14.2 Conserving Groundwater Key Idea: Groundwater is an important resource whose availability is threatened by overuse and by pollution

We Learn: 1. What a water budget is. 2. About some of the causes of groundwater depletion and sources of pollution. 3. How to preserve and protect the groundwater.

What Is a Water Budget?  The water budget is the balance between the water that reaches the ground as precipitations, and the water that leaves the ground as evaporation, runoff, and consumption.  If the amount of precipitation of a region is greater than the evaporation and consumption added together, then that region has a positive water balance, or surplus.  If, the amount of precipitation is less than the usage and evaporation, then the region has a negative water balance, or deficit.

The Water Cycle

Factors Controlling the Water Budget of a Region The water budget of a region is influenced by many natural factors and human activity. Some of the natural factors are:  Climate conditions  The characteristics of soil  The type of vegetation  The type of underlying rocks, etc.

Factors Controlling the Water Budget of a Region 1.Climate encompasses the temperatures, humidity, atmospheric pressure, winds, rainfall, atmospheric particle count and numerous other meteorological elements in a given region over long periods of time, as opposed to the term weather, which refers to current activity of these same elements. meteorologicalweathermeteorologicalweather

Factors Controlling the Water Budget of a Region  When the air temperature is high, plants use more moisture and in the same time the evapotranspiration is high.  When the temperature is low, plants may not use as much moisture, thus the evapotranspiration is low.  A moisture surplus occurs when the rainfall is greater than the need for moisture and the soil water storage is filled. At this point, the soil moisture is recharged, and the surplus percolates into the groundwater, rising the water table.  If the need for moisture is greater than the rainfall, the plants draw water form the soil; this is the time for soil water usage.

Groundwater Conservation  About 50% of drinking water in the US comes from groundwater.  Groundwater is a very valuable resource, and it is in great demand.  Human use threatens the aquifers in two ways: 1. overuse 1. overuse 2. pollution 2. pollution

Overuse of Groundwater If we take out more water than the aquifer can naturally recharge each year, then the consequences are dramatic, and in many cases irreversible:  Wells can dry, and human communities have no water!  In coastal areas, by pumping put the fresh water, salty water will take its place.  By removing the water, the rocks become more compact, and the surface of the ground sinks. This phenomenon is called subsidence.

Coastal Wells Salinization

Subsidence  By removing water from the subsoil the ground becomes more compacted. This is an unwanted phenomenon for two main reasons: - once the porosity of the rocks is lost, the aquifer can not be recharged. - once the porosity of the rocks is lost, the aquifer can not be recharged. -secondly, if the ground loses some of its porosity, it reduces its volume, and sinks. San Joaquin Valley in California subsided in some places over 9 yards, only in half of century. -secondly, if the ground loses some of its porosity, it reduces its volume, and sinks. San Joaquin Valley in California subsided in some places over 9 yards, only in half of century.

Methods Used to Fight Overuse Artificial methods are used to replenish the aquifers.  The used household water is pumped back into the ground through wells.  Water is also pumped into ponds and allowed to seep back into the ground.

Plant to Replenish Groundwater

California  In the San Jacinto Valley, dozens of wells -- some as deep as 1,000 feet or more -- pump 40,000 to 50,000 acre-feet of water each year, about 10,000 acre-feet more than what goes in on average.  As the water table drops, so must the wells, which means more energy -- and more money -- is needed to pump.

Groundwater Pollution  Groundwater is recharged by rain seeping down through the soil.  Virtually, any harmful chemical that is disposed at the surface of the ground will reach the groundwater.  Some common pollutants are: -fertilizers and pesticides -fertilizers and pesticides -toxic wastes berried in the ground (common practice in the past) -toxic wastes berried in the ground (common practice in the past) -accidental spills -accidental spills -farm wastes -farm wastes -sewage from septic tanks, etc -sewage from septic tanks, etc

Groundwater Use and Pollution

Sources of Groundwater Pollution

Sources of Water Pollution

One Billion people Lack Clean Drinking Water

Reducing Groundwater Pollution There is no simple or inexpensive way to purify polluted groundwater. Further pollution can be controlled, or reduced by:  Reducing the use of pesticides and fertilizers  Using environmental friendly chemicals in agriculture  Proper disposal of toxic wastes.

Household Toxic Chemicals What should we do with them?

Proper Disposing of Hazardous Wastes