Well Development, Testing, and Disinfection
What this domain tests
This domain tests what happens after drilling: removing drilling fines, measuring yield and drawdown, and disinfecting the well before it is placed in service.
Development and testing
- Development removes mud, silt, and fines from the screen and filter pack. Common methods are surging, bailing, air-lift pumping, jetting, and overpumping. Develop until the water is sand-free and clear.
- A yield test pumps the well at a controlled rate and measures drawdown until it stabilizes. Static water level is measured before pumping; pumping water level is measured during pumping. Drawdown is the difference.
- Specific capacity = pumping rate ÷ drawdown, in gpm per foot. It compares well performance and estimates drawdown at another rate.
Worked example
Static level is 60 ft; after pumping at 12 gpm the level stabilizes at 40 ft. Drawdown is 60 − 40 = 20 ft. Specific capacity is 12 ÷ 20 = 0.6 gpm/ft. At 8 gpm, expected drawdown is about 8 ÷ 0.6 = 13.3 ft. Reasoning: specific capacity assumes a roughly linear relationship within the tested range; it is an estimate, not a guarantee.
Disinfection
New and repaired wells are disinfected with a chlorine solution, held for the required contact time, then flushed and sampled for coliform bacteria. Do not sample before the chlorine is flushed out, or the residual will mask or invalidate the result.
Traps that cost marks
Testing before development is complete; subtracting the levels in the wrong order; confusing yield with specific capacity; and sampling disinfected water without flushing.