The whys

The whys

The common reasons why a well to be drilled might need cementing can be listed and described as follows:

• First, every well should be cased to a point below the level of possible contamination. In gravel and sand it is desirable to cement the well casing down to a point as close as possible to the top of the screen, or at least to the lowest possible pumping level. If you have impervious strata above the producing gravel or sand, the cement grout should extend from the surface down to the impervious barrier. The use of cement grout in such cases is superior to backfilling around the casing with drill cuttings or clay.

• Second, on a well producing from consolidated rock directly below "till" or "drift" formation, the surface formation above the producing formation may be too thin or too porous, in which case the surface pipe driven into the rock is not sufficient protection against surface pollution. A driller must drill a sufficient depth into the consolidated rock, and below the zone of pollution and, there, install a permanent line of casing. The proven, safe way is to completely fill the annular space between the surface pipe, the drilled hole, and the permanent interline of casing with cement grout.

• Third, quite often, we must deal with manmade cases of pollution. Man-made quarries, filled with debris and garbage, septic tanks, and leaching fields, drainage wells, abandoned unplugged wells, nitrogen derivatives from modern fertilizers, are just a few possible contributors to pollution of a well to be drilled. Therefore, to make a well capable of producing potable drinking water, it is generally necessary to double-case a well and, at the same time, cement a liner well down into the producing aquifer and down below the possible pumping level.

• Fourth, it is often necessary to case-out an entire undesirable aquifer and to go to a lower formation for better quality water or for water less liable to be contaminated. Again, it is a situation requiring a cemented casing. Older wells often were cased with a packer at the bottom of the liner, and often, there was no real shut off. But if a seal was perfected, it was only as good as the casing which would be attacked by corrosion on the outside as well as the inside. The result usually was a leaky casing in a short time and a well repair job.

• Fifth, more and more attention is being given to the proper plugging of abandoned wells. Procedures have been established by state and local authorities and cementing has been an accepted practice.

• Sixth, usually the only repair work necessary on small-home wells is where the contact of the casing and rock has failed, or when a hole develops in the surface pipe. This generally calls for a liner extending below the original surface pipe and, here again, the safe procedure is to cement the annular space from top to bottom.

• Seventh, in drilling with a rotary machine, an open hole can be drilled down into bed rock, and the surface pipe installed in the open hole. When this is done, the annular space should be cemented.

The above list, of course, is not complete, but covers the common cementing jobs. The work can be done with rather simple equipment and a little ingenuity.