1. Chapter 10 Groundwater (Cont’d) Groundwater Systems The average length of time that groundwater remains underground is several hundred years. Groundwater moves slowly but continuously through aquifers and eventually returns to Earth’s surface. Groundwater emerges wherever the water table intersects Earth’s, commonly in areas that have sloping surface topography.

2. Aquifers and Aquicludes- Formation of Springs Aquifers are permeable underground layers through which groundwater moves with relative ease - underground streams in cavernous limestone formations may transport water at a rate of several kilometres per day. Aquicludes are impermeable layers that block groundwater movement (e.g., layers of clay or shale). Groundwater tends to discharge at Earth’s surface where an aquifer and an aquiclude come into contact producing Springs. Fig. 10-12

3. Springs The volume of water that is discharged by a spring may be a mere trickle, or, in karst regions, an entire river may emerge from the ground. Most springs have a temperature the is equal to the average annual temperature of the region in which it is located. However, in some areas, spring temperatures can be warm to hot – Hot springs, Geysers. In the western half of the continent this is primarily due to recent igneous activity, where as in the eastern half of our continent it is a result of springs emerging from aquifers that descend to great depths in the Earth’s crust allowing deep, hot water to rise. Fig. 10-13, 10-14

10. Wells and Confined Aquifers Wells - To produce a water, a well must tap into an aquifer. Specifically, drilled below the water-table, into the zone of saturation, and into what is called the water-table aquifer. Drawdown, Recharge Fig. 10-15, 10-16 Confined Aquifers – Water-table aquifers are unconfined and unprotected, and thus easily polluted. Surface spills of pollutants often reach the water table and spread throughout aquifers. Confined aquifers, are deeper in the Earth’s surface, generally confined between aquicludes, and are less easily polluted. Artesian Wells

11. Threats To Our Water Supply Freshwater is Earth’s most valuable natural resource. Human demands for fresh water are enormous – household, industry, agriculture. Specific threats include: – Overuse – Subsidence – Pollution of Groundwater – Chemicals – Salt – Radon Fig. 10-17 Fig. 10-18

12. Questions: Pg. 257 1.How are springs related to the water table? 2.What is the basic characteristic of an artesian well? 3.List four common sources of groundwater pollution. 4.Why are chemical contaminants a serious pollution problem in groundwater? 5.Artesian aquifers contain underwater pressure. Explain why. 6.What can you do to conserve and protect groundwater so that there will be safe and abundant water supplies in the future?