Environmental Monitoring

Maui Wildfire Data: Coastal Sediment

Ash from the Maui wildfires has entered sediment (a solid material that contains sand, minerals, and other substances) in ditches, streambeds, and along the shore. The ash may have settled from the air or may have been carried by stormwater runoff. Solid ash particles in water eventually settle into sediment.

DOH and partners continue to test to understand and determine the levels of fire-related substances in sediment, remediation needs, and possible health and safety concerns.

Monitoring to date confirms that the coastal waters around Lahaina are safe for recreation and that concentrations of potentially harmful fire-related substances are well below levels of human health concern.

Coastal Sediment Sampling

DOH is reviewing data from the following sampling efforts to evaluate sediment quality:

• DOH began collecting quarterly nearshore sediment samples from nine sites throughout Lahaina in May 2024. Sampling continued in 2025 and 2026 at six sites, targeting the key areas where changes were observed.
• The Department of Land and Natural Resources (DLNR) collected 20 sediment samples from 17 sites at the Lahaina Small Boat Harbor on November 16, 2023. The fires burned vessels and boats in the Harbor, which may have released harmful substances and debris into nearby water and sediment. The primary purpose of the sampling was to determine whether it would be safe to dispose of sediment in upland areas. Samples were collected from sediment depths ranging from approximately 0.5 to 4 feet below the sea floor.
• U.S. Geological Survey (USGS) sampled numerous locations for a wide range of substances, including potentially fire-related substances. While the data provide context, they are preliminary and not suitable for decision-making. The USGS samples were not collected using DOH protocols for assessment of health risk and cannot be used to assess potential health risks. Nonetheless, the data do not suggest potentially significant health concerns.

Figure 2. Interactive time series of nearshore sediment sample results collected by DOH from May 2024 through February 2026. Hover over the points to see results in a pop-up.

DNLR collected sediment samples from 17 sites at the Harbor on November 16, 2023 (Figure 3).

The samples were analyzed for more than 85 parameters, including metals, total petroleum hydrocarbons-diesel range organics (TPH-DRO), dioxins, and others. Table 1 presents a subset of the results, with a focus on fire-related substances of potential concern (substances known to stick to wildfire dust and ash) at sampling locations.

As shown in Table 1, reported levels are below DOH’s commercial/industrial EALs for direct soil exposure. The results of the initial screening indicate that sediments could be dredged and may be suitable for upland disposal and reuse at commercial or industrial sites as fill material or daily landfill cover. However, additional sampling and analysis are needed to evaluate final suitability decisions for sediment reuse.

Sediment data provided by DLNR.
DOH EAL: Hawaii DOH Environmental Action Level for screening. An entry of “—” means the analyte does not have an EAL.
TPH-DRO: Total petroleum hydrocarbons – diesel range organics
ND: Non-detect
TEQ Dioxins: “Toxic equivalent concentration” that allows the reporting of multiple dioxin/dioxin-like chemicals as a single value based on their relative toxicities.
¹Screening values represent soil EALs for commercial/industrial land use obtained from DOH’s TGM EAL Surfer (Tier 1 EALs) search function (found here: Environmental Hazard Evaluation and Environmental Action Levels – HEER Office (hawaii.gov) (opens in a new tab)) at the time of data release (December 2023).

Grab sample sediment data provided by USGS; sampling locations are listed as presented by USGS as “marine sediment.”
An entry of “—” means the analyte does not have an EAL.
Data are provisional and not suitable for decision-making.
ND: Non-detect
TEQ Dioxins: “Toxic equivalent concentration” that allows the reporting of multiple dioxin/dioxin-like chemicals as a single value based on their relative toxicities.

Grab sample sediment data provided by USGS; sampling locations are listed as presented by USGS as “marine beach.”
An entry of “—” means the analyte does not have an EAL.
Data are provisional and not suitable for decision-making.
ND: Non-detect
TEQ Dioxins: “Toxic equivalent concentration” that allows the reporting of multiple dioxin/dioxin-like chemicals as a single value based on their relative toxicities.

Grab sample sediment data provided by USGS; sampling locations are listed as presented by USGS as “marine beach.”
An entry of “—” means the analyte does not have an EAL.
Data are provisional and not suitable for decision-making.
ND: Non-detect
TEQ Dioxins: “Toxic equivalent concentration” that allows the reporting of multiple dioxin/dioxin-like chemicals as a single value based on their relative toxicities.