The document summarizes a study that aimed to estimate inventories and fluxes of the herbicide glyphosate in the Faga`alu watershed in American Samoa. Key points: 1) Fieldwork was conducted to collect water samples from wells, springs, streams and groundwater to test for glyphosate and other contaminant concentrations. 2) Samples were analyzed in a lab at UH Manoa, with low levels of glyphosate found. 3) A hydrological model was created using GIS and groundwater modeling programs to identify potential transport pathways and contamination sources. The model suggests sources may originate under developed urban areas.

1. Groundwater modeling of pesticide
fluxes in the Faga`alu Watershed,
American Samoa
By Eric Welch, Global Environmental Science,
SOEST
Mentor: Dr. Henrietta Dulai

2. Introduction
Objective
Estimate inventories and fluxes of the herbicide
glyphosate in the Faga`alu watershed.
Why do this?
1. To determine if levels of concern are present by
direct sampling and measurement of surface and
groundwater.
2. To identify source regions by determining transport
pathways in aquifer’s groundwater by a hydrological
model and matching to land-use by GIS spatial
analysis.

4. Introduction
Faga`alu Watershed
 2.5 km2 watershed
 Forested slopes
 Densely populated alluvial plain
 Faga`alu Stream drains to ocean
Mt. Matafao1
Faga`alu Quarry2
Agricultural LandFaga`alu Watershed on the inner Pago

5. Introduction
Drinking water and contamination
 90% of American Samoa’s drinking water supply
comes from groundwater
 Anthropogenic groundwater pollutants:
◦ Pesticides
◦ Pathogens
◦ Excess Nutrients
 Inadequate agricultural
techniques can leach
contaminants into aquifer
Contaminant pathways into the
groundwater system. 3

6. Introduction
What is Glyphosate?
Glyphosate (aka “Roundup”)
 Most Popular Herbicide Worldwide
 Used on: Crops, Roadsides, Lawns,
Forests, Gardens
Various Roundup/
Glyphosate products
at Tutuila’s ACE
Hardware.
Fields being sprayed with herbicide to control weed
growth.4

7. Methods
Fieldwork in American Samoa
(August 2016)
•Collected Water Samples
for
Pesticide Concentration
•From the Faga`alu
watershed
sampled:
1 Well
2 Coastal Springs
2 Tributaries
7 Main Stream Locations
7 Base Flow
3 High Flow
3 Stream Bank Groundwater
Educating Samoan children as
they helped collect water samples.
Ditch portion of the lower Faga`alu
Stream.

8. Methods
Sample Analysis and Labwork at UH Manoa
•Also tested for:
•Nutrients, Ions, D&O, Salinity,
Conductivity, DO%, Radon
•Tested for concentrations of
herbicide glyphosate using
an
ELISA Method
Measuring Equipment used to analyze samples. 5, 6, 7
Dr. Dulai and myself running glyphosate tests in lab.

9. Methods
GIS and Groundwater Modeling
Used ArcGIS to:
•Spatial analysis of
glyphosate
concentrations
in watershed.
Used GMS to:
•Create hydrological
model
using USGS
MODFLOW
and MODPATH
modeling
programsWorking on ArcGIS, mapping glyphosate
distribution.
Modeling the Faga`alu Aquifer with GMS.
9
8

10. •Gaining stream reaches
had elevated 222Rn levels
and losing stream
reaches had lower levels,
confirming groundwater
input.
Results
Base flow and
Radon
1
10
100
1000
0 500 1000 1500
222RnConcentration(dpm/L)
Distance Upstream (m)
Faga`alu Radon Levels
1
2
3 4
5
6
7
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0 500 1000 1500
StreamFlow(m3/s)
Distance Upstream (m)
Faga`alu Base Flow
Gaining Losing
1
2
3 4
5
6 7
Base flow discharge values for Faga`alu
stream
Rn-222 Levels in Faga`alu Stream (yellow
stars represent streambank groundwater
samples)
The Faga`alu Watershed with
sampling locations marked.
Faga`alu
watershed

11. Faga`aluFaga`alu

12. Results
Glyphosate
Concentrations 0
0.05
0.1
0.15
0.2
0.25
0.3
0 500 1000 1500
Concentration(ppb)
Distance Upstream (m)
Fagaalu Glyphosate Concentrations
Stream- Low Flow
Stream- High Flow
Stream- Tributaries
Groundwater Samples
Glyphosate concentrations from sampling locations in
Faga`alu by sample-type , mapped with land use data.
Glyphosate levels at low-flow and high-flow
stream conditions, and tributary and
groundwater samples.

13. Results Hydrological Model
Groundwater flow paths to
wells, coastal springs, and
stream bank groundwater
locations were modeled.
Computed vs. Observed water table values
for calibrated hydrological model.
Water table levels were
calibrated using base
flow discharge data
along with well and
spring levels in the
Faga`alu watershed.
Water
Level

14. Discussion / Conclusion
 Glyphosate concentrations in Faga`alu watershed
are low, however transport through groundwater is
evident.
 Elevated pesticide levels correlate with shorter flow
paths, suggesting that relative proximity to
glyphosate sources may be an important factor in
contamination.
 The hydrological model points to sources of
contamination that originate under developed urban
areas. I am looking for a better ‘land use’ map that
has all agricultural lands present in the watershed.

15. Acknowledgements
I would like to give big thanks to:
 UROP for the funding and supporting me
 Dr. Henrietta Dulai and Dr. Aly El-Kadi for their
guidance and mentorship through this project
 Christopher Shuler for his help in my fieldwork in
Samoa and advice and direction this past year
 Dr. Michael Guidry (GES Chair) always great
guidance
 Others who helped along the way: Olkeba Tolessa
Leta, my Samoa Crew (Daniel Amato, Veronica
Gibson, Nalani Olguin), employees from ASPA,
AS-EPA, ASCC, and NASDA in American Samoa,
Dr. Thomas Shea for the GIS skills, UH Manoa GG
Department, all my SOEST professors &
classmates for their encouragement

16. References
Dulaiova, Henrietta, R. Camilli, P. B. Henderson, and M. A. Charette. "Coupled Radon,
Methane and Nitrate Sensors for Large-scale Assessment of Groundwater Discharge
and Non-point Source Pollution to Coastal Waters.“ Journal of Environmental
Radioactivity 101.7 (2010): 553-63.
Glyphosate ELISA Microtiter Plate: Instruction Manual. Abraxis Inc. Warminster, PA. E-
mail: info@abraxiskits.com.
Izuka, Scot K., J.A. Perrault, and T. K. Presley. "Areas Contributing Recharge to Wells in
the Tafuna-Leone Plain, Tutuila, American Samoa." USGS Scientific Investigations
Report 2007-5167 (2007).
Messina, A.M., and T.W. Biggs. "Contributions of Human Activities to Suspended Sediment
Yield during Storm Events from a Small, Steep, Tropical Watershed.“ Journal of
Hydrology 538 (2016): 726-42.
Paul, Vijay, and R. Pandey. "Is the Herbicide Glyphosate Really Safe?" Current Science
112.1 (2017): p. 11-13.
Shuler, Christopher K. (2016). “Source partitioning of anthropogenic groundwater nitrogen
in a mixed-use landscape, Tutuila, American Samoa” (Masters diss.). University of
Hawai`i at Manoa.
Pictures from:
1- http://www.terragalleria.com/pacific/american-samoa/pago-pago/picture.samo3890.html
2- http://www.ecosailingcharters.com/2012/12/lbj-waterfall-hike-american-samoa.html
3- https://pubs.usgs.gov/fs/2005/3087/
4- https://www.thermofisher.com/blog/proteomics/pesticides-in-ambient-air-a-novel-lc-hrms-
protocol/
5- https://www.ysi.com/6920-v2-2
6- http://www.durridge.co.uk/products_rad_h2o.shtml
7- http://www.abraxiskits.com/products/readers/
8- http://www.esri.com/arcgis/about-arcgis
9- http://www.aquaveo.com/software/gms-groundwater-modeling-system-introduction

17. Questions?
before after
Pesticide-free agriculture Heavy pesticide-use in agriculture