Vance,
A while back, if you recall, I called you with a small problem. I had a client that wanted to install 20 temporary piezometers. I was going to install the piezometers at 20 ft. with 5 ft. of screen, sand 1 ft. above the screen, and pour granular bentonite to the surface, hydratingas we go. The client was then going to come behind me and do his own sampling of the wells. I was then, after installing the 20 wells, to come back to the first well and start to P&A the wells that had been sampled.
My problem was I wanted to figure a way to grout the holes without having to pull the wells and go back down with tremmie pipe to grout. The ground water level was at about 7 ft. and the client was worried we would have problems jetting the tremmie all the way to the bottom. One solution to this problem would be to push grout rods to the bottom and grout to the surface. This, however, is time consuming and the client had a limited budget.
As you may recall, I called you to see if you made some kind of bottom plug that would blow out under the pressure of the grout, allowing us after sampling the wells to then use the one inch wells as a tremmie pipe to grout as we pulled the wells.
I had called several manufacturers and no one came up with a possible solution. However, during our discussion of the problem we came up with the possibility of using a by-product of your prepacked bentonite risers, which consisted of 1-1/4 x 3" cylinder-shaped polyurethane foam plugs.
To test this theory, we installed the first 6 wells, three the conventional way pushing 3-1/4" casing to 20 ft., dropping in a one inch piezometer with screw-on bottom cap, 5 ft. screen, and 3 and one half 5 ft. risers. We poured sand down the casing as we pulled out the casing, bringing the sand one foot above the screen. Then we poured granular bentonite through the casing as we pulled the casing to the surface. We then installed the next three wells using the same procedure except instead of the screw-on bottom plug we stuffed the polyurethane plug in the bottom. The plug fit snug enough to stay in place.
These first 6 wells were all in the same area and after sampling the wells they came out with approximately the same amount of turbidity. The client was satisfied with the new procedure and we were able to save a lot of time, which in turn saved the client money and allowed him to stay within his budget.
Thanks for your help. I was happy that between the two of us we were able to solve the problem, as well as come up with a procedure that may help in the future.
Mark Decker
Fugro Geosciences
