T369 Hydrogeology of Island Environments in a Changing Climate (Posters)

Wednesday, 25 October 2017
9:00 AM - 6:30 PM
Halls 4EF

AN ISOTOPIC AND MICROBIOLOGICAL MULTI-TRACER APPROACH TO ASSESSING RECHARGE MECHANISMS IN SURFACE WATER AFFECTED WELLS ON TUTUILA, AMERICAN SAMOA

Paper number: T369-1
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

On Tutuila Island, in the Territory of American Samoa, the municipal water supply system is currently unable to provide potable drinking water to the island’s growing population. In 2009, a boil-water advisory was issued throughout much of Tutuila’s water service area due to elevated turbidity and Escherichia coli detections in supply wells from the island’s most productive aquifers located below the Tafuna-Leone Plain. The affected wells are designated by the U.S. Environmental Protection Agency as groundwater under the direct influence (GUDI) of surface water, and federal drinking water quality standards require a cost-prohibitive level of treatment for their water to be potable. Although it is clear that surface water is infiltrating certain wells on Tutuila, the mechanism of this rapid recharge remains unknown. This study’s objective is to develop a better understanding of recharge mechanisms and timescales by collecting and analyzing data from geochemical and isotopic tracers, physical aquifer parameters, and bacteriological indicators. Methods include assessing temporal variation in δ2H and δ18O values in precipitation and groundwater, using microbial indicators and cosmogenic isotopes to assess aquifer material properties, and assessing physical aquifer response to rain events. Monthly sampling of water isotopes in precipitation has shown distinct trends in seasonality, whereas groundwater samples lack this trend, indicating that significant flushing of these aquifers does not occur on a seasonal basis. Bacteriological sampling shows a significant difference between non-GUDI wells and GUDI wells that consistently test positive for Total Coliform and E. coli, indicating that filtration ability of the GUDI aquifers is low. Results of this study are intended to inform development of Tutuila’s future water resources, which depends on a clear understanding of the hydrogeological dynamics of the Tafuna and Leone Aquifers.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-297974

© Copyright 2017 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.