I agree with Boyd. There are all different kinds of testing pipes, depending on who is doing it. Some are even pipes (tubes).
http://mywebpages.comcast.net/teegate1/IMG_5173.JPG
A description of them:
These particular pipes are part of a hydrologic
transect to understand subsurface hydraulic gradients
near streams. The locked blue well casings are protecting the more
conspicuous larger diameter wells, which are generally at the upland end of
the transects. The pipes with the electrical tape covering the ends are
less conspicuous wells.
You may see gray PVC pipes in some other areas that were installed by the
Pinelands Commission at the center of their 10m x 10m ecological study
plots to understand relations between vegetative communities and depth to
the water table
Guy