Well Development, Testing, and Disinfection
What this domain tests
Development, testing, and disinfection questions ask whether a completed well is efficient, sand-free, and biologically safe. Content includes development methods and stopping criteria, drawdown and specific-capacity testing, and the chlorination and sampling sequence.
Development
- Development removes drilling fluid, mud cake, and fines from the screen and filter pack and consolidates the pack around the screen.
- Methods include surge blocking, bailing, air lift, high-velocity water jetting, brushing, and controlled overpumping. Aggressive surging in a weak formation can collapse the pack, so match the method to the geology.
- Stop when the water runs sand-free and yield and drawdown have stabilized; further work then buys nothing.
Testing
- Record the static water level before pumping, run a step-drawdown test at increasing rates, then a constant-rate test long enough to show stabilization (a few hours for a domestic well, longer for higher-capacity wells), plus a recovery reading.
- Specific capacity equals pumping rate divided by drawdown. Compare it across steps: a specific capacity that falls as the rate rises signals well loss or turbulence.
Disinfection
- New, repaired, or redeveloped wells get shock chlorination: a dose strong enough to give about 100 mg/L free chlorine throughout the water column, with at least 12 hours contact, and 24 hours commonly used, then pumped to waste.
- Dechlorinate before discharging to a storm drain or waterway; chlorinated water is a pollutant.
- Sample for total coliform and E. coli only after the chlorine has dissipated, using a bottle containing thiosulfate. Sampling a still-chlorinated well gives a falsely clean result.
Worked example
Static level 40 feet. At 30 gpm the pumping level is 60 feet, so drawdown is 20 feet and specific capacity is 1.5 gpm per foot. At 45 gpm the level is 75 feet, so drawdown is 35 feet and specific capacity is 1.29 gpm per foot. Falling specific capacity means the extra rate comes at disproportionate cost: the well has significant well loss, and the right follow-up is a proper step test rather than more pumping.
Traps that cost marks
- Testing before development is finished, so results reflect mud rather than the aquifer.
- Reporting a yield figure from a short test with no stabilized drawdown.
- Collecting the bacteriological sample while chlorine residual remains.