Well production can drop off over time due to blockage of well casings, well screens and the adjacent water-bearing formations. These blockages or incrustations take the form of biological, chemical and /or mechanical plugging.
The well owner should keep good records of specific capacity performance so that any decline will be immediately detected. The specific capacity is the pumping rate of the well in gallons per minute divided by the total drawdown in feet, the drawdown being the difference between the static water level and the pumping water level. The new specific capacity readings taken at various times can be compared against the original specific capacity when the well was new or redeveloped. (Note: Small variations of specific capacity can be attributed to pump and bowl wear or changes in dynamic head during the testing).
Biological Incrustation occurs when wells are populated with one of several genera of iron related bacteria. These organisms form a slimy gelatinous matrix of polysaccharide polymer material that enhances the attachment to the surface, nutrient capture and protection of the cells. They feed off dissolved iron in the water that is ultimately deposited in the form of a hydroxide. The organic slime matrix combined with iron deposits can greatly reduce pumping capacity of a well in a short period of time.
Chemical Incrustation occurs when mineral scale forms around the well bore when the well is pumped. The draw down created by pumping the well causes a reduced pressure in the aquifer, which releases carbon dioxide gas (CO2), from the water. This CO2 deficiency causes a chemical imbalance forcing dissolved minerals in the water like calcium, and magnesium to form insoluble scale. In a lesser degree, iron, manganese and sulfates may also precipitate.
Mechanical Incrustation describes the plugging which occurs when silt and clay size particles in the aquifer move toward the well during pumping or describes the poor development of a well when new. This form of incrustation is rare but can occur where large amounts of these minute particles are found.
Conclusion: No mater what problem causes the yield of the well to decline, the cleaning process is always easier if the problem is diagnosed and treated early. We know from experience that well maintenance is too often performed as an emergency procedure when the well production has dropped to 50% of original pumping rates. We take a proactive approach of regular maintenance on wells before pumping rates drop more than 10-15%. We can diagnose the problem and provide the expertise and chemicals to restore a well back to near capacity.