Modeling-Oriented Geochemical Monitoring for Complex Subsurface Matrices

Statement of the problem or situation that is being addressed. Complex subsurface systems are substrates for natural, disturbed, and managed terrestrial vegetation systems. Reactive transport models have become popular tools for predicting geochemical and biogeochemical processes in these complex subsurface matrixes, including the vadose zone and groundwater, but their accuracy and predictive power are limited by our capability to collect chemical information from the field. Advanced, in-situ sensing systems for cost-effectively accurate relevant information about nutrients and other chemicals in the soil and saturated zone are needed in order to realize the full capability of these computational tools, and to properly characterize subsurface systems. Statement of how this problem is being addressed. We propose to develop a stand-alone in-situ system for continuous monitoring of carbon and nitrogen compounds in the vadose zone and groundwater. Specifically, this system will collect information in real- time about key geochemical parameters, so that reactive transport models can simulate biogeochemical processes in complex subsurface matrices. The proposed monitoring system will incorporate our unique intrinsic fiber optic sensors, capable of covering large areas, connected to a compact unattended optoelectronic unit capable of reporting spatially averaged measurements of oxygen, carbon dioxide, nitrates, and/or Fe2+ and Fe3+, which are key parameters for understanding interactions among gases, water, microbes, and rock soils across spatial scales. The proposed project will be based on our proprietary distributed intrinsic optical sensor technology for monitoring carbon dioxide leaks in carbon capture and storage. The first generation prototype of this sensor has already been validated in the field. What is to be done in Phase I? In Phase I we will fabricate a three-parameter sensor cable to monitor CO2, nitrates, and temperature, and characterize its response to target soil and groundwater properties in the laboratory. Initial field tests will demonstrate the potential of the technology to operate outside a controlled laboratory environment. In Phase II we will construct a complete, compact, autonomous system for long-term deployment and wireless reporting of multiple soil and groundwater properties. After laboratory characterization, the system will be validated in the field by comparison with classical monitoring techniques. Field data from the sensor system and analysis of the biomass at the field site will populate reactive transport models in order to study biological processes and interactions between saturated and unsaturated zones. Commercial Applications and Other Benefits An economical and uncomplicated system for measuring the properties of a soil and its interaction with groundwater over extended areas will directly benefit climate science, and it will also have commercial applications in agriculture and civil engineering. The market for wireless sensors for environmental and agricultural monitoring is expected to approach $3B by 2016, at an estimated compound annual growth rate of 11.2% from 2011 to 2016. Physical sensors are relatively mature holding the largest share with 40%; chemical and mechanical sensors follow second and third, with shares of 37% and 22%, respectively. Key Words nitrate, carbon dioxide, optical fiber, sensor, reactive, transport, groundwater, vadose Summary for Members of Congress: We will develop a system for stand-alone, in-situ, continuous monitoring of carbon and nitrogen compounds in the vadose zone and groundwater over extended areas, which will directly benefit climate science, and will also have commercial applications in agriculture and civil engineering.