New Wells drilled into bedrock are started by drilling a hole at least 18 feet deep and five feet into unweathered, uncreviced rock.  This upper hole will contain the casing; it is drilled to a diameter four inches greater than the diameter of the casing to be used.  Six inch steel pipe, 1/4 inch thick, in 20 foot lengths, is typically used for residential well casing.

The casing provides structural stability, eliminates turbidity (color) which occurs when water contacts silty or unstable earth, prevents contaminants from reaching the uncased portion of the well, and prevents surface waters from mixing with deeper groundwater sources.  The minimum casing depth is determined by state code, but the final depth is a judgment made by the driller to accomplish these objectives.

Often, a round thick piece of steel, called a drive shoe is welded to the bottom of the casing.  This allows the casing to be hammered into the bedrock while protecting its bottom edge from damage, and helps the casing achieve it's purpose.

After the casing is installed, the space between it and the hole is backfilled with an impermeable grout, either bentonite or cement, to prevent surface contaminants from traveling down alongside the casing into the lower section of the well.

The hole below the casing is continued until the owner decides to stop drilling.  If an adequate supply of water has been found and if the bedrock below the casing is unstable, installation of a liner (usually 4" PVC pipe) may be necessary to prevent cave-ins and protect the pump; otherwise, the borehole is left "open" (unlined).  Liner pipe is supported by the bottom of the well; it is not permanently attached to the ground and can be removed if the well has to be deepened in the future.

Deepening may require removal of any structure, fence, tree, power line, etc. that would prevent the drilling machine from getting centered and level over the well. The pump and liner, if any, must be removed; the casing and casing seal are left undisturbed. Next, the bit and drill rods are lowered to the bottom. There may be debris or compacted sediments to drill out before the bottom can be reached. 

At the bottom, the yield is tested to establish a benchmark, and the well is drilled deeper as needed. If a liner has been removed, it is repaired for re-use and installed. Depending on the amount and pressure of the new water that is found, it may be necessary to lower the setting of the existing pump or acquire a new pump to match the new water conditions. 

Occasionally, deepening is not feasible. Most often it is because the well is too close to a building or storage tank, because a liner is stuck, or because a pump or other steel object has been lost in the hole. Infrequently, the well bore may be too crooked, or its diameter may be too small to proceed on a cost effective basis.

In Oregon, a hand dug well may not be deepened by drilling methods.