How does EPA know that Polycyclic Aromatic Hydrocarbon (PAH) detections at ʻAiea Wells are not related to any/all historic Red Hill fuel spills?
EPA evaluated the available data from the Honolulu Board of Water Supply (BWS) and the Navy and we have concluded that Red Hill is an unlikely source for the following reasons:
Groundwater Testing Results
EPA is pleased to present an application developed to provide you with a simple way to view up-to date information about groundwater quality around the Red Hill Bulk Fuel Storage Facility in Hawaiʻi. Learn more at the Groundwater Results Application.
- The chemical properties of the PAH compounds found in the BWS wells prevent them from easily dissolving into groundwater and traveling far from where they were released into the environment. They are relatively “sticky” compounds that absorb to clays and organic matter in the soil and aquifer, which greatly reduces their mobility in the subsurface.
Similar to how smoke from a chimney disperses downwind, groundwater contamination disperses and becomes more diluted downstream (downgradient) from its source. Given the 1.7 mile separation distance, EPA expects groundwater contamination from Red Hill would be highly diluted and dispersed before reaching the ʻAiea wells. However, some of the PAHs found in the ʻAiea wells were detected near their solubility limit. This means the PAHs detected in the ʻAiea Wells likely came from a source very close to the wells (or perhaps entered the wells directly through a compromised surface seal) rather than from Red Hill. - As presented at the FTAC in October 2024, the PAHs detected in the ʻAiea wells are likely a pyrogenic source (from burning) and not likely a petrogenic source (from petroleum) and overall, have a different chemical profile than the PAH contamination found at Red Hill. Example: The PAHs detected at the ʻAiea wells are dominated by high molecular-weight PAHs while low-molecular weight PAHs are most prevalent at Red Hill.
- If Red Hill had been a source of the BWS samples, we would have expected to see other petroleum hydrocarbon contamination as well as the PAHs the BWS detected. Example: TPH, methylnaphthalenes, and other chemicals are found at Red Hill and not in the May and June samples from ʻAiea Wells.
- If this were a large plume that traveled nearly 2 miles, we would expect it to persist, and it hasn’t. PAHs were detected on two events and not before or after. EPA is not aware of a site where a PAH plume in groundwater has detached and migrated away from its source, which would be necessary to explain the transient detections.
- Groundwater plumes follow a pattern. During and immediately following a petroleum release, the plume grows rapidly. After the source of release is stopped, the plume stops growing, stabilizes and then begins to contract. Following the November 2021 release from Red Hill, the farthest detections we saw were no more than ¼ to ½ mile from Red Hill. Since that time, the extent and magnitude of contamination have decreased, and current impacts are limited to the tank gallery area. Many of the Navy’s groundwater monitoring wells serve as sentinel wells and provide early warning if contamination plumes are heading toward BWS drinking water wells. EPA is not seeing indications of plume migration in the sentinel wells.
More information can be found in the Hawai'i Department of Health (DOH) FTAC PowerPoint Presentation (pdf).