Module 1 — Understanding Groundwater
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Natural groundwater recharge is affected by human activities on the ground surface.
For example, the drainage of sloughs removes water that would have infiltrated to eventually
become groundwater. A reduction in groundwater recharge can seriously reduce the water
level in nearby shallow wells. This groundwater/surface water interaction must be carefully
considered because the development of either resource will affect the quantity and quality of
the other.
Factors Affecting Groundwater Quality
An understanding of the factors that affect groundwater quality can help you make
decisions on well depth and the best water quality for a particular application. There are
several factors that affect groundwater quality:
Depth from ground surface
Permeability and chemical makeup of the sediments through which
groundwater moves
Climatic variations.
Depth from Ground Surface
Water is the world’s greatest and most abundant solvent. It attempts to dissolve
everything it comes in contact with. As a result, the longer groundwater takes to move
through the sediments, the more mineralized it becomes. Thus, shallow groundwater
aquifers have a lower level of mineralization, or total dissolved solids (TDS), than deeper
aquifers. Water from deeper groundwater aquifers typically has a much longer trip to its
destination and thus it is usually more mineralized.
While shallow wells have lower levels of TDS, they do have higher levels of calcium,
magnesium and iron than deeper wells. High levels of these minerals make the water
“
hard.” Deeper wells have higher levels of sodium and lower levels of hardness, making the
water “soft.” The reason is that deeper sediments and rock formations contain higher levels
of sodium and as water moves downward through the sediment and rock formations, a
natural ion exchange process occurs. Calcium, magnesium and iron in the groundwater are
exchanged for sodium in the sediment and rock formations. The result is groundwater with
higher levels of sodium and little or no hardness. The process is identical to what occurs in
an automatic water softener, except in this case, it is a natural phenomenon.
Total dissolved solids (TDS) means the
quantity of dissolved minerals in the water.