CWD CWD Well Maintenance & Rehabilitation 1 — Questions and Answers
Question 1: What is the primary purpose of well redevelopment after installation?
- Remove drilling fluid and fine particles to restore natural permeability (Correct answer)
- Increase the water table elevation
- Test for bacterial contamination
- Measure aquifer transmissivity
Correct answer: Remove drilling fluid and fine particles to restore natural permeability
Well redevelopment removes residual drilling fluids and fine particles that clog the formation, restoring the natural permeability around the well screen.
Question 2: Which surging method uses a tight-fitting piston to alternately push and pull water through the screen?
- Overpumping
- Mechanical surging with a surge block (Correct answer)
- Air surging
- Jetting
Correct answer: Mechanical surging with a surge block
Mechanical surging with a surge block uses a tight-fitting piston (surge block) that is moved up and down to force water back and forth through the well screen, dislodging fine particles.
Question 3: A well experiencing gradual decline in yield over several years most likely indicates:
- Aquifer depletion
- Pump wear only
- Biofouling or mineral encrustation of the screen (Correct answer)
- Seasonal water table fluctuation
Correct answer: Biofouling or mineral encrustation of the screen
Gradual yield decline over years is a classic sign of biofouling (iron bacteria) or mineral encrustation (calcium/manganese deposits) plugging the well screen and formation.
Question 4: What chemical is commonly used to treat iron bacteria fouling in a domestic water well?
- Sodium hypochlorite (chlorine bleach) (Correct answer)
- Hydrochloric acid
- Potassium permanganate
- Hydrogen peroxide only
Correct answer: Sodium hypochlorite (chlorine bleach)
Sodium hypochlorite (chlorine bleach) is the most common chemical used to shock-chlorinate wells to kill iron bacteria and other biological fouling organisms.
Question 5: The specific capacity of a well is defined as:
- Total gallons pumped per day
- Pumping rate divided by drawdown (Correct answer)
- Drawdown divided by pumping rate
- Static water level minus pumping water level
Correct answer: Pumping rate divided by drawdown
Specific capacity is the pumping rate (gpm) divided by the drawdown (ft), expressing how many gallons per minute the well yields per foot of drawdown.
Question 6: When rehabilitating an old well, which test should be performed BEFORE chemical treatment to establish a baseline?
- Video camera inspection
- Pumping test to measure current specific capacity
- pH test of the water
- All of the above (Correct answer)
Correct answer: All of the above
Before rehabilitation, a video inspection, pumping test for specific capacity, and water chemistry/pH testing together establish a complete baseline to measure the success of rehabilitation.
CWD CWD Well Maintenance & Rehabilitation 1
What is the primary purpose of well redevelopment after installation?