A Well-Drilling (Customer's) Primer

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Speaking of casing, that part of the drilling operation is handled somewhat differently with the rotary method, too. Instead of combining the drilling and sleeving procedures as the cable driller does, a rotary rig bores a slightly oversize shaft into which the casing is later installed. Since the walls of the hole can start to collapse before the casing can be set, the operator often must pump driller's mud (bentonite clay or a synthetic equivalent) down the shaft with the flush water to firm up the sides. Once that's completed, the tapered-tip casing can be fed into the hole and either locked into bedrock with the help of an air hammer or packed with gravel. The well is then sealed with concrete to prevent surface water from leaking past the casing and contaminating the groundwater supply that feeds the well.

At this point you might be wondering which drilling method is better. Well, there's no single answer to that question, but here are some facts to mull over: A rotary rig can usually punch a hole about five times faster than its cable-driven cousin. It can also go deeper with less effort and can even cut through the hardest rock with the help of carbide-tipped bits.

The cable rig, on the other hand, makes slower progress, owing to its design ...and can have some real difficulty going beyond the 150-foot range. Too, the tool point isn't as effective on rock, so dynamite may be needed to fracture the harder material. Finally, because it's under such stress, the casing material used with a cable drill is generally heavier, stronger, and more expensive-by up to a dollar a foot-than that used in a rotarydrilled well.

In light of these facts, why would anyone want to use the cable method to drill a well? Simply because the shock of the heavy tool bit can open fissures in the rock, freeing up any water-bearing veins ...which effectively means that a cable-drilled well may not need to be quite as deep as a rotary-bored one to yield a satisfactory water flow.

GO WITH THE FLOW

Actually, your choice of a drilling method is dictated by which local contractor you hire ...and if they all use similar equipment, obviously your options are limited. Far more important in your quest to get the most for your buck are the price per foot for drilling, the cost and size of the casing, and, ultimately, the yield of the well in gallons per minute (GPM).

Unfortunately, I can't give you pricing information ...simply because the composition of the overburden varies so much from region to region. What I can tell you with some certainty is that there'll be a minimum-depth fee, usually set at 100 feet. Much of the expense of drilling is in the moving and setting of the rig, so even if the operator hits good water at 60 feet, you'll probably still be charged for a 100-foot well.

As far as casing goes, 5" and 6" internal diameter (I.D.) are both common sizes for a professionally drilled well, though 4" pipe isn't unheard of. Aside from cost (which might vary by a dollar a foot between sizes), the diameter of the casing is important because it's directly related to the well's storage capacity. If you think of your well as a long, thin reservoir of water, it's easy to fathom how a broader casing can store a greater volume than a narrow one. Just for reference, a 4" casing can hold about 2/3 gallon per foot; a 5-incher, just over a gallon; and a 6" one nearly 1-1/2 gallons.

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