Soil Moisture Sensor

I just got a interesting request. I have a customer that is wanting to detect how much moisture there is in the soil around a Pipeline. I have never used a moisture sensor before and most of what I find is for home use and hobbyist. I am not seeing anything that I think would handle being buried 6ft under the ground.

Has anyone here done anything like this?

Give me your ideas I can use all I can get.

I used these once but we only installed them. Not sure how well they worked.

https://envcoglobal.com/catalog/agr...g/dedicated-soil-moisture-measurement/mas-1-4

Putting "4-20mA" in the Google search weeds out a lot of the hobby stuff

Thanks Saffa,
This looks like what I am looking for!!