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 communities and rebuild.

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

USACE has taken the following steps to protect human health and ensure that debris and ash removed from Lahaina do not pollute the air and water resources (stormwater, surface waters, and groundwater) around the TDS Site and the PDS:

• Prohibiting large truck dumping when wind speeds are high.

• Using water sprays on high-dust days to keep ash out of the air.

• Covering collected material with clean soil or volcanic rock to reduce windblown dust.

• Setting truck speed limits on dirt roads.

• Diverting stormwater around the TDS Site and the PDS to prevent it from contacting ash and debris. The storm drains throughout the site have inlet protection to prevent harmful substances in stormwater from entering the basin.

• Collecting leachate (liquid, mostly stormwater, that has contacted the active ash/debris storage area) rather than releasing it into the environment. Stormwater that falls on the active TDS area either evaporates, is absorbed by the ash and debris, or flows as leachate to a collection basin (the leachate basin). A thick liner beneath the leachate basin prevents the leachate from leaking into underlying soils. The basin size and location do not allow the leachate to mix with stormwater, so the leachate does not reach surface water. The leachate basin is designed to hold over 1 million gallons, which is much more than the amount of leachate expected to be generated. Leachate collected in the basin does not flow outside the TDS Site.

• Constructing the TDS Site in a location that is downgradient (below) public drinking water sources to mitigate any potential for contamination of drinking water sources from the TDS Site.

TDS Site Air Monitoring

USACE contractors used air monitors to measure airborne particles (both PM_2.5 and PM₁₀) near debris removal sites and continue to use them around the TDS Site (Figure 3). The number and locations of air monitors at the TDS Site may vary based on weather conditions and operations. USACE’s 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 vary, 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 are being taken through the completion of transfer and closure operations. Figures 4 and 5 show that all measurements for both PM_2.5 and PM₁₀ have been 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 recent site monitoring reports are available here.

USACE is also providing air monitoring of the TDS to PDS transfer. Reports and data on these results are available here.

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. Results and interpretation of associated sampling data are further discussed here.

TDS Site Leachate Sampling

Once enough leachate has collected in the leachate basin, USACE takes samples and measures the amounts of potentially harmful substances in the leachate. Results of parameters of the greatest concern from sampling are shown below (Table 1), with full results available for download here.

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

The leachate basin is lined and undamaged and, as such, there has been no evidence of leachate leaking to underlying soils or groundwater. Given the lining and facility life, leachate is not expected to enter the groundwater due to the facility design and construction features. Still, USACE installed wells to monitor the groundwater upgradient (uphill) and downgradient (downhill) from the TDS Site to confirm that leachate does not enter the groundwater.

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

¹As of 8/29/2025, the most recent round of leachate sampling occurred on 2/3/2025
< = 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 samples the leachate basin periodically and samples the basin monthly if a rainfall event of more than 1 inch takes 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; data can be found here. These data show that the levels of fire-related substances present in surface water do not pose a risk to human health.

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 has a depth of 328.92 feet, and Monitoring Well 02 has a depth of 158.53 feet. USACE is sampling and analyzing the groundwater for similar potential contaminants of concern as leachate. USACE is comparing the downhill well sample results to the uphill well sample results to identify if fire-related substances are entering the groundwater from the TDS Site. USACE collected groundwater samples in July, October, and December of 2024, as well as in February, May, and August of 2025. These data are presented in Table 2. The groundwater monitoring results indicate no fire-related substances are reaching groundwater.