Environmental Monitoring

Maui Wildfire Data: West Maui Temporary Debris Storage (TDS) Site

Debris removal in Lahaina was a critical step in the larger wildfire recovery efforts. Debris removal involved clearing and disposing of materials and waste burned in the fire, some of which may have been hazardous to human health. It involved a controlled process to ensure the safe collection, removal, transportation, and storage of debris so that people could safely re-enter their neighborhoods and rebuild.

Sampling data collected to date show that the West Maui Temporary Debris Storage Site did not release harmful substances into the environment at levels of health concern.

• After Lahaina cleanup efforts were completed, the TDS Site was temporarily closed and secured.

• Ash and debris were loaded out and secured with polyethylene plastic liners with additional tarps during transport by truck to the PDS.

• Trucks leaving the loadout area passed across mats designed to remove debris and prevent tracking out of material along the access road.

• Earthen cover was replaced daily to control dust at the TDS Site and the PDS.

• Water trucks were used to control dust during excavation, loading, and loadout.

• The County of Maui worked with DOH and USACE to monitor both the PDS and the TDS Site as transfer to the PDS took place, including dust monitoring and perimeter air monitoring. Current air monitoring reports are available for download. 

• Leachate monitoring, stormwater diversion, and groundwater monitoring took place throughout TDS Site closure operations. 

• After the debris transfer from the TDS Site to the PDS was completed, the protective liner at the TDS Site was removed and soil sampling was conducted to ensure no impact on the land or public health. Post-use data were well below action levels and showed no impact to the site. 
• The groundwater monitoring wells were properly decommissioned and 
  removed on December 18 and 19, 2025. 
• TDS Site areas were graded and restored to as close to original conditions as possible as of December 19, 2025, and best management practices and run-on/runoff management will be maintained as necessary. 

TDS Site Air Monitoring

USACE contractors used air monitors to measure airborne particles (both PM_2.5 and PM₁₀) near debris removal sites. The number and locations of air monitors at the TDS Site varied based on weather conditions and operations. USACE’s air monitoring data for 2024 and 2025 are shown in Figures 4 and 5. The figures show particulate matter concentrations averaged between the two monitoring sites around the TDS Site. Particulate matter concentrations at individual monitoring sites varied, with some higher and some lower than the averages shown. Air monitoring was paused from April 30, 2025, to June 17, 2025, when the TDS Site was temporarily closed and no site operations were taking place. Monitoring resumed when transfer to the PDS began, and daily samples were taken through the completion of transfer and closure operations in November 2025. Air monitoring was paused again from November 21–30, 2025, and then resumed until the completion of the project. Figures 4 and 5 show that all measurements for both PM_2.5 and PM₁₀ were below their respective action levels set for operating the TDS Site (35 μg/m³ for PM_2.5 and 150 μg/m³ for PM₁₀).

USACE’s site monitoring reports are available for download.

USACE also provided air monitoring of the TDS to PDS transfer.

DOH provides real-time air monitoring at locations throughout the Olowalu community. These data are posted in near-real time to https://fire.airnow.gov/. All DOH measurements of airborne fine particles (PM_2.5) in the Olowalu community to date indicate that airborne particles have not reached levels of health concern. The Air page includes further discussion of results and associated sampling data.

TDS Site Leachate Sampling

USACE sampled and measured the amounts of potentially harmful substances in the leachate after storm events of 1 inch or greater. Results of parameters of the greatest concern from sampling are shown below (Table 1), with full results available for download. The final leachate sample was taken on October 9, 2025, and the leachate basin was removed in November, along with the remaining leachate and sediment, as part of TDS closure operations.

The presence of potentially harmful substances in the leachate basin was not a public health concern because people did not enter the basin or drink the water, and the site was not above a groundwater source of drinking water and was downgradient (downhill) of public water supplies.

The leachate basin was lined and undamaged and, as such, there has been no evidence of leachate leaking to underlying soils or groundwater. Still, USACE installed wells to monitor the groundwater upgradient (uphill) and downgradient (downhill) from the TDS Site to confirm that leachate did not enter the groundwater.

Note that the “baseline stormwater” sample data shown in Table 1 was from stormwater that had collected in the leachate basin, not leachate from the TDS Site, as discussed below.

¹As of 12/15/2025, the most recent round of leachate sampling occurred on 10/9/2025
<: less than
ND: non-detect
NS: not sampled

TDS Site Stormwater Sampling

In early January 2024, over 3 inches of rain fell in less than 24 hours at the empty TDS Site. The site was under construction and debris had not yet been stored at the site. USACE sampled the rainwater from the storm that had collected in the leachate basin on January 11, 2024, the results of which are shown in the table as “(baseline stormwater).”

USACE sampled the leachate basin periodically and sampled the basin monthly if a rainfall event of more than 1 inch took place during the month. The latest monitoring results are presented in Table 1.

TDS Site Surface Water Sampling

In addition to USACE site-specific monitoring, DOH is collecting coastal water samples near the TDS Site. These data show that the levels of fire-related substances present in surface water do not pose a risk to human health. Based on the results of recent sampling, DOH may conduct additional water quality sampling after closure of the TDS Site.

TDS Site Groundwater Sampling

USACE installed two temporary groundwater monitoring wells uphill (Monitoring Well 01) and downhill (Monitoring Well 02) of the TDS Site. Well construction began during June 2024 and was completed on July 10, 2024. Monitoring Well 01 had a depth of 328.92 feet, and Monitoring Well 02 had a depth of 158.53 feet. USACE sampled and analyzed the groundwater for similar potential contaminants of concern as leachate. USACE also compared the downhill well sample results to the uphill well sample results to identify if fire-related substances were entering the groundwater from the TDS Site. USACE collected groundwater samples in July, October, and December of 2024, as well as in February, May, August, and November of 2025. These data are presented in Table 2. In November 2025, USACE collected the final groundwater sample; these data are shown in Table 2. The groundwater monitoring results indicate no fire-related substances are reaching groundwater.