Monday, November 12, 2018

Life Expectancy of a Water Well

How long a well lasts depends on many factors; the geology and hydrology of the region, the amount of ground cover nearby, how the well was constructed, what equipment has been installed “down hole,” and what maintenance activities have been performed to date.

Prince William County first implemented county wide well construction regulations in 1970’s. Those regulations were very progressive for their time and quite similar to the current state wide regulation implemented in 1992 and still in effect today. When a well is drilled the well driller must fill out the “Water Well Completion Report.” This report is chock full of information about the well. Some of the information is : location, type and class of well, the well depth and diameter, the depth to bedrock, and total depth of casing, the presence and size of screen and or mesh, the location of water zones, the static water level (unpumped level measured) and the stabilized yield. The only water sampling that takes place under regulation is a coliform bacteria test after the well has been disinfected and the residual chlorine has dissipated.

As a water well ages, the rate at which water may be pumped referred to above as the well yield tends to decrease. The mechanical components and the well structure, screens and casing all age and deteriorate. Well maintenance and monitoring of the water and well’s performance is important in keeping the water flowing. A well owner must think about their well in terms of stewardship over the long term, long before your well fails.

To ensure water quality, well water should be tested annually for total coliform bacteria and E. coli bacteria by an accredited testing laboratory (states keep lists of accredited labs). Water wells should also be inspected annually for obvious signs of damage or contamination. Be sure the area within 100 feet around the well is clear of debris or items that might pollute the water supply. In addition, wells should have their static water level, pumping water level and flow rate tested and recorded when the well is new, and tracked occasionally over the years. Establishing benchmarks, for static and pumping water levels, flow rate, and specific capacity, is critical for tracking well performance and will help identify trouble long in advance of well failure. In most cases, the well owner will have several years to react to problems that are manifesting in the well and possibly take remedial action before it’s too late.

A well can last 50 years (I know of one well that did). However, a drop or complete loss of water production from a well can sometimes occur even in relatively young wells due to a lowered water level from persistent drought, nearby development, or over-pumping of the well which can dewater the water-bearing zones. More often, the fall in well yield over time can be caused by changes in the water well itself. According Penn State Extension these changes can include:
  • Encrustation by mineral deposits 
  • Bio-fouling by the growth of microorganisms 
  • Physical plugging of groundwater aquifer by sediment 
  • Well screen or casing corrosion 
  • Pump damage 
Monitoring of a well’s performance brings everything into view, good or bad, and should a well owner go for decades without major trouble, at monitoring over the years can give you peace of mind. Monitoring can prevent being surprised by well failure when, in a panic, patchwork or inappropriate work is done. Often the money spent on patchwork by the well owner is lost. Monitoring of the well’s performance allows for preventive maintenance.

Generally, a decrease of 25% or more in well yield indicates that rehabilitation of the well is needed. Delaying rehabilitation can significantly increase costs and in some cases make rehabilitation impossible. Measures taken to correct these problems are referred to as well rehabilitation or restoration. A successful well rehabilitation will maximize the flow of water from the well. The chances for successful rehabilitation are dependent on the cause or causes of poor well performance and the degree to which the problem has progressed.

The two most common methods to rehabilitate a water well are:
  • chemicals to dissolve the encrusting materials from the well 
  • physically cleaning the well 
Encrustation caused by mineral buildup or by bio-fouling are common causes of well failure. Encrustations are mineral deposits which buildup on well screens and in the rock fractures or openings that deliver water to the well. Mineral buildup is caused by minerals that fall out of solution depositing on the well screens and well fractures. The primary cause of bio-fouling, or biological clogging, of well screens and rock fractures is attributed to iron bacteria. These and other similar bacteria create a slimy bio-film. Avoiding this is why I regularly chlorine treat my well.

The usual methods for rehabilitation of chemical encrustation involves the use of strong acid solutions to dissolve encrusting materials combined with physical methods that include using a brush attached to a drilling rig, high pressure jetting, hydro fracturing of the well (hydrofracking), and well surging.

A portion of the loss in well performance over time can be caused by the accumulation of fine particles from the aquifer in the borehole and clogging the well screen. These particles can also cause pump damage, and result in short lifespan of replacement pumps. It may be necessary to replace the well screen or protect the pump. The most important preventative measure to avoid sediment from plugging a well is proper well development, as required by modern well regulations. A well developed and healthy well should not require a sediment filter.

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