Water Resources Research Act Program

Details for Project ID 2020GU269B

Production well nitrate-N trends in the Northern Guam Lens Aquifer

Institute: Guam
Year Established: 2020 Start Date: 2020-03-01 End Date: 2021-02-28
Total Federal Funds: $27,745 Total Non-Federal Funds: Not available

Principal Investigators: Dr. Nathan Habana

Abstract: Increased development of uncontrolled sewage transport and poor treatment over an aquifer is a threat to the quality of the water source. The Northern Guam Lens Aquifer (NGLA) is Guam’s primary source of potable freshwater, for which the economical access has most of the population and activities developed right above it. This porous limestone formation currently provides approximately 90% of the island’s municipal water supply. With water demand rising and concerns over water quality increasing, proper management of this freshwater source has become critical to the welfare of the island’s increasing population of residents and tourists. Preliminary inquiries have suggested that wastewaters are appearing in production wells. Development over the aquifer has overwhelmed the connection into sewer mains and effectiveness of septic tanks is also an issue of concern. Nitrate-N concentration in utility water is one of the indicators that suggests severity of wastewater contaminant levels. Nitrate-N data from 1978 to current is available for nearly all production wells on Guam from which a trend analysis may provide spatial and temporal baseline information. WERI Technical Report 95, 2001, had done a trend analysis on production well nitrate-N. Nearly 20 years since, Guam has increased in development. This analysis will update and expand on the method used to compare and assess the time-series nitrate trends seen in all the production wells, to include examination of the surrounding development and the sources of wastewater discharge. The results will also be preparatory for the use of wastewater solute transport modeling of the aquifer that will be used to refine current wastewater regulations.This proposal responds to the critical needs expressed at the Guam Advisory Council Meetings, the interagency Groundwater Resources Development and Technical Experts Group, the Legislature, and Guam EPA to conduct research on spatial and temporal trends in levels of contaminants in Guam’s groundwater, as well as the need for continuous baseline studies on levels of nitrogenous compounds, with respect to time and location.Methods: Data trend analysis and mapping of results will provide temporal and spatial solutions. A complete data nitrate-N analysis includes regression, r-critical, data spread, and ranking. The results will be mapped with wastewater sources, septic and sewer lines, onto a backdrop—the published Northern Guam Lens Aquifer map.Objectives: The objectives to complete the project are:(1) Review of the literature addressing wastewater-N and groundwater-N cycle transformation triggers, and study of groundwater contaminant transport.(2) Select appropriate Nitrate-N data analysis for observing trends, spread, and rank.(3) Translation/interpretation of analysis such as increasing/decreasing trends, averages, spread and spatial distribution.(4) Map results and preliminary model analysis as a summary(5) Recommend development strategies to improve wastewater management on Guam.