River Water Is Now Flowing Into Aquifers Through Highly Contaminated Sediments

 

Large-scale groundwater pumping is opening doors for dangerously high levels of arsenic to enter some of Southeast Asia’s aquifers, with water now seeping in through riverbeds with arsenic concentrations more than 100 times the limits of safety, according to a new study from scientists at Columbia University’s Lamont-Doherty Earth Observatory, MIT, and Hanoi University of Science.

Normally, groundwater levels in this monsoon region are higher than the rivers, so water flows from aquifers into adjacent waterways. A few years ago, however, scientists began noticing that large-scale groundwater pumping around cities like Hanoi was lowering the groundwater level, so much so that the flow had reversed in some areas and river water was making its way into the aquifers instead.

The scientists have since tested the water and riverbed along the Red River near Hanoi and discovered dangerously high concentrations of dissolved arsenic, far higher than expected, but they also found clear patterns of contamination that may be able to help farmers and communities locate lower-risk sites for wells.

The findings, appearing in the American Geophysical Union journal  Water Resources Research , carry important lessons for groundwater management in a region that has long struggled with health effects of arsenic contamination. Arsenic in groundwater is a problem in many countries, including parts of the United States, but it is widespread in Southeast Asia, where its impact on poor communities has been described as thelargest mass poisoning in history. Long-term exposure can cause liver and kidney damage and skin cancers that cause sores on the hands and feet. Arsenic can also affect crop yields.

 “We have this perception of groundwater as this giant underwater lake, a nearly infinite resource. But even in places were the water is rapidly recharged, using it a lot can move water around in ways that affect the location and extent of contamination,” said coauthor Ben Bostick, a geochemist at Lamont, who with coauthor Alexander van Geen of Lamont has been working for over a decade with communities in Vietnam, Cambodia and Bangladesh to avoid arsenic contamination and locate safer water sources.

Patterns of contamination

In Hanoi, groundwater pumping doubled during the 2000s to an estimated 240 million gallons a day by 2010, and groundwater levels there have been dropping by about 1 meter per year. The effects have become evident in the village of Van Phuc, about 10 kilometers downstream, where arsenic from riverbed sediments has started to contaminate an older aquifer that had long been considered clean.

For the new study, the scientists traveled along the Red River using a device that looks like a syringe with a very long needle to take samples of riverbed sediment and water at a depth of 1 meter.  They found the highest arsenic levels in areas where the river flow was slow and new sediment was being deposited, typically next to land inside a river bend.  Young sediments can be highly reactive and susceptible to releasing arsenic as water flows through them.  The sediments in these slow-water areas were less than 10 years old in places, and they were releasing arsenic into groundwater at concentrations exceeding 1,000 micrograms per liter, 100 times higher than the World Health Organization considers safe.

In contrast, almost all of the wells near faster-flowing water – where little new sediment was accumulating – tested below the WHO limits.

“Prior to intensive pumping, the water would not have been flowing through these sediments, and the aquifer would not have been drawing in this much arsenic,” said Mason Stahl, lead author of the study and a recent Ph.D. graduate of MIT.  "If groundwater pumping continues – and it will probably intensify – the contamination will continue to migrate.”

South and Southeast Asia are especially susceptible to arsenic poisoning because their low-lying deltas are largely made up of young sediments and have plenty of organic matter that contributes to the release of arsenic into water.  

The Red River’s arsenic generally comes from iron oxides carried downstream from the mountains. When iron oxides are deposited along the riverbed, they are in an environment that is low in oxygen and high in organic matter, from sources such as plant matter and sewage. Bacteria reduce the iron oxide to release oxygen, and that natural process allows the arsenic to enter the water. The process is fast. Within a few months, the scientists measured concentrations up to 1,500-2,000 micrograms per liter from new sediment.

Lowering the risk

The results suggest that for pumping, communities should still target the oldest aquifers, where sediments are no longer being deposited and most of the arsenic has leached out. But they also need to think about other potential arsenic sources – such river bends with fresh sediment.

“The good news is that rivers normally meander, and cities very seldom are the size of one meander,” Bostick said. Cities can put their well fields in areas where the aquifers aren’t being recharged through young river sediment, he said. Damming a river would also keep sediment back and control the river’s height, but dams can pose other challenges by changing sedimentation, ecology and the water budget.

Water treatment and filtration are also becoming more common, and Bostick believes this may be the most effective solution. The arsenic is not going to go away overnight, and pumping for irrigation will have to continue so farms can feed the region’s large population. “Although groundwater has a lot of advantages, you also have to really think about how much you want to use it. With technology, it’s pretty easy to clean surface water to use it now,” Bostick said.

Michael Puma, an expert on water and food security at NASA’s Goddard Institute for Space Studies who was not involved in the study, noted that “Arsenic contamination of groundwater threatens well over 100 million people worldwide. These important findings will help us as we strive to manage and improve the quality of drinking water, especially for those living in extreme poverty around the world.”

The other coauthors of the new study are Charles F. Harvey of MIT; Jing Sun of Lamont; and Pham Thi Kim Trang, Vi Mai Lan, Thao Mai Phuong and Pham Hung Viet of Hanoi University of Science.

Attached link

Taxonomy

• Arsenic
• Groundwater
• Aquifer Recharge
• Groundwater Recharge
• Groundwater Pollution
• Groundwater Mapping

2 Comments

1. I think that this solution is useful even in this case. http://www.spawhe.eu/the-sustainable-future-of-environment-energy-food-and-labour/

   VERTICAL DESALINATORS - DEMINERALIZERS BY ION EXCHANGE WITH HYDROELECTRIC ENERGY PRODUCTION
   Abstract The state of the art in the development of desalination and demineralization treatment of marine and brackish water has been conditioned, as many other industrial systems, depuration, energy and protective of the environment, by the absence of synergies between the pumps and hydraulic turbines and from the incorrect approach to the gravitational force, which is not to be won by lifting hydraulic but sustained, with a one-way circulation of water in open reservoirs, upper seats that double as hydraulic backflow preventers. With the triple synergy between the dual supply pumps, turbines and recycling of water in an open vessel, applying hydraulic principles known for centuries, such as the principle of communicating vessels, the laws of Bernoulli and Pascal, strategically placing the electric double suction pumps between a high positive hydraulic head and the turbines, dimensioned for the exploitation of the same hydraulic load, the pumps, working with a balanced load, with a small energy consumption, they win the state of inertia, allowing the energy transformation of pressure of the intubate water column overlying the pump, into kinetic energy and transferring it to the turbines, which produce energy. These spheres, floating climbing ion exchanger and descend by gravity, emptying water in downhill tubes. By means of diverters change the path compared to the flow to be immersed in the washing tanks and regeneration of the resins, and reinserted again, indefinitely, in ion exchange circuit without interruption of the desalination
   5
   cycle and energy production and without costs for heating the water or replace the membranes. The demineralized water serving for the washing of the resins is produced by continuing the process through a mini system completely similar to the main that part from the desalinated water tank. If men want to produce desalinated water in industrial quantities that serve humanity, also desalination plants, as purifiers and water lifting and distribution, must become producers of energy, not consumers, supporting, not opposing gravitational forces. The sustainability of global systems is not based on complicated technology but on synergies between simple and rational systems. Description
   In the present state of the technique of desalination and demineralization are headed three types of installations: by evaporation, permeation through membranes, for ion exchange. Currently, the difference between the three systems, mentioned above, makes it especially the cost of treatment. That evaporative, produces water free of mineral salts and with acid pH, therefore for the use of water is required a subsequent mineralization and neutralization of the pH.
   The filtration with membranes entails high operating pressures, therefore high energy consumption and the high cost of the membranes, which periodically must be replaced.
   The one with the ion exchange resins involve a complex filtration, washing and regeneration circuit of the resin, with reverse flows that involves the dispersion of apart of the resins in waste waters of the processes.
   All processes are heavy on energy consumption for heating or for circulating pressurized water in filtration and regeneration systems. The operating costs are around 1.5 euro / mc with reverse osmosis plants, which are the most used, but also the investment costs are significant, being about 1000 Euros per m3 / day of desalinated water produced. It 'obvious that with these production and investment costs, the desalinated water can be used only for potable use. It 's impossible to think to use it for industry and agriculture. With the solution that proposes the agricultural and industrial use will become a competitive reality also with wells and other purification systems, which are in any case forced to treat polluted water, or with scarce mineral requirements. In fact, the sea water being rich in mineral salts, If desalination becomes sustainable, can become the best natural fertilizer for land, being able to send the
   6
   same water can be used as fertilizer treated tailored to the target terrain, both in terms of mineral salts that alkalinity. For transport the desalinated water to considerable distance there is no problem, because with the dual supply pumps coupled to the hydraulic turbines, also the transport and the lifting of the water becomes a source of energy, not of consumption. In fact, the key to solving many environmental and energy problems, including desalination, is to realize Hydraulic and hydroelectric circuits using otherwise the pumps and turbines.
   At the state of the art the desalination system least used is the one with the ion exchange, but this system is the most suitable to be used in conjunction with the dual supply pumps and turbines, not having the necessity of high temperatures or high operating pressures than competing systems. Therefore, the high cost of the resins and of the reagents liquid, required for regeneration, can be largely compensated by low energy consumption, energy production produced by the plant and low cost required for plant, and low operating and maintenance costs. Furthermore, with the solution described below, it will also solved the problem of the dispersion of the resins in water and process liquids, being the resins contained and circulating (in water and chemical reagents) in perforated polyethylene spheres with holes pass below the size of the same. We can say, that the new solution is opposite to the current of ion exchange solutions, where the resins are stopped and the liquid passes through them, both in the reaction phase than in those of washing and regeneration. With the system proposed resins are circulating in the water and in the regenerating liquid, at low speeds, with long contact times, which provide capillaries contacts. For the circulation exploit physical principles, not energy. Over 90% of energy produced in the plant can be transferred to public power networks. Therefore, the facility is composed of a chemical part, an electromechanical and a hydraulic.

2. @Naizam Thank you for this very enlightening article, particularly regarding the role of riverbed sediments. Is it the iron oxides that also contain the arsenic in association with the iron? You mention that sewage or organics in the water reduce the iron to utilise the chemically bound oxygen. What is the mechanism for the associated As? What is the fate of the reduced iron in the sediments? Thanks