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Slide 17

When this happens “communication” and pollution of the good groundwater strata can occur in a number of ways.

Rain can wash across cow pastures and other polluted surfaces and wash bacteria and other contaminants into the open un-cemented annular space and into the good ground water strata (and from there up the surface owner’s water well).

The house in the picture has a septic tank and drain field system.  Bacteria from that system in its shallower layer of dirt can move into the annular space and down into the good groundwater (and from there up the surface owner’s water well).

If the lack of cement is deep enough, water from the bad ground water strata can migrate upward into the good ground water strata.  (Not shown.)

If this problem occurs the driller tries pump cement down from the surface through a hose or “tube” into the open annular space.  This is called "grouting".  Grouting is not as reliable as "circulating" cement down the center of the casing and up the annular space until it returns to the surface.  See the previous slide regarding voids caused by mined out coal seams.