Module 7 — Troubleshooting Water Well Problems
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Mineral Incrustation
Mineral incrustation is a common problem in some shallow water table type aquifers
where there is an abundance of dissolved minerals including calcium, magnesium and iron,
as well as iron bacteria. When water is pumped from the well, changes in pressure and
temperature occur. This creates ideal conditions for minerals to precipitate or settle out,
causing scale formation on the casing, liner and screens.
A combination of good preventive maintenance and good management practices can
minimize the effect of incrustation. Management practices that reduce water pumping rates
can reduce the effects of mineral incrustation. A strategy of reduced pumping rate with longer
pumping intervals helps prevent incrustation of screens and perforated liners.
Biofouling
Installing and pumping a well increases the level of oxygen and nutrients in the well and
in the surrounding aquifer. Bacteria, such as iron bacteria, may thrive under these conditions.
They can form a gel-like slime or biofilm that captures chemicals, minerals and other particles
such as sand, clays and silts. Minerals, such as iron, oxidize and get trapped in the biofilm.
"
Biofouling" occurs where biofilm accumulations are sufficient to reduce water flow. This can
mean reduced well yield and water quality.
Corrosion
Chemical substances found in water can eat away or corrode metal well casings. To avoid
corrosion, the licensed water well contractor must choose a casing material that is suitable for
the water supply. For example, licensed water well contractors usually select plastic casing
liners and stainless steel well screens for corrosive water. Sulfate-reducing bacteria can also
cause corrosion. Shock chlorination can keep these bacteria in check.
Although incrustation or scale formation
occurs mostly in the screen or slotted
casing, it can also affect the formation
around the well.
Shock chlorination is effective as a
regular maintenance technique to kill
bacteria and limit its ability to create
biofilm. However, shock chlorination is not
effective at penetrating biofilm. If biofilm
buildup is suspected, the introduction
of appropriate chemicals and physical
agitation is required to remove the
biological plugging material.