Forecasting Well Problems Through Data Collection
A water supply well requires regular checks and maintenance to function at optimum efficiency and prolong its life. NHDES recommends that a water supply operator regularly measure and keep the following records:
- The static (stabilized non-pumping) water level.
- Relatively stabilized pumping water level and pump ing rate in each water supply well.
- Static water levels in any nearby monitoring wells.
- Daily production volumes and pump run times. (Run time meters cost as little as $25 and an hour of an electrician’s time to install.)
Neglecting to collect this information is similar to driving your vehicle without conducting regular safety inspections or without operational warning lights. Without this information, the production capacity of the well may be exceeded or the pump may be on the brink of failure unbeknownst to the water system operator.
If a water system operator collects this information and finds that the yield or water level in a well is declining, it is important to determine whether this is a result of any of the following:
- Lower yield and/or increasing drawdown, meaning the specific capacity of the well is declining due to:
- Low recharge.
- Clogging of the well screens, aquifer pores, of borehole fractures.
- Increased water withdrawals from the well itself or from nearby water users.
- Lower yield and a corresponding decrease in drawdown, could mean the performance of the pump and associated piping may be decreasing.
- A lower static water level could be caused by:
- Reduced rainfall and aquifer recharge.
- An increase in water use in the aquifer.
- Well interference from other water wells.
In order to avoid entanglement of water level monitoring probes with wires and materials in a well, it is recommended that a stilling tube be installed in the well. State regulations require that a stilling tube be installed in all new community water supply wells and in any existing (older) community water supply well at the time its pump is serviced.
In some instances, small community water systems have experienced relatively minor leaks of less than two gallons a minute. While a leak of this magnitude is often considered small by industry standards, it can increase the daily extraction volume of a well for a small water system by over 20%. Depending on the sustainable yield of the well, even a small water leak could cause daily extraction volumes to increase over time and cause the well to dewater due to increased use. When a water supply shows a decrease in specific capacity, but the static water levels in the aquifer do not decrease, it is likely that the well screen, aquifer pore spaces, or fractures are clogged with fine sediments, chemical precipitates, or a bacterial mat.
Well drillers licensed in New Hampshire can be contracted to rehabilitate the well using a variety of treatment methods. Various drillers use different approaches to rehabilitating a well. Some drillers attempt to specifically diagnose the clogging problem and design the optimal rehabilitation treatment remedy. Other drillers will attempt to rehabilitate the well using a treatment course that they have found to be generally successful in other similar settings without comprehensively diagnosing the problem. A water system operator must assess the cost-benefit analysis of how to proceed with well rehabilitation. It is recommended that an operator obtain multiple written proposals, quotes, and references from prospective contractors that may rehabilitate their well. NHDES maintains a file of historic well development documents. If a water system is missing its original well development records, NHDES can review a water system’s records to determine what information is available. For more information, contact Shelley Frost at shelley.frost@des.nh.gov or (603) 271-2949.