This SBIR Phase II research proposal aims to develop a commercial multi-Coil Magnetic Resonance Sounding (MRS) system for 3-D groundwater imaging and characterization. The principal innovations are the use of multi-coil arrays and the development of coherent signal processing methods to reconstruct 3-D images. The feasibility of this system concept through computer simulation, analysis, and by acquiring experimental (very low SNR) multi-coil NMR data has been established. It is now proposed to design and assemble a field-scale multi-coil MRS prototype instrument with surface coil diameters on the order of 50-100 meters, and to field test this prototype extensively with the U.S. Geological Survey and a groundwater -consulting firm. This multi-coil MRS system enables a critical performance improvement in the area of spatial resolution (3-D vs. 1-D) and at least an order of magnitude improvement in sensitivity (effective SNR).<br/><br/>Inadequate access to clean, safe, and reliable sources of drinking water is a primary cause of disease in the developing world. Inadequate access to groundwater resources, and inadequate understanding of the long-term effects of groundwater use, pose fundamental limitations on economic and agricultural development in much of the developed world, including the United States. As an inexpensive, low-energy, and non-invasive groundwater exploration method, the proposed technology could have significant positive impacts on world health, natural resource management, and economic development.