RAPID: Toward anIimproved Understanding of Reactive Organic Carbon Sources and Arsenic Mobility in Reducing Aquifers

San Diego State University Foundation, San Diego CA

Investigators

Abstract

CBET-1449247 Mladenov RAPID: Toward an improved understanding of reactive organic carbon sources and arsenic mobility in reducing aquifers Arsenic is a world-wide issue in groundwater when used as a source of drinking water. A study in 2007 suggests that over 137 million people in more than 70 countries, including the United States, are affected by this poison. A challenge is to better understand the chemistry of arsenic in groundwater in order to inform engineering decisions in treating that water to make is safe for drinking. One of the important considerations is the presence of dissolved organic matter, often referred to as DOM. There is some controversy over the source of this DOM, as to whether it is the result of the discharge of wastewater or is from natural sources. Both are possible; however it appears that in most cases it is naturally occurring organic matter that is present in the ground waters. In turn, this DOM can react naturally with microorganisms, which in turn can affect the chemistry of the arsenic. The challenge of identifying the sources of reactive organic carbon (DOM) driving microbial reduction continues to limit our ability to predict the distribution of arsenic in reducing aquifers. The proposed research is a concerted effort to correlate analytical methods for dissolved organic matter (DOM) characterization and reactivity to fluorescence spectral acquisition of DOM collected from uncompromised sediment pore-water. This will provide new information about the potential and limits of fluorescence spectroscopy for characterizing DOM in reducing environments that often have high metal content. In addition, via this coordinated drilling effort at sites with and without large-scale pumping, DOM chemical characterization and large volume sampling for radiocarbon dating will test the hypothesis that, in the absence of massive irrigation pumping, sediments may provide labile DOM to drive microbial reductive dissolution of arsenic. Samples will be collected and analyzed to provide key information regarding DOM source and age under scenarios that are generalizable to other aquifers. With the unique freeze-shoe sampling technology and availability of a mobile laboratory, this effort will allow for the optimization of techniques appropriate for large volume sampling, uncompromised pore-water sampling, and rapid DOM characterization. The proposed research takes advantage of multiple datasets being collected by scientists and students from 16 different countries in the summer of 2014. The drilling effort utilizes novel freeze-shoe sampling technology to collect uncompromised sediments and adjacent pore-waters from the arsenic-containing Mahomet Aquifer (Illinois) for immediate analysis at a mobile laboratory at the site. The proposed RAPID project will support sample collection at the Mahomet Aquifer field site and preparation of samples for radiocarbon dating and determinations of proteins, carbohydrates, and fulvic acids. The next large sampling similar to this will not be for three years.