Course: BFM 203 Water Treatment and Control

Lecture

Ground Water

Ground Water

Ground water is generally characterized by higher concentrations of dissolved solids, dissolved gasses, lower levels of color, relatively high hardness, and freedom from microbial contamination. Microbial contamination in ground water may indicate that it is under the direct influence of surface water and must be treated as surface water. A microscopic particulate analysis is used to determine the potential influence by surface water.

These groundwater characteristics vary by region as well as by depth. Infiltration of precipitation into the soil replenishes solid moisture or is used by plants for growth. Water that percolates below the root zone finally reaches a level at which all of the openings or voids in the earth's materials are filled with water. This zone of saturation is called ground water. When the upper level of the zone of saturation is not confined by impermeable material, it is referred to as the water table. If it is confined by impermeable material, is is under artesian pressure.

The illustration below is a depiction of the water table.

Wells

A well that penetrates the water table is used to extract water from the groundwater basin. Pumping water will cause a natural lowering of the water table near the well. If the pumping rate exceeds the rate of replacement by water-bearing formations, the sustained yield of the well will be exceeded. The safe yield will be exceeded over a period of time if the extraction rate depletes the aquifer and brings about undesired results such as seawater intrusion or land subsidence. Multiple wells located close to each other may decrease the production of each well because of interference. This interference is due to an overlap in the circle of influence of each well.

Springs

A "spring" is comprised of ground water that flows naturally from the ground. The flow may be caused by gravity OR by artesian pressure. Flow of water into the spring fluctuates with pressure changes. Gravity springs are more likely to be biologically contaminated than artesian springs. The image below depicts the actual or potential flow of water from the aquifer up through artesian wells, flowing artesian wells, or water table wells.

Source: http://www.ec.gc.ca/eau-water/default.asp?lang=En&amp;n=300688DC-1#sub2