To gain valuable insight into the groundwater flow near Red Hill, Oʻahu, researchers at the University of Hawaiʻi at Mānoa began a dye tracer study in February. Using a method that has been approved by the U.S. Environmental Protection Agency and the Hawaiʻi Department of Health, the team injected a fluorescent compound to a monitoring well and will study its migration through the aquifer over the spring of 2025.
Following the jet fuel leaks from storage tanks in 2014 and 2021, there has been significant concern from community members and scientists about the safety of drinking water in the area. After the 2021 release of jet fuels, water pumped from Red Hill Shaft no longer supplies public drinking water but rather is entirely discharged to Halawa Stream as part of ongoing recovery efforts at the request of regulators.
Recent geophysical and hydrological studies have begun to provide a better understanding of the regional geology and groundwater flow rates and directions. The dye tracer study will validate those findings and provide data sets to inform current and future modeling efforts. Rhodamine water tracer (WT) was selected for this study because it is non-toxic, straightforward to measure, breaks down in sunlight, doesn’t bind to soils and washes away easily.
“Fluorescent dyes, such fluorescein and rhodamine, have been used for decades by the U.S. Geological Survey to understand river dynamics and were safely used to study the groundwater migration of freshwater discharge off the coast of Lahaina, Maui in 2011,” said Toomas Parratt, researcher in the Hawaiʻi Institute of Geophysics and Planetology at the UH Mānoa School of Ocean and Earth Science and Technology and lead hydrogeologist on the study.
The team injected dye into RHMW08, a quarter of a mile upgradient from Red Hill Shaft (RHS), which was shut down as a public drinking water supply following the November 2021 fuel leak. However, extraction at RHS is still ongoing with a granular activated carbon treatment system prior to discharge to Halawa Stream. For the tracer study the water extraction rate was temporarily increased to over 4 million gallons per day, consistent with the permitted rate, to maximize the recovery of the injected dye.
The water pumped from RHS will be monitored every 10 minutes to determine the concentrations of the tracer dye in the extracted water. The arrival time of the dye at RHS and the total mass captured by RHS’ pump will allow for the estimation of groundwater velocities and the efficacy of dye recovery. The concentration of dye will also be monitored after treatment by the Navy’s activated charcoal filters to ensure adequate dye removal prior to discharge to Halawa Stream, since it is disconnected from the public drinking supply.
“From the ongoing hydrogeological studies the majority of the dye is expected to be captured by RHS and will not discharge to any surface water bodies, including streams, springs and near-shore seeps since the dye was injected below sea level within the capture zone of RHS,” Parratt emphasized.
Additional information
Preliminary results from the dye tracer study will be shared publicly in summer 2025.
An informational webinar about the tracer study can be accessed here and future webinars will be posted here. For more information, visit the Red Hill Dye Tracer Study FAQ or contact Parratt at toom@hawaii.edu with questions.
