Many cities around the world depend on pumping groundwater for their residents, but there is growing evidence that intensive groundwater pumping under urban landscapes may be detrimental to water supplies and pose health problems that have the long-range potential to kill millions of people who drink it, according to a study by a team of international scientists that includes a Texas A&M University researcher.
Peter Knappett, assistant professor hydrogeology at Texas A&M, and colleagues have had their work published in the current issue of Nature Communications.
Using computer models and field observations, the team used Dhaka, Bangladesh as a prime example of intensive groundwater pumping, noting that such continued use can depressurize deep, drinking water aquifers increasing the chance that those aquifers will be contaminated by drawing down water from more contaminated shallow aquifers.
Shallow aquifers in urban areas are frequently polluted with significant amounts of industrial contaminants. Throughout South and Southeast Asia, widespread naturally occurring arsenic also pollute the shallow aquifers.
Arsenic is a toxin that occurs naturally in sediments around the world, and it can cause death if large amounts are ingested. Exposure to arsenic can also lead to several forms of cancer, heart disease and strokes.
The team found that shallow aquifers contain arsenic levels that can be 100 times greater than those currently allowed under U.S. Environmental Protection guidelines.
"People who drink this water are much at-risk," Knappett explains.
The government of Bangladesh has been rapidly installing deep, community wells throughout the country with the goal of providing a low-arsenic drinking water source to their people, Knappett says.
"In most cases where groundwater is pumped from deep aquifers, the water is very low in arsenic," he notes.
The team points out that worldwide, almost 500 million people live near large cities where groundwater pumping occurs. Dhaka, the capital of Bangladesh, one of the poorest countries in the world, has a population of 9 million, although the broader metropolitan area has close to 20 million people. It is located on one of the largest deltas in the world where some of the most extensive groundwater pumping is used anywhere in the world.
A related study has found that villagers who had been consuming similar water were twice as likely to die over a period of eight years compared to villagers who drank different water.
"The situation is especially worrisome in Southeast Asia because so much groundwater pumping is done in that area," Knappett adds, "and there are no plans in place on how to deal with this potential long-term problem."
Groundwater pumping is often done in Texas and other areas where surface water supplies are not sufficient for population needs.
Areas near San Antonio, Austin, Dallas-Fort Worth and El Paso have seen extensive groundwater pumping in recent years.
"In El Paso, where water supplies have been a problem for decades, there is a lot of groundwater pumping, but in an arid region with little natural recharge the more pumping there is, the greater chances for water to be contaminated by brackish water," Knappett says.
"While still widely present and a concern, in the U.S., arsenic is often not the problem, but rather contaminants such as industrial fluids and even gasoline seeps into the aquafers. Once an aquifer is broadly contaminated on a regional scale similar to the size of U.S. cities, it's finished -- there is no way of reversing the problem.
"The water standards in the U.S. are much higher than most of the developing world," he adds. "But in Bangladesh and other countries, millions of people are at-risk, and it's very possible that urban pumping could contaminate their only reliable source of drinking over the next 50-100 years, with no plan in place to reduce this risk. This is a health crisis waiting to happen."
The study was funded by the National Institutes for Environmental Health Superfund Research Program.
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