All water wells are prone to a decrease in the quantity or quality of the water produced over time. This is usually due to a combination of biological and chemical action. It is estimated that biofilm is responsible for at least 80 percent of well clogging. Biofilm is the slime or polysaccharide polymer that surrounds and protects live bacteria. Chemical and galvanic corrosion and encrustation (scale) are additional factors.
It is more effective to rehabilitate a well before it has lost a significant amount of its original capacity. Biofilms and scale are easier to remove when they are young and soft, rather than when they are old and hard.
If you own or operate a water well, keep good records of its performance and specific capacity. Specific capacity is the discharge of the well (typically gallons per minute) divided by the drawdown in the well (the difference between the pump-off water level and the pump-on water level). Use a flow meter (or a bucket and stop watch for a small well) to measure the discharge. Use an electric sounder or a tape to measure the non-pumping and pumping water levels at least quarterly.
In the past, water well rehabilitation consisted of mechanical brushing combined with the addition of readily-available acids to dissolve the expected mineral encrustation.
Current practice recognizes a variety of possible causes for diminished well performance.
The following methods can be used to diagnose well fouling and to define specific methods of rehabilitation:
Document the well construction
Evaluate the change in well yield or specific capacity over time
Evaluate the change in water quality over time
Document prior rehabilitation treatment
Sample the well water (at different depths, both static and pumping) and scale deposits for biological and chemical analyses
Video log the well casing and screen
Pump test the well to establish a baseline prior to treatment
In addition to mechanical brushing and agitation, well rehabilitation can include the use of mineral acids, organic acids, caustics, polymer dispersants, surfactants, and chlorine disinfectants.