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WELL FAILURE: Possible Causes Other than Drought
"UNDERSTANDING MICROBIAL AND MINERALOGICAL PLUGGING "
Scott Mundell, 10/31/2007
When we think of water, we think of turning on the faucet. If water doesnt flow, we assume the well pump is bad and call a pump or drilling contractor. Sometimes, however, the problem isnt with the pump. The recent drought and reports of numerous well failures reminds us that we need to pay more attention to our wells.
Wells need maintenance, too. You dont continually operate your car without checking the fluid levels or changing the oil. Ignoring maintenance will shorten your cars lifespan. The same holds true for your well. Ignoring your well could result in increased bio-fouling, mineral deposition, and loss of well capacity. Lower yielding wells and wells with shallow water-bearing zones are especially vulnerable if their pumping rate exceeds their recharge rate.
The primary loss of well capacity is the loss of its static (non-pumping) water level. If you experience loss of capacity in your well, you must first compare its static water level with its original static water level. Detailed records must be maintained (seasonal static water levels, seasonal pumping water levels, well yield, and a good well log with depth to water-bearing zones). The loss of capacity may be due, in part, to dewatering of the aquifer and there is no immediate way to return it to its original capacity. This is particularly true during times of drought. If your static water level is normal or significantly above its water-bearing zone, the loss of well capacity may be attributed to bacteria fouling or mineral deposition caused by microbial processes.
Just as water gives life, it is also alive with thousands of indigenous populations of bacteria, with depth having no influence on the number of bacteria. There are just as many bacteria at depths of thousands of feet as there are at one hundred feet. Higher bacteria numbers are found right at the surface of the watertable where there is more oxygen, and in places such as fractures in bedrock where there is higher water mobility. These higher transmissive zones have two to four times the number of bacteria than low permeability zones due to their ability to carry organic and inorganic nutrients (elements of life) on which the bacteria are dependent.
In the absence of oxygen, these indigenous bacteria utilize oxides of minerals such as nitrate, carbon dioxide, and sulfate to breathe. These oxides only amount to about 10% of the respiratory potential that oxygen can provide, which is why oxygen is by far the most significant stimulator of microbial growth in wells and pumping systems. Over-pumping and allowing water to cascade into the well will aerate the entire water column, but anything done to enhance oxygen into the well can significantly enhance microbial growth and mineral deposition which can result in formation plugging.
Whenever there is a water environment and a surface within that environment, there is a potential for bacterial growth. The introduction of oxygen amplifies bacterial growth and microbial deposition. Most (90%) of bacteria attach themselves to well and piping surfaces as biofilms. Augmented accumulation of biofilms can increase their potential to break loose which can also account for bacterial, turbidity, taste, and odor problems.
There are many options available today to rehabilitate fouled wells. The trick is to recognize potential problems early before serious problems arise. Sometimes a simple change in well use or adding storage can inhibit cascading water problems. A good well cleaning can eliminate taste, odor, and bacterial quality problems. The benefits of rehabilitation include restoring lost capacity, decreasing drawdown, extending well life, solving water quality problems, and obtaining safe bacteriological samples. The longevity of the well rehabilitation is dependent on the extent of fouling, and as such, it is important to try to remove 100% of the fouling mass. If only 50% is removed, the well will foul again in a much shorter time. More aggressive rehabilitation methods are needed to better remove the fouling mass if fouling extends several feet into the water-bearing zones.
If you have any questions about your well or recent well problems, please do not hesitate to contact our professional staff.
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18 Nov 2013
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