35 WorldWide Drilling Resource® Environmental Monitoring by Thomas Kwader, Ph.D., P.G. Owner, Qwater Well Developer and WorldWide Drilling Resource® Hydrogeologist When Good Wells Go Bad How long should a new well last? Wells are relatively expensive, but can supply clean potable water for tens of years or more. There are fractured rock wells (limestone, dolomite, basalt, etc.) that have supplied water for even longer periods of time while undergoing little or no maintenance. Wells built with a screen are apt to lose their capacity due to sand or other abrasive materials wearing out the impellers or clay-like materials filling the impellers and well screen as the pump ages. To determine if the diminished well yield is due to pump wear, clogged impellers, or a drop in the water table due to drought conditions or heavy pumping, it would be helpful to determine if the specific capacity of the well has declined since it was initially drilled. Specific Capacity (SpC) is the amount of water pumped in gallons per minute divided by the amount of drawdown in feet: SpC=gpm/drawdown (in feet); or SpC=gpm/dd (in feet). For example, the specific capacity of a well pumping 100 gpm with 25 feet of drawdown has a SpC of 100/25=4 gpm per foot of drawdown. If the specific capacity is declining over time, this is a sign the pump is wearing out or the water level is declining (or both). Periodic Specific Capacity data can help determine if you have a well plugging problem developing or a declining water level problem. Lowering the pump or valving the flow down may help alleviate the problem to some extent. Tom Tom Kwader may be contacted via e-mail to michele@worldwidedrillingresource.com ENV
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