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THREATS TO DRINKING WATER





Threats are those conditions that would affect people's health if the water is used for drinking, cooking, or general hygiene purposes; and could be either a quality issue or quantity issue.

In many cases, the quality of the drinking water source may make the water unappealing (taste and odor concerns), but does not pose a health threat if consumed, so it is not considered a threat.

Threats to your drinking water system may be either manmade or naturally occurring. Threats to our drinking water sources can be considered as groundwater threats or surface water threats, although since the two are inseparably linked, a problem with one will inevitably mean a problem with the other.

Groundwater Threats
Manmade Threats
Many human activities can negatively affect groundwater quality as well as quantity. For many years it was generally believed that the filtering capabilities of the soil protected groundwater from contamination by human activities on the surface.

But with the discovery in the 1970s of manmade organic chemicals in groundwater, we began to realize how extensively our activities can affect groundwater. In fact, in a nationwide study commissioned by the U.S. Environmental Protection Agency, 65 percent of the private wells tested failed to meet at least one drinking water standard.

Those activities that can have a negative impact on groundwater can be categorized into four groups: waste disposal, resource extraction, agricultural practices, and urbanization.

Waste Disposal
The best known source of groundwater contamination is waste disposal sites (landfills), both municipal and industrial, that were in existence before new regulations went into effect in 1988.

Septic systems are another potential source of groundwater contamination. If septic systems are improperly installed or maintained, bacteria, viruses, nitrate, phosphorus, chlorides, and the organic solvents that are found in many household cleaners as well as products sold to "clean" septic systems can all make their way into groundwater. As a result of poor construction or maintenance of their septic systems, rural homeowners are frequently the cause of contamination of their own wells.

Resource Extraction
As mines intersect aquifers and collect water, they interfere with groundwater storage and can lead to lowered water levels in wells.

Drainage from mining degrades water quality as it infiltrates aquifers or discharges into streams. Increased concentrations of iron, manganese, sulfate, and dissolved solids in well water can result. Stone quarries can have a negative impact on both groundwater and surface water sources.

Agriculture
Common agricultural practices such as fertilizing and applying pesticides are coming under increased scrutiny because groundwater samples have revealed nitrates and, in some cases, pesticides. The most prevalent problem is high levels of nitrate from overapplication of manure and fertilizer. Nitrate is especially harmful to babies, interfering with the blood's ability to transport oxygen, which causes the baby to suffocate ("blue baby" disease).

Urbanization
Many human activities and land use practices, which proliferate with urbanization, can negatively affect groundwater. Even cemeteries, for example, can contaminate groundwater.

One effect of urbanization is recharge diversion. Soils that have been covered with impervious surfaces-roofs, parking lots, or streets-obviously cannot absorb precipitation. Nor can soils that have been compacted by heavy machinery. As a result, much of the water from rain and snowmelt goes directly into streams and is never available to recharge groundwater.

Large concentrations of people can also lead to overpumping of aquifers. This can result in significant aquifer draw down, which in turn reduces the quantity of streamflow. Stream water quality then suffers due to higher concentrations of sewage treatment plant effluent. Intensive pumping in coastal areas can cause salt water to be drawn into aquifers and wells. Polluted stream water can also be drawn into drinking water wells.

With increased population comes industrialization and an increase in the amount and variety of industrial activities, many of which can potentially contaminate groundwater. Leaking storage tanks at both industrial sites and gas stations have contaminated groundwater in many instances.


Natural Contamination
The natural constituents of water that may affect its suitability for drinking and other purposes most commonly found in groundwater are dissolved solids, calcium carbonate, and iron. Concentrations of chlorides and nitrates can also restrict use of water. These constituents enter water by leaching from rocks as water moves through them. Hardness is a property of water, usually measured by the concentration of calcium carbonate, which increases the amount of soap needed to produce lather.

Radon, a naturally occurring radioactive gas formed from decaying uranium or radium deposits, is a natural contaminant of increasing concern. Where radon is present in bedrock, it can dissolve in groundwater and become a health hazard either when consumed or when the gas escapes into the air during showering, cooking, and laundering.

Hydrogen sulfide is an infrequent natural contaminant of groundwater caused by water storage in certain types of shale rock. It imparts a characteristic rotten egg odor to the water, but is not seen as a health threat at the levels at which it makes water unpalatable.

Corrosive groundwater is common. Corrodibility involves many factors including high acidity and low concentrations of calcium carbonate. In a recent Penn State survey of ground water in private wells, 60 percent had corrosive water. Corrosive water dissolves lead and copper from pipes and plumbing fixtures, thus causing a health risk.

Surface Water Threats
Because surface water (rivers, streams, ponds, lakes, reservoirs, and springs) are by their nature more "visible," most people have more experience with this water source. Surface waters are often areas of recreation that provide us with opportunities for swimming, boating, fishing, and camping. Most of us have pleasant memories and experiences related to these water habitats and view them as a wonder of nature, representing crisp, clear, clean water.

While many of the threats talked about in the Groundwater Threats section relate to surface water sources, surface water is even more vulnerable to contamination because of its readily available nature. Surface waters can be contaminated by pollution from "nonpoint sources," sometimes called "polluted runoff," or "point sources," usually permitted discharges from sewage treatment or industrial waste treatment plants.

For more information on contaminants in drinking water visit:

https://www.epa.gov/ground-water-and-drinking-water

http://www.groundwater.org/

https://water.usgs.gov/edu/earthgwaquifer.html


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