Groundwater Development Potential and Conceptual Hydrogeologic Model for Tutuila, American Samoa.

Shuler, C.K., El-Kadi, A.I., and Eyre, P.R. (2018). - WRRC technical report. (2019)

In this report, currently available hydrological information was compiled with recently acquired subsurface datasets to inform an updated conceptual hydrogeological model of Tutuila’s groundwater and surface water resources. Published reports, recently collected data, and studies from similar basaltic islands were integrated to explain groundwater behavior in Tutuila’s already developed basal aquifers, and to inform hypotheses of high-level groundwater occurrence where data limitations exist. Datasets presented include borehole, geophysical, water level, aquifer test, geomorphologic, and surface water data. This information is a key component to management of the island's limited drinking water resources and provides the foundation for the development of numerical models.

Includes an associated 8 page Management Summary (download) that summarizes the report content!

Groundwater Recharge for Tutuila, American Samoa Under Current and Projected Climate as Estimated with SWB2, a Soil Water Balance Model

Shuler, C.K. and El-Kadi, A.I. (2018). - WRRC Special Report . (2018)

We applied a water budget approach using SWB2, a soil water-balance model, to develop a water budget model for the entire island of Tutuila in American Samoa. The model provides high-resolution groundwater recharge estimates. This information is essential for assessing water resources availability on islands such as Tutuila where groundwater makes up the majority of drinking and municipal water supplies. Other water budget components such as evapotranspiration, canopy interception, runoff, and mountain front recharge were also quantified with the SWB2 model for average present-day climate conditions. Additionally, the potential effects of future climate change on water resources availability were simulated by integrating dynamically downscaled climate predictions for 2080 to 2099 derived from externally supplied global climate model results. Climate scenarios suggested an increase in net-infiltration of 17 to 27% may be expected by the end of the century depending on the emissions scenario used.

Includes an associated 7 page Management Summary (download) that summarizes the report content!

UH-WRRC – ASPA Hydrological Monitoring Network Handbook.

Shuler, C.K. and El-Kadi, A.I. (2018). - WRRC Special Report . (2018)

Our research group at the UH Water Resources Research Center and the territory’s sole water utility, the American Samoa Power Authority initiated a cooperative agreement for the purpose of developing a new weather station, stream gauging, and aquifer monitoring network. This report provides locations, descriptions, and care and maintenance recommendations for each of the 21 instruments in the ASPA-WRRC monitoring network as of August 2017. Each section provides an overview of the equipment used for the current iteration of the network, and each site is described to ensure that details about site access and particularities are documented.

Includes an associated 3 page Management Summary (download) that summarizes the report content!

Provisional Hydrogeologic Data and Recommendations for Sustainable Groundwater Management, Tutuila American Samoa.

Shuler, C.K. and El-Kadi, A.I. (2018). - WRRC Special Report . (2018)

This report provides water managers with important groundwater information and management recommendations that currently represent the state of current efforts towards determining rates of sustainable yield for Tutuila, American Samoa. Interim management recommendations based on these data are presented, and existing data gaps in the progress towards the goal of sustainability are identified. A majority of the information presented in this report is focused on preparation of the development of water budget and numerical groundwater models that can then be applied to assess sustainable yield scenarios, once a comprehensive process to determine these criteria is undertaken.

Includes an associated 7 page Management Summary (download) that summarizes the report content!

Groundwater Development Potential & Exploratory Drilling Recommendations Tutuila, American Samoa

Shuler, C.K. Paul Eyre, and El-Kadi, A.I. (2018). - WRRC Special Report . (2018)

This report presents a framework for recommending locations for exploratory drilling that target new sources of groundwater in both high-level and basal aquifers, including:

- Compilation of existing hydrogeologic knowledge

- Application of geologic principles to estimate subsurface conditions

- Prioritize exploration regions or watersheds based on available data and information

Includes an associated 4 page Management Summary (download) that summarizes the report content!

Island Wide Nutrient Modeling and Quantification of Coastal Freshwater Discharge for Tutuila, American Samoa.

Shuler, C.K. Prepared for: American Samoa Environmental Protection Agency (2019)

Includes an associated 8 page Management Summary (download) that summarizes the report content!

American Samoa Water Use Data: A Workplan for Evaluation and Improvement

Shuler, C.K. & Eyre, P. Prepared for: American Samoa Power Authority (2018)

The primary purpose of this document, The American Samoa Water-Use Workplan, is to assess the current state of water-use information in the territory of American Samoa. This includes territory-wide water-use data such as withdrawals from surface and groundwater sources, water delivery information organized by category of use, return flows back to the environment, and ancillary information including water source, salinity, or populations served. This report not only presents information about data availability in American Samoa, but also how data are stored, how data are communicated, and the feasibility of sharing data in their current formats.

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

CK Shuler, DW Amato, V Veronica Gibson, L Baker… - Hydrology (2019)

Anthropogenic nutrient loading is recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ¹⁵N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ¹⁵N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed.

Isotopes, Microbes, and Turbidity: A Multi‐Tracer Approach to Understanding Recharge Dynamics and Groundwater Contamination in a Basaltic Island Aquifer

Shuler, C. K., Dulai, H., DeWees, R., Kirs, M.... Groundwater Monitoring & Remediation (2019).

Wells designated as groundwater under the direct influence (GUDI) of surface water have caused an ongoing boil‐water advisory afflicting the island of Tutuila, American Samoa for almost a decade. Testing shows contamination correlates with heavy rainfall events, however, the mechanism of this contamination has remained unknown. Surface water may reach wells through improperly sealed well casings, or through the aquifer matrix itself. In this study, we used three independent surface water tracers, turbidity, indicator bacteria, and water isotopes were used to assess recharge timing and determine contamination mechanisms. Results indicate subsurface flow occurs through highly permeable aquifer materials. This knowledge supports local management decisions and shows that repairing or replacing wells will likely result in continued contamination.

Source partitioning of anthropogenic groundwater nitrogen in a mixed-use landscape, Tutuila, American Samoa

CK Shuler, AI El-Kadi, H Dulai, CR Glenn, J Fackrell. Hydrogeology Journal (2017)

This study presents a modeling framework for quantifying human impacts and for partitioning the sources of contamination related to water quality in the mixed-use landscape of a small tropical volcanic island, Tutuila, the main island of American Samoa. Tutuila has three predominant anthropogenic non-point-groundwater-pollution sources of concern: on-site disposal systems (OSDS), agricultural chemicals, and pig manure. The approach utilizes a numerical groundwater flow model, a nitrogen-loading model, and a multi-species contaminant transport model. Model results are calibrated and validated with dissolved groundwater TN concentrations and inorganic δ¹⁵N values, respectively. Results indicate that OSDS contribute significantly more TN to Tutuila’s aquifers than other sources, and thus should be prioritized in future water-quality management efforts.

Metal mobilization as an effect of anthropogenic contamination in groundwater aquifers in Tutuila, American Samoa

Okuhata, B. K., Dulai, H., Shuler, C. K., Fackrell, J. K., & El-Kadi, A. I. Water (2020)

The remineralization of anthropogenically sourced organic matter produces nitrate and dissolved inorganic carbon, which, according to previously published studies, have the potential to mobilize naturally occurring metals. This study provides further evidence that nutrients and dissolved inorganic carbon, along with naturally sourced metal concentrations, become elevated along pollution gradients and show correlation with each other.

Rainwater harvesting in American Samoa: current practices and indicative health risks.

Kirs, M., Moravcik, P..... Shuler, CK... & Ahmed, W. (2017).Environmental Science and Pollution Research

The aim of this pilot-scale study was to investigate current RHRW practices in American Samoa and to evaluate and compare the quality of water from common potable water sources including RHRW stored in tanks, untreated stream water, untreated municipal well water, and treated municipal tap water samples. Samples were analyzed using culture-based methods, quantitative polymerase chain reaction (qPCR), and 16S amplicon sequencing-based methods.

Submarine groundwater discharge and stream baseflow sustain pesticide and nutrient fluxes in Faga’alu Bay, American Samoa.

Welch, E. M., Dulai, H., El-Kadi, A., & Shuler, C. (2019). Frontiers in Environmental Science

This study seeks to demonstrate the importance of groundwater flow for the distribution and transport of selected pesticides and nutrients in the Faga'alu aquifer on the island of Tutuila in American Samoa. Field measurements, including seepage runs and analysis of stream and groundwater for pesticides and nutrients, were combined with hydrological modeling. Selected analytes were glyphosate (GLY), dichlorodiphenyl-trichloroethane (DDT), imidacloprid, and azoxystrobin for pesticides and chemical species of nitrogen, phosphate, and silicate for nutrients.