Water Resources Research Act Program

Details for Project ID 2020GU271B

Development of the Groundwater Model of the Yigo-Tumon Basin, Northern Guam Lens Aquifer

Institute: Guam
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $14,387 Total Non-Federal Funds: Not available

Principal Investigators: Dr. Nathan Habana

Abstract: Guam has plans for major island growth and expansion well within the next 10 years, requiring more water from its principal source—the Northern Guam Lens Aquifer (NGLA). Developers will be looking for groundwater models to test aquifer capacity and placement of additional wells. Reliable groundwater models are very useful for determining aquifer development strategies that include optimum production well configuration and sustainable management of water resource. The Yigo-Tumon Basin, in the NGLA, is the most abundant source of utility water out of the 6 aquifer basins, where deep production wells extract about half of the total 42 MGD from the NGLA, which is about 90% of total water produced on the island. More than 20 years of NGLA research and data is available that can be used to develop a reliable groundwater model of the NGLA, starting with the Yigo-Tumon Basin. A new addition to NGLA research in 2019 is the time-series of phreatic profiles in three deep observation wells in this basin that present the spatially varied dynamic response to recharge, from which model results can be matched. And most recently accomplished, groundwater model assessment of the capacity of each basin’s “sweet spot,†the parabasal zone. Also, the advancement in groundwater modeling software and computer technology, integrating tested finite element code extensions (FEM Water), GIS capability, 3-D interface are available in Aquaveo® Groundwater Modeling Systems (GMS) that will be the selected model application, and that will run on WERI’s fast computer. Methods: The principal investigators will continue to lead a research team composed of themselves, a WERI-based graduate research assistant, working in collaboration with colleagues at Brigham Young University, and Aquaveo Technical Support to develop an upgraded groundwater model. This will require preparation and assembly of the data sets; consider latest collection of climatic phenomena and geologic features that are most likely to exert significant rainfall amount and intensity, infiltration rates, aquifer storage, groundwater flow, and groundwater salinity on northern Guam; and apply statistical, geospatial, and other analytical tools to identify, characterize, and interpret past and present spatial patterns in rainfall, groundwater levels, specific conductivity, chloride concentrations, and production rates from existing wells within the NGLA. The team will recalibrate and test the model to existing, new observation wells, and rehabilitated observation wells.Objectives: This project will accomplish these objectives:(1)Data acquisition and literature review of published and emerging research on spatial and temporal distributions and trends of rainfall and salinity in the NGLA(2)Assemble the model, considering groundwater boundary conditions, spatial and temporal parameters, and wells(3)Run scenarios and simulations to test the model(4)Collaborate with colleagues, demonstrating performance, considering modifications, critique, improvements, and refinements, and accessing software technical support(5)Recommend the availability and usefulness of the new model to stake holders in major island development