and hardly 10 % could afford such luxury.
In your case, you should consider 2 pipes, well spaced and with an electric computer fan in one of them.
the general earth temperature about 20 feet down is a constant 69 degrees year round. at 8 feet, there’ll be some shift of that toward the surface temperature, but i think it would only amount to about 5 degrees