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Groundwater Contamination


Contamination of groundwater supply can occur as a result of natural processes as well as industry and agriculture. Probably, the most lethal and extensive groundwater pollution problem globally is actually natural in origin: the contamination of groundwater with high concentrations of arsenic. Approximately 100 million people globally are exposed to high levels of arsenic in groundwater. Nowhere is the problem more devastating than over large regions of Bangladesh and the West Bengal region of India, where millions have been poisoned by arsenic. This area is intensively irrigated, which has changed the flow of groundwater over a large region. As a result, a shallow aquifer is the source of groundwater for 35-77 million inhabitants who obtain their water from shallow tube wells.

Arsenic in Groundwater

Choropleth map showing the percentage of wells in Bangladesh with high arsenic levels A man using a tube well in Bangladesh Hands palm up showing skin lesions formed as a result of exposure to high levels of arsenic

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High levels of arsenic in this water likely derive from microbial activity that dissociates arsenic from organic material. Arsenic is highly poisonous and carcinogenic and long-term exposure to it can lead to high incidences of skin lesions, bladder, lung, skin and kidney cancer, respiratory disease, and liver and kidney disease. Because the threatened regions are heavily populated, this pollution has made millions of people sick and caused thousands of deaths each year. Even though the hydrology of the affected areas is not well understood, the solution to the arsenic contamination issue involves a combination of extensive monitoring, closing down high-concentration wells, distribution of filters and chemicals to remove arsenic from drinking water, and ultimately tapping deeper aquifers.

The following video provides an overview of the arsenic problem in Bangladesh.

Video: Bangladesh: Traces of Poison in Water (5:03)

Click here for a transcript of the Bangladesh: Traces of Poison in Water video.

Announcer: From United Nations television: This is UN In Action.

Narrator: Bangladesh awash with an abundance of water. Monsoon rains blanket the country during the wet season. All over the countryside, thousands of shallow wells have been dug using this traditional technique.These wells offer life during the long, dry season: water to drink, water to clean, water to live. But in early 1990s, dangerous levels of arsenic water were detected in these shallow wells. Suddenly, an unseen poison threatened Bangladesh's water supply. The crisis has led to a long and arduous search for safe water in the country over the past 20 years. Dr. M. Khaliquzzaman from the World Bank.

Dr. M. Khaliquzzaman: The arsenic issue was identified in the early 90s in Bangladesh, and roughly about 35% of the whole country is now infested with this problem. The amount of people involved is more than 50 million. So, this is a huge, huge problem.

Narrator: Almost overnight, one of the country's bountiful blessings became a deadly curse. Yan Zheng from UNICEF.

Yan Zheng: Arsenic is very interesting because interacts with cells the genes in many, many different ways. So, it is a toxin. It's probably one of the only environmental toxins that attacks more than one organ in human body. And it also causes various gene mutation or expression differences that other environmental carcinogens just incapable of doing.

Narrator: This villager has dealt with the effects of arsenicosis for over 20 years. Arsenic can create painful lesions on the skin and cause various cancers.

Villager (translation): It was hurting so much, I wanted to cut it out.

Narrator: As part of the arsenic mitigation efforts,, the International Atomic Energy Agency (IAEA), in collaboration with the Bangladesh Atomic Energy Commission, has used nuclear techniques since 1999 to help locate safe water. Called isotope hydrology, they discovered that arsenic occurred naturally in the groundwater. By analyzing the age of groundwater and tracking its movement, they have helped predict where safe water can be found. Once the cause was discovered, villages were discouraged from digging shallow wells. Water from this well might be used to clean clothes but will not be safe for drinking or cooking. Nasir Ahmed from the Bangladesh Atomic Energy Commission.

Nasir Ahmed: This shallow aquifers is highly contaminated. The deep aquifer is one of the solutions for providing the safe and sustainable the water supply to the rural people.

Narrator: Working in 12-hour shifts, these men drill deep into the ground to find safe water for a village. It will take a week to reach 700 feet, where water is free from arsenic. In the town of Chapai Nawabganj, the IAEA and World Bank have used isotope analysis to find safe water. The discovery helps Bangladesh to save lives and money and investments needed for arsenic removal and water treatment plans. People now know that the best treatment for arsenic poisoning is drinking safe water, says this villager.

Villager (translated): If we get safe water, that's the real medication for us. Water is life. No one can live without safe water.

Narrator: Enormous progress has been made in projects like these over the past 20 years. Yet more needs to be done to ensure that clean drinking water in this country would remain arsenic-free long into the future.

This report was produced by Dana Sachetti for the United Nations

Schematic showing potential sources of contamination in drinking water like urban run off, leaking sewers, landfills, oil storage tanks, pesticides, etc
Potential sources of contamination in drinking water

Pollution from agricultural and industrial sources is common, although not always as lethal as arsenic poisoning. Typical sources of industrial pollution include solvents, gasoline and other hydrocarbons, paint, and heavy metals. Pollution from agricultural sources includes pesticides, herbicides, and fertilizers. Many of these pollutants are carcinogenic. Both sources of pollution can lead to the growth of toxic microbes. Agricultural and industrial runoff can deliver pollutants into groundwater systems

Human and agricultural sewage is another potential source of pollution. This pollution leads to a variety of different impacts on health all the way from gastrointestinal illness to, in severe cases, cholera, typhoid, amoebiasis, giardiasis, and E. coli.

The following video explains the sources of groundwater contamination.

Video: Groundwater Contamination (4:35)

Click here for a transcript of the groundwater contamination video.

Narrator: Do you know where your drinking water comes from? Do you know what happens to all of the chemicals that you use day to day? Things such as cosmetics that wash down the drain? Pharmaceuticals that flush down the toilet? Motor oil running off parking lots, and even paint down a drain? Many of these chemicals eventually make it into the water that flows underground. Dr. Barb Mahler, a scientist at the United States Geological Survey, an adjunct professor at the University of Texas, is studying what happens to chemicals like these after most of us forget about them.

Dr. Barb Mahler: Most people don't think about the fact that there's water underground. And what happens is when it rains, some of that water infiltrates into the surface, and some it makes it all the way down to the water table. And that water table isn't static, water actually moves underground. And so, that's why we have water in creeks. Water is flowing underground and discharging into creeks, and then it becomes surface water. In karst aquifers, the water is flowing through spaces that have dissolved out of the rock. And we don't usually think of rock as dissolving. I mean, granite doesn't dissolve. And that's the interesting property that limestone has, is that when it comes into contact with water that's just a little bit acid, like rain water's a little bit acid, soil water is even a little bit more acid, there's a chemical reaction. And the rock, itself, dissolves.

Karst aquifers, such as the Edwards Aquifer in Central Texas, can be more vulnerable to contamination. But why is this? Dr. Mahler is studying what happens in aquifers with a class of contaminants known as PAHs.

Dr. Mahler: You can kind of imagine, most aquifers you could think of as a big sandbox. And the karst aquifer you'd think of maybe as a block of concrete that you'd cracked and then dissolved out some tubes through it, a system of tubes. And if you were to pour something poisonous, like a pesticide or an herbicide, or some other type of contaminant, on top of those two systems, that it would move really slowly through the sand grain aquifer. And some of it would stick to the sand grains and some of it would get filtered out. Whereas, in the karst aquifer, it would just be funneled, or focused, into those zones of what we call preferential flow, those pipes going through the rocks. So, in karst aquifers there's this very important interaction between what goes on at the surface and what goes on underground, because they're so closely connected. So, really anything that we use at the surface is going to find its way underground, and it's going to find its way underground quickly, and it's going to move through the underground very, very quickly to come out at springs. One category of contaminants are pesticides: insecticides, herbicides, things that we put on our landscaping and our gardens and on golf courses to try and control weeds and try and control pests. Well, those things are, by design, toxic. They're meant to kill things, so they are contaminants. And whenever it rains, they wash off the surface and they go into the groundwater system, and they can move very quickly, sometimes in a matter of hours, from the surface to come out at Barton Springs. Another category of contaminants that we're all familiar with are things like gasoline, gasoline spills and oil spills. Also, leaking from underground gasoline storage tanks. Those can enter karst aquifers very quickly and can cause contamination that can move through the system in pretty much the same concentrations that we find them at the surface, they could come out the springs. Yet a third kind of contaminant is sediment, and contaminants that are associated with sediments. So, there are some contaminants that tend to adhere to sediment. And if the sediment moves through the system, they'll bring those contaminants with them. The reason that you find them in karst is that the openings in the subsurface are large enough for contaminants on sediment to move through and for that sediment to not get filtered out. So, these are contaminants that sorb to solid phases, rather than being dissolved in water, and in karst systems, we can find those as well.