U.S. partner Ben Bostick and PI Pham T.K. Trang with water samples(Photo courtesy Dr. Trang).
Arsenic contamination is heterogeneous but widespread in the Red River and Mekong River deltas of Vietnam, where more than 10 million people depend on arsenic-impacted aquifers for drinking and irrigation water. Many of these wells are private tube wells with dangerous levels of arsenic. The Vietnamese researchers conducting this project have been documenting the extent and nature of this contamination for many years in collaboration with scientists from around the world. Development and urbanization has facilitated the installation of numerous domestic water supplies that draw heavily upon low-arsenic parts of the aquifer. These wells provide safe drinking water but have drastically changed the regional hydrology and are beginning to draw contaminated water into previously uncontaminated areas. The long-term sustainability of these precious water supplies needs to be established. To address this need, the project team will sample these and other groundwater resources regionally around the Hanoi area, with the work to involve training of young scientists and incorporation of a comprehensive suite of quality parameters that are indicative both of current and future risks. This will increase local capacity to evaluate these resources and provide the information needed to effectively recommend solutions for the sustainable use of aquifers.
Capacity building will be carried out through a series of training courses that address critical knowledge gaps in evaluating water quality and the effects of arsenic in the environment. The first course to be presented will be on the chemistry of groundwater arsenic contamination. This course would consist of background information about sediment processes, adsorption, and a description of the factors that affect arsenic retention, as well as a discussion of potential remediation options, with a focus on sand filters and others that are locally widespread and useful. These programs will increase the capacity to interpret regional geochemistry and provide students with the knowledge and critical skills needed to make decisions about the sustainable use of their groundwater resources. The results will provide a regional picture of the impacts of large scale regional groundwater withdrawal in one of the most extensively used, and thus possibly one of the most threatened, aquifers in the region. Mutual collaborations that will arise from this work will be invaluable in developing future research projects for this and other pressing issues related to the sustainable use of our environment.
Summary of Recent Activities
The second phase of this PEER project was aimed at determining the chemical reactivity of organic matter found in the aquifer. This was done in a series of microcosm-based laboratory experiments using groundwater obtained from the Van Phuc site, by monitoring the amount of organic carbon over time. First, Dr. Trang and her team measured the concentration of organic carbon in the groundwater, and then they monitored the concentration of organic carbon over time. If the carbon is reactive, bacteria can use the groundwater and the organic carbon concentration will decrease as bacteria “eat” it. In their studies, the team identified a significant level of reactivity in the carbon in their groundwater water samples, and in late 2015 they were examining the radiocarbon ages of the samples to see if there is a link between the age of the organic matter and its utilization by the microbes. The reactivity of organic carbon is very important regionally. The regional sampling described above also documented the introduction of reactive organic carbon to the aquifer regionally. Since this organic carbon can release arsenic into groundwater, its entry into groundwater represents a potentially important threat to groundwater resources.
Although drill core sampling allows researchers to study what is in groundwater at a specific depth, it provides an incomplete description of an aquifer system. Well drilling allows scientists to examine the sediments that control the composition of groundwater and that direct flow, and to do so as a function of depth at a location. Unfortunately, it is also expensive, time-consuming, and obtrusive in that it leaves a physical well where the core is collected. Based on their regional survey, Dr. Trang and her team selected two sites for well drilling. Both sites are believed to be Pleistocene in age (more than 10,000 years old, usually featuring red sands that have no arsenic in the groundwater). Groundwater sampling showed that the Yen My area appears to be much more consistently high in groundwater arsenic than is Van Duc. This could be attributed to differences in sediment age, although the team hypothesizes that it is more likely a reflection of Hanoi pumping, which has disproportionately affected the water quality of Yen My due to its proximity to the pumping source and location relative to the river. Further study is needed on the concentration and chemical form of both organic carbon and iron oxides in the groundwater, however.
Dr. Trang cites several main scientific achievements of her project, including mapping of groundwater composition, documentation of sediment stratigraphy, and evaluation of the sustainability of water resources in the regions studied. Equally important as its scientific goals were the educational and capacity-building aspects of this PEER project. It supported several graduate students for portions of their studies. Most notably, Nhat Minh received his Master’s of Science for his contribution to this project. He was the student most directly responsible for the regional groundwater sampling, and this formed the core of his thesis. Vu Duyen also has been involved in the collection of dissolved organic carbon samples during the project and carried out the experiments examining its decomposition. Both of those efforts were exceptional and are being incorporated into publications in high- caliber journals. Students and staff alike also gained valuable experience in field work, lab techniques, and data management in collaboration with their U.S. counterparts.
By the end of December 2015, Dr. Trang and her group had completed all their proposed scientific activities on the project. They had expected to send at least one researcher to the United States in January 2016 to take part in a multinational collaborative drilling exercise in Illinois coordinate by their U.S. partners. However, that event was postponed indefinitely, so instead Dr. Trang will send a young researcher from her center, Ms. Vi Thi Mai Lan, to Columbia University for a month-long training visit in the lab of Dr. Benjamin Bostick. The exact schedule for the visit is still being worked out, but it should be completed by the time this project expires at the end of December 2016.