Drilling General Exam: Sanitary Well Design, Grouting, and Completion
The general drilling exam is the part every CWD candidate takes, whatever specialty is added to it. It tests whether you can site, design, construct, develop, and test a well that keeps contamination out of the aquifer and sand out of the pump. Expect groundwater fundamentals - aquifer type, static versus pumping level, cone of depression - alongside casing and screen selection, annular sealing, disinfection, yield testing, and the state well-construction code that overrides any rule of thumb.
Core rules that carry marks
- Seal the annulus from the bottom of the casing upward with a tremie pipe; top-down pouring bridges and leaves voids.
- Casing terminates above finished grade, is capped and vented, and the pitless adapter sits below the frost line. No buried suction line, no direct sewer connection, no cross-connection at the wellhead.
- Size the screen slot or gravel pack to the formation - retain the formation, pass the water - then develop until sand and turbidity stabilize.
- Disinfect with a chlorine solution at the concentration and contact time your code sets (commonly 100 ppm for 12 to 24 hours), then pump to waste until the residual clears.
Worked example. You grout a 10-inch hole around 6-inch OD casing to 100 ft. Annular area = π/4 × (0.833² − 0.50²) = 0.349 ft²; volume = 0.349 × 100 = 34.9 ft³. Neat cement yields about 1.2 ft³ per 94-lb sack, so 34.9 ÷ 1.2 ≈ 29 sacks; add 10% for washouts and overbreak and order 32 sacks, with roughly 5.2 gal of mix water per sack. Convert inches to feet before anything else - that single step is where most candidates lose the mark.
Traps
Using full hole volume instead of annular volume. Computing drawdown from the wrong datum - it is pumping level minus static level, both read from the same reference. Treating specific capacity (gpm per foot of drawdown) as constant at large drawdown. Quoting a national figure when the state code is stricter.