Why a sand water filter may not remove sand from your water system
Conventional well theory holds that water enters the well evenly across the length of screened or open borehole. It has always been assumed that a well with 100 feet of water producing length, and a 1,000-gpm pump will. uniformly produce 10 gallons of water per foot of producing zone. However, it has been clearly demonstrated that this is not what really occurs.
What actually happens is that pump suction energy is distributed very unevenly in the well. This results in water entering the well at very high velocities near the pump, and being virtually stagnant at the farthest points from the pump. Water rushes into the well near the pump to satisfy the pump demand. Once this water reaches turbulent velocity, no additional water flow occurs at that point, and the suction energy is pushed farther down in the well. This process will continue until all of the pump suction energy is dissipated or the pump breaks suction and begins to pump air. Thus it can be seen that most of the water is produced in only part of the well.
In many cases, 100% of the water is pulled from a third or even less of the available producing zone. The result of this uneven energy distribution is mineral encrustation and sand production as described above. These preventable problems will certainly cause deterioration in well performance, and can often lead to premature failure of the well.
Typical approaches to these problems can fairly be described as "treating the symptom" rather than correcting the underlying cause of the problem. These treatments include periodic removal and replacement of the pump, repeated attempts to rehabilitate the well through various chemical and mechanical methods, re-screening or lining the well, the use of settling tanks, sand separators and/or filtering systems. In the worst cases, wells are replaced and then the cycle repeats itself.
Common Causes of Well Deterioration
Well deterioration can be caused by: 1) Mineral encrustation, 2) Sand production and/or 3) Biofouling. In all three cases, well deterioration occurs both to the well screen and casing as well as to the surrounding formation itself.