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 daily fill or Soiltac® (a biodegradable soil stabilization and dust control product) to reduce windblown dust.
• Setting truck speed limits on dirt roads on high wind days.

Stormwater, Surface Water, Leachate, and Groundwater

• Diverting stormwater around the TDS Site to prevent it from contacting ash and debris. The diverted stormwater is collected in a “percolation basin.” 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 TDS Site) 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, referred to as the “leachate basin.” A thick liner beneath the leachate basin prevents the leachate from leaking into groundwater. The basin size and location does not allow the leachate to mix with stormwater, and thus, does not reach surface water. The leachate basin is designed to hold 1.375 million gallons, which is much more than the amount of leachate expected to be generated. Leachate collected in the basin evaporates; it does not flow outside the TDS Site.
• Planning and installing the TDS Site in a location that is downgradient (below) public drinking water sources, and thus, mitigating the contamination of drinking water sources from the TDS Site.

TDS Site Air Monitoring

Two types of air sampling take place at and near the TDS Site. First, DOH measures airborne fine particles (PM_2.5) at five locations around the TDS Site. All measurements to date indicate that airborne particles near the TDS Site have not reached levels of health concern. These sampling data are further discussed here.

Second, USACE contractors use air monitors to measure airborne particles (both PM_2.5 and PM₁₀) near debris removal sites and at the TDS Site. 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.

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 (1) people do not enter the basin or drink the water and (2) the site is not above a groundwater source of drinking water and is downgradient (downhill) of public water supplies.

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.

< = less than

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, DOH, and partners will share other stormwater sampling data here once they are available.

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.

TDS Site Groundwater Sampling

USACE installed temporary groundwater monitoring wells uphill and downhill of the TDS Site during June 2024. Since the leachate basin is lined and undamaged, there has been no evidence of leachate leaking to groundwater and USACE will be conducting monitoring to confirm that no leachate is reaching groundwater. Once groundwater data are available, they will be shared on this page.