Water Resources Research Act Program

Principal Investigators: Joseph Rouse

Abstract: The Northern Guam Lens Aquifer (NGLA) is Guam’s primary source of freshwater for potable use. This porous limestone formation currently provides approximately 80% of the island’s municipal water supply. Aggressive production of groundwater has grown to 40 million gallons per day (mgd). 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 contaminants from anthropogenic sources are showing up in the NGLA. Much more baseline data of contaminant concentrations are needed to determine if the problem is greater in zones with sewer collection lines, or in zones that rely on household septic tanks; furthermore, it is not known if contaminant levels are increasing, or not. It is essential that these issues be studied before actions are taken to extend sewer collection lines or even build new wastewater treatment plants in Northern Guam. In addition, the effectiveness of septic tanks is also an issue of concern. As an alternative to traditional septic tanks, consideration is increasingly given to use of single-family prefabricated, packaged treatment units. It is considered that these units could serve to reduce the potential of contamination reaching the water table. This proposal responds to the critical needs expressed at the Advisory Council Meeting 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, etc. with respect to time and location. In addition, it addresses the need for evaluation of innovative wastewater treatment units as alternatives to conventional septic tanks for individual homes, commercial buildings, or hotels. Methods: Data collection will be done first on selected production wells at representative locations. WERI Technical Report #95 has a map of wells of nitrate trend analysis. Selection criteria include production wells near sewered areas, non-sewered areas, and a combination of both sewered and non-sewered. Multi-probe meters (YSI Inc., Professional Plus) will be used at the selected sites to measure nitrate-N, ammonium-N, pH, temperature, and possibly ORP, atmospheric pressure, conductivity, etc. Data will be imported to a computer for a multi-variate time-series analysis and mapping development. Objectives: The objectives of this project are: (1) Review of the literature addressing wastewater-N and groundwater-N cycle transformation triggers, and study of groundwater contaminant transport. (2) Analysis of spatial time-series wastewater-N data at sites with rainfall and other possible influences such as pH, ORP, sewage discharge events, etc. (3) Translation/interpretation of analysis such as increasing/decreasing trends, averages, and spatial distribution. (4) Assist in the development of strategies to improve wastewater management on Guam.