Hydrogeologic Survey of Santa Rita Spring, Guam: Determination of Its Natural Capacity and Development Options
Hydrogeologic Survey of Santa Rita Spring, Guam: Determination of Its Natural Capacity and Development Options
Presented on Tuesday, December 3, 2019
Santa Rita Spring discharges fresh water from a hillside above the village of Santa Rita (pop. 7,500) in southwest Guam, and contributes to the village's municipal water system. It is a perennial karst spring that forms at the contact between a Miocene limestone aquifer capping Eocene-Oligocene volcaniclastic strata on the cuesta that forms the southwest edge of the island. The spring forms within a 30-ft-thick inter-bedded, depositionally-transitional unit mapped as the basal member of the overlying limestone. An impoundment was built by the U.S. Navy in 1929 and is still in service, producing up to 450 gpm. However, the persistence of wet ground, puddles, and piping around the structure, especially during wet weather, indicates the impoundment captures only part of the natural discharge. Past attempts to intercept the uncaptured water by modifying the existing structure were unsuccessful. This project undertook a comprehensive hydrogeological study of the spring and its watershed to determine the distribution of the discharge from within the complex contact, evaluate the spring’s full potential capacity and responsiveness to recharge, and recommend economical options for capturing the entire flow. Investigation of the contact at other locations confirmed the presence of multiple distributary conduits along the contact horizon. A 3-dimensional model of the spring’s upland watershed was developed using previous electromagnetic survey data and current geospatial analysis tools. Watershed rainfall and spring discharge measurements showed the spring’s potential capacity to be 200 to 1,200 gpm. Eleven boreholes were drilled at the site, from 30 to 90 feet deep. Cuttings were collected to characterize stratigraphy, and piezometers were installed to characterize site hydraulics from pump and slug tests of the impoundment. The new understanding of site hydrogeology provides the basis for design recommendations that will efficiently capture the entire capacity of the spring.
Paul Bourke
Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Paul Bourke is a graduate student pursuing an MSc degree in Environmental Science at the Water & Environmental Research Institute (WERI) at the University of Guam (UOG). For his thesis, he is researching the development of the Santa Rita Spring, this project is funded by the Guam Water Authority (GWA). He has a Bachelors Degree in Civil Engineering from the Cork Institute of Technology, 2005 and a BSc in Economics from Boston College, 2001.
Paul was born and raised in Ireland. Upon the completion of his MSc in Environmental Science, Paul hopes to peruse a career in water resources management and engineering. Paul enjoys football(soccer), surfing, and spending time with his family.
John Jenson, PhD
Water & Environmental Research Institute of the Western Pacific, University of Guam
Dr Jenson is Professor of Groundwater Hydrology, and Director of the University of Guam's Water & Environmental Research Institute of the Western Pacific (WERI). His current research interests include development of the Carbonate Island Karst Model and its application to numerical modeling and sustainable management of island karst aquifers.
Nathan Habana, PhD
Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Dr Habana is Assistant Professor of Groundwater Hydrology at the University of Guam's Water & Environmental Research Institute of the Western Pacific (WERI). His duties at WERI include serving as Coordinator for the Guam Hydrologic Survey Program, which compiles and analyzes basic data on Guam’s freshwater resources. His current research interests include modeling of vadose and phreatic transport, and the management of salinity and nitrate contamination in island aquifers.
Mark Lander, PhD
Water & Environmental Research Institute of the Western Pacific, University of Guam, Mangilao, Guam
Dr. Lander is a tropical meteorologist with expertise in tropical weather, tropical climate, typhoon forecasting and prediction, climate variability and climate change, and the ENSO phenomenon. His research efforts include field work on Guam and across the Micronesia region, and operational forecasting of seasonal typhoon risk and ENSO-related drought. Dr. Lander is active in the international community, and has given lectures on tropical climate and typhoon behavior at venues in Thailand, Australia, Fiji, Majuro, Pohnpei, Oman, Hong Kong, Hawaii and China. He also teaches graduate-level courses in the University of Guam’s Environmental Science program.