About half the population in the United States relies to some extent on groundwater as a source of drinking water, and still more use it to supply their factories with process water or their farms with irrigation water. However, if all water uses such as irrigation and power production are included, only about 25 percent of the water used nationally is derived from groundwater. Still, for those who rely on it, it is critical that their groundwater be unpolluted and relatively free of undesirable contaminants .
A groundwater pollutant is any substance that, when it reaches an aquifer , makes the water unclean or otherwise unsuitable for a particular purpose. Sometimes the substance is a manufactured chemical, but just as often it might be microbial contamination. Contamination also can occur from naturally occurring mineral and metallic deposits in rock and soil.
For many years, people believed that the soil and sediment layers deposited above an aquifer acted as a natural filter that kept many unnatural pollutants from the surface from infiltrating down to groundwater. By the 1970s, however, it became widely understood that those soil layers often did not adequately protect aquifers. Despite this realization, a significant amount of contamination already had been released to the nation’s soil and groundwater. Scientists have since realized that once an aquifer becomes polluted, it may become unusable for decades, and is often impossible to clean up quickly and inexpensively.
Types of Groundwater Contamination
Groundwater pollution caused by human activities usually falls into one of two categories: point-source pollution and nonpoint-source pollution.
Point-source pollution refers to contamination originating from a single tank, disposal site, or facility. Industrial waste disposal sites, accidental spills, leaking gasoline storage tanks, and dumps or landfills are examples of point sources. Chemicals used in agriculture, such as fertilizers, pesticides, and herbicides are examples of nonpoint-source pollution because they are spread out across wide areas. Similarly, runoff from urban areas is a nonpoint source of pollution.
Because nonpoint-source substances are used over large areas, they collectively can have a larger impact on the general quality of water in an aquifer than do point sources, particularly when these chemicals are used in areas that overlie aquifers that are vulnerable to pollution. If impacts from individual pollution sources such as septic system drain fields occur over large enough areas, they are often collectively treated as a nonpoint source of pollution.
Some groundwater pollution occurs naturally. The toxic metal arsenic, for instance, is commonly found in the sediments or rock of the western United States, and can be present in groundwater at concentrations that exceed safe levels for drinking water.
Radon gas is a radioactive product of the decay of naturally occurring uranium in the Earth’s crust. Groundwater entering a house through a home water-supply system might release radon indoors where it could be breathed.
One of the best known classes of groundwater contaminants includes petroleum-based fuels such as gasoline and diesel. Nationally, the U.S. Environmental Protection Agency (EPA) has recorded that there have been over 400,000 confirmed releases of petroleum-based fuels from leaking underground storage tanks.
Gasoline consists of a mixture of various hydrocarbons (chemicals made up of carbon and hydrogen atoms) that evaporate easily, dissolve to some extent in water, and often are toxic. Benzene, a common component of gasoline, is considered to cause cancer in humans.
Another common class of groundwater contaminants includes chemicals known as chlorinated solvents. One example of a chlorinated solvent is dry-cleaning fluid, also known as perchloroethylene. These chemicals are similar to petroleum hydrocarbons in that they are made up of carbon and hydrogen atoms, but the molecules also have chlorine atoms in their structure.
As a general rule, the chlorine present in chlorinated solvents makes this class of compounds more toxic than fuels. Unlike petroleum-based fuels, solvents are usually heavier than water, and thus tend to sink to the bottoms of aquifers. This makes solvent-contaminated aquifers much more difficult to clean up than those contaminated by fuels.
Groundwater typically becomes polluted when rainfall soaks into the ground, comes in contact with buried waste or other sources of contamination, picks up chemicals, and carries them into groundwater. Sometimes the volume of a spill or leak is large enough that the chemical itself can reach groundwater without the help of infiltrating water.
Groundwater tends to move very slowly and with little turbulence, dilution, or mixing. Therefore, once contaminants reach groundwater, they tend to form a concentrated plume that flows along with groundwater. Despite the slow movement of contamination through an aquifer, groundwater pollution often goes undetected for years, and as a result can spread over a large area. One chlorinated solvent plume in Arizona, for instance, is 0.8 kilometers (0.5 miles) wide and several kilometers long!
Depending on the complexity of the aquifer and the types of contamination, some groundwater cannot be restored to a safe drinking quality. Under these circumstances, the only way to regain use of the aquifer is to treat the water at its point of use. For large water providers, this may mean installing costly treatment units consisting of special filters or evaporative towers called air strippers. Domestic well owners may need to install an expensive whole-house carbon filter or a reverse osmosis filter, depending on the type of contaminant.
Source: Water Encyclopaedia
Groundwater pollution is becoming more prevalent; ‘borehole’ water can no longer be considered safe to drink, always test it for contamination. Groundwater can be contaminated by E.coli bacteria and chlorinated solven ts (amongst numerous other harmful substances and organisms). Chlorine-contaminated ground water can possibly allay fears of E.coli and microbial pathogens but chlorine in itself is harmful to many other lifeforms, including humans. Volatile organic compounds (VOCs) can potentially form when substances containing chlorine are released into the environ ment; these can also be extremely hazardous to health. This is good reason to prevent your swimming pool backwash water from entering the environment. Water Rhapsody’s Poolside Tank reuses swimming pool backwash water so that none of it leaves your pool system; saving the environment, saving water and saving you money. Where chlorine is used to disinfect drinking water, special steps should be taken to prevent over-chlorination. When possible, more eco-friendly methods should be employed to render water safe for drinking and bathing. Rainwater harvesting (rooftop rain water collection then stored in water tanks) is one solution to a contaminated groundwater supply. See our product demo for a simple explanation of all Water Rhapsody’s water systems (including greywater recycling systems).