Thaw probe design

Introduction

WERC uses thaw probes to measure active layer depth in summer / fall and sometimes snow depth in winter. The directions that follow are pretty much the current procedure.

Parts

Search Ben Meadows.com for Tile probe, which is the general industry name of the probe. http://www.benmeadows.com/search/tile+probe

Any of those are probably fine. I have purchased both the metal one and the Nupla fiberglass one. One thing to watch for on the metal one is that I've had the tip fall off but either are probably fine. Of the two I prefer the fiberglass model. So that's the probe but there aren't any graduations on it until it is paired with something like this tape: "Adhesive-Backed Paper Tape Scale Left to Right, mm grads, 20M, Yellow. Part number 1937A22 http://www.mcmaster.com/#

Then you also need a package of epoxy that you can get from Home Depot, Lowe's or almost any hardware store. The two compounds harden in 5 minutes type of epoxy. If you buy a couple of those then you're set. For example: http://www.amazon.com/Permatex-84101-PermaPoxy-General-Purpose/dp/B000ALJ4NS/ref=sr_1_2?ie=UTF8&s=automotive&qid=1276807051&sr=8-2

The thaw probe manufacturing procedure follows:

1) Run the tape from the tip of the probe up to the handle carefully sticking it in place trying to minimize wrinkles and such. The more wrinkles the easier it will be for the tape to be scraped off when it's going into the ground.

2) tear off the tip tape back to behind the thaw probe point so that all of the tape is on cylindrical part of the probe.

3) mix the epoxy and use your hand (in a nitrile glove) to evenly spread it over the length of the probe. You should have the epoxy go around the whole probe but thickest over the tape to protect it from the mineral soil

4) allow the epoxy to dry and apply at least a second coat, perhaps third for longevity.

If you do all that, even though it's a bit of work, you should have a probe that lasts at least a year. Redoing the tape every so often is kind of the nature of the beast but this system has worked well for us. I think I last did this maybe in 2006 and although the probes have the tape rubbed off towards the tip the 40 cm and higher measurements are still pretty visible and we've probably probed several hundred times since the tape was epoxied.