Well Drilling Practices
The Well Drilling Practices domain tests whether you can pick a method that fits the ground, carry the hole to bedrock without losing it, develop the well so it produces sand-free water, and document the result. Connecticut jobs are usually glacial overburden over crystalline bedrock, so most items involve casing through running sand or till and finishing a fractured-rock well.
Match the method to the geology
- Mud rotary for unconsolidated sand, gravel and mixed till where the borehole must be held open; the filter cake supports the wall and the mud lifts cuttings.
- Air rotary or down-the-hole hammer for hard bedrock, where returns come back as dust and chips.
- Hollow-stem auger for shallow cohesive soils and monitoring wells.
- Casing advance (drive-and-wash) where sand flows in faster than you can drill.
Casing, seal, development
Casing must pass through all unconsolidated material and seat at least 5 ft into competent rock, with the annulus grouted from the shoe to the surface. Develop by surging, air lifting or jetting until the discharge runs clear and sand content has stabilized; overpumping a new well can drive fines into the fractures you are trying to clean.
Records and yield
Record the static level after recovery, pump at a constant rate, and note the pumping level at set intervals. Log samples every 5 ft or at each formation change, plus water strikes, casing and grout depths, and yield.
Worked example
Overburden is 38 ft thick and the driller wants a 6 ft rock seat. Casing length = 38 + 6 = 44 ft. The hole is 10 in. and the casing 6 in., so annular volume per foot is (10 squared minus 6 squared) divided by 144 = 0.444 cubic ft per ft; total = 44 x 0.444 = 19.5 cubic ft. Neat cement yields about 1.15 cubic ft per 94-lb sack, so 19.5 / 1.15 is roughly 17 sacks, placed by tremie from the shoe upward.
Traps that cost marks
- Grouting from the top down, which channels and leaves voids behind the casing.
- Seating casing only a foot or two into rock, so the seal sits in overburden.
- Reporting drilled depth as if it were available drawdown.
- Skipping water-strike depths, which the completion report and pump setting both depend on.