Environmental Monitoring

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

Debris removal in Lahaina is a critical step in the larger wildfire recovery efforts. Debris removal means clearing and disposing of materials and waste burned in the fire, some of which can be hazardous to human health. It involves a controlled process to ensure the safe collection, removal, transportation, and storage of debris so that people can safely re-enter their communities and begin rebuilding.

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.

Debris, ash, and soil from U.S. Army Corps of Engineers (USACE) debris removal operations are transported to the West Maui Temporary Debris Storage (TDS) Site. There, the debris is carefully managed to avoid creating new environmental problems. USACE, DOH, and partners collect environmental samples to ensure that the debris is properly managed. The County of Maui’s Bill 120 requires TDS Site operators to conduct monitoring and publish the sampling results in a report to the public every 90 days. The monitoring checks whether harmful substances at the TDS Site are entering the air, the groundwater beneath the site, or the water that runs through the TDS Site.

USACE takes 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:

Air

• 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.

Stormwater, Surface Water, Leachate, and Groundwater

• Diverting stormwater around the TDS Site 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 does 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.

Moving to the Permanent Disposal Site (PDS)

The West Maui TDS Site is intended only as a temporary site for ash and debris disposal until a Permanent Disposal Site (PDS) can be constructed. On February 28, 2024, Mayor Richard Bissen announced that the PDS will be at the Central Maui Landfill. Once the PDS is constructed and operational, ash and debris will be transferred from the TDS Site to the PDS. This process will begin in 2025. The County of Maui and USACE are currently developing a plan with processes and procedures for the safe loading, transportation, and disposal of ash and debris at the PDS as well as closure of the TDS Site:

• After Lahaina cleanup efforts are complete, the TDS Site will be temporarily closed and secured.
• The County of Maui will work with DOH and USACE to monitor the TDS Site.
• When the PDS is constructed and ready (expected mid-2025), debris will be transferred to it.
• The protective liner will be removed and soil sampling at the TDS Site will be conducted to ensure no impact on the land or public health.
• The groundwater monitoring wells will be properly removed and sealed.
• TDS Site areas will be graded as close to original conditions as possible.
• Plans and progress, including transfer route, will be communicated to the public.

The transfer of debris from the TDS Site to the PDS and the TDS Site closure is expected to take about one year. For more information on this process, the public can contact the USACE hotline (877-214-9117) or the County of Maui. Additional information about the TDS–PDS Transfer and Closure Plan is on the mauirecovers.org site here.

TDS Site Air Monitoring

USACE contractors use air monitors to measure airborne particles (both PM_2.5 and PM₁₀) near debris removal sites and the TDS Site (Figure 1). USACE’s data (Figure 2) show the measurements, all of which have been below the action levels set for operating the TDS Site. USACE’s recent site monitoring reports are available here.

DOH also provides real-time air monitoring at locations throughout the Olowalu community. These data are posted in near-real time to https://fire.airnow.gov/. The number and locations of air monitors at the TDS Site may vary based on weather conditions and operations. All DOH measurements of airborne fine particles (PM_2.5) around the TDS Site 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 recent 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 has recently installed wells to monitor the groundwater upgradient (uphill) and downgradient (downhill) from the TDS Site to confirm that potentially harmful substances in the leachate basin do 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 12/13/2024, the most recent round of leachate sampling occurred on 5/20/2024
< = 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 will sample 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 the first set of groundwater samples on July 7, 2024, and collected a second round of samples on October 8. These data are presented in Table 2. The groundwater monitoring results indicate no fire-related substances are reaching groundwater.