The Water Cycle describes how water travels through the environment. Water continually recycles itself, moving from the soil’s surface to runoff and seepage underground, through the atmosphere and back to the surface.
Runoff is the movement of water from precipitation. Storm water collects in rivers, lakes, and oceans where it is considered surface water. Some runoff infiltrates soil and supports the growth of vegetation. Percolation downward through rock and soil below the root zone adds to groundwater storage. Groundwater is held in underground soil pore space where it can be access by domestic wells
Evaporation occurs as water is returned to the atmosphere in the form of vapor.
Condensation is the cooling of water vapor until it liquefies, causing clouds in the atmosphere, and eventually becoming rain or snow.
Precipitation is moisture that falls as rain, snow, sleet or hail and adds to surface water and groundwater storage.
Water Ownership
In many states, including Oregon, all water is publicly owned. With some exceptions, cities, farmers, factory owners, and other water users must obtain a permit to use water from any source, whether water is underground, or from lakes or streams. Generally speaking, landowners with water flowing past, through, or under their property do not automatically have the right to use that water.
Water Use Regulation
Water use is monitored at every governmental level, with states having prime regulatory authority. For example, Oregon’s water laws are based on the principle of prior appropriation. This means the first person to obtain a water right for a stream is the last to be shut off in times of low stream flows. During water shortages, the water-right holder with the oldest date of priority can demand the water specified in the water right regardless of the needs of junior users. If there is a surplus beyond the needs of the senior right holder, the water right holder with the next oldest priority date can take water to satisfy needs under their right and so on down the line until there is no surplus or until all rights are satisfied.
For more information regarding water rights see EPA website. www.EPA.gov.
Ground Contamination
The United States employs groundwater as a critical natural resource. In addition to agricultural and industrial uses, half of the U.S. population depends on groundwater for household drinking water. While the EPA estimates that less than 2 percent of the Nation’s groundwater is contaminated, this tends to be concentrated near heavily populated areas. As groundwater demand increases these areas are challenged to provide adequate drinking water.
Residential Areas
Groundwater is a storage area for freshwater. Contaminants in other parts of the hydrologic cycle, such as the atmosphere or bodies of surface water, can be transferred into groundwater supplies through movement and flow of this cycle. As residential communities grow, increasingly large paved areas funnel storm water directly into local streams and lakes. Runoff from streets, roofs, construction sites, and landscaped areas concentrate pollutants. Contaminants that would ordinarily percolate slowly into the soil now accumulate and run into storm drains and streams that cannot handle the volume and concentration.
Household Hazardous Waste is routinely added to landfills not equipped to handle them. Improper storage and disposal of batteries, detergents, disinfectants, gasoline, medicines, paints, solvents, pesticides, and pool chemicals can lead to ground water contamination.
Fertilizers, herbicides, insecticides, fungicides, and pesticides applied to lawns and gardens contain hazardous chemicals that can flow into storm drains or travel through the soil to contaminate groundwater.
Salt is used to melt snow for winter driving. Each year more than 11 million tons of salt are applied to roads in the United States. This salt is washed directly into the surrounding soil and water.
Septic systems are designed to slowly drain away human waste underground at a slow, harmless rate. An improperly designed, located, constructed, or maintained septic system can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater.
Agriculture and Industry
There are more than 65,000 synthetic organic contaminants (SOCs) commonly used in the U.S., the greatest quantities of which are generated during the normal course of business. Not surprisingly, EPA ground water surveys conducted over the last decade confirm the widespread occurrence of organic contaminants, mainly due to their extensive use.
Hazardous waste is stored in containers that eventually degrade and leak, allowing waste to seep into soil, wash into streams, and make its way into groundwater. In the United States today there are estimated to be more than 20,000 abandoned and uncontrolled hazardous waste sites, with more added every year.
Landfills have a protective barrier to prevent contaminants from leaching into the water. However, in old landfills, or if there is a damaged or absent barrier, contaminants can leach into the groundwater. Toxicity Corrosivity Leaching Procedure (TCLP) analysis is performed to determine the effects of time and environment on landfill samples.
Underground Storage Tanks (USTs) can corrode, crack and develop leaks, releasing petroleum products, acids, solvents or chemicals into the environment. When these liquids get into the groundwater, serious contamination can occur. There are estimated to be more than 10 million storage tanks buried in the United States.
Natural Contaminants
Groundwater moving through sedimentary rocks and soils accumulates a range of compounds such as magnesium, calcium, and chlorides. Some aquifers have high natural concentration of dissolved elements such as arsenic, boron and selenium.