Action Levels
Action levels define the air monitoring thresholds at which action must be taken when levels are exceeded.
The Indiana Department of Environmental Management (IDEM) issued an air registration document which includes emission limits for volatile organic compounds (VOCs) and particulates (PM).
Supplemental Risk Assessment (SRA)
The USEPA conducted an SRA to evaluate the risk of exposure to incremental emissions from the Confined Disposal Facility (CDF). The SRA considered exposure scenarios for cancer and non-cancer health effects through several populations for chronic and acute inhalation exposures as well as various other parameters.
The SRA concluded that the emission limits in the IDEM air registration permit would provide for a health risk that is “relatively low and below USEPA’s established risk level” for nearby residents. Therefore, real-time monitoring is conducted according to the conditions set by the IDEM air registration permit.
Short-Term Action Levels
Short-term action levels were developed to ensure that cumulative daily emissions would not approach the levels described in the IDEM Air Registration Permit and the SRA. The action levels are described in more detail below. These action levels include maximum levels for both particulates (PM) and naphthalene, which was determined to be the most significant hazardous air pollutant (HAP) and VOC that could be emitted from the dredging operations.
The facility operations and dredging contractor are required to ensure that emissions do not exceed the permit limits, and may take the actions described below if emissions approach these levels.
Particulate (PM) Action Levels
The IDEM air registration permit requires property line emissions to be less than 50 µg/m3 above background for 60-minutes for total particulate emissions at the property line (Condition 3b). This limit is below the air registration limit, which was determined in the SRA to be of low health risk and was therefore used as a basis for the action levels.
| Action Level | Amount | Duration | Response |
|---|---|---|---|
| Action Level 1 | 50 µg/m3 above background | 15-minute exceedance | Triggers a heightened awareness of the air monitoring levels |
| Action Level 2 | 50 µg/m3 above background | 30-minute exceedance | Triggers the activation of control measures. The facility operations and dredging contractor then has 30 minutes to respond with appropriate particulate matter emission controls before 1 hour of 50 µg/m3 is reached. No action is required if the exceptions given in 326 IAC 6-4-6 are met (i.e., adverse meteorological conditions 326 IAC 6-4-6 (6)). |
Naphthalene Action Levels
Based on the SRA, naphthalene is as a surrogate compound to represent all VOCs. The toxicity characteristics of naphthalene represent the highest Cancer Slope Factor (CSF) and lowest reference concentration compared to other VOCs typically found at IHC.
There are three action levels for naphthalene, which make up a tiered approach to community protection:
| Action Level | Amount | Duration | Response |
|---|---|---|---|
| Action Level 1 | 150 µg/m3 naphthalene above background | 24-hour average | Triggers a heightened awareness of air monitoring activities and off-loading procedures |
| Action Level 2 | 300 µg/m3 naphthalene above background | 5 consecutive days | Provides the CDF operator an adequate response time prior to reaching the maximum action level |
| Action Level 3 | 5,000 µg/m3 naphthalene above background | 1-hour maximum | Requires the cessation of dredged material off-loading |
These action levels were conservatively determined based on the SRA, which were determined to be both low-risk and protective of human health. For more information on how the action levels were determined, please reference the USEPA Supplemental Risk Assessment or the Air and Water Quality Guidance Document.
During the 9 years of real-time air monitoring, naphthalene levels at the site are virtually all non-detect by the site samplers. Furthermore, naphthalene, even when detected, has never exceeded naphthalene action levels for the CDF site. USACE stopped operating the real-time naphthalene air monitors when the dike expansion began, and it did not restart after dike construction was completed.
PID VOC Monitoring (Historical)
The facility operations and dredging contractor conducted air monitoring for VOCs at a single location in the vicinity of the dock area using a PID for a 30-minute continuous period. This monitoring took place once per day when a barge with dredged material was docked at the site and for 10-days prior to dredging. The PID was set to record 30 minute averages with an alarm at 10 ppm VOCs for heightened awareness and an alarm at 100 ppm VOCs to immediately implement emission controls.
From 2012 through 2020, dock face PID monitoring measurements never exceeded site action levels for VOCs for implementation of emission control measures. Dock face PID monitoring will be discontinued during future dredging.
Responses to Exceeded Action Levels
In general, an initial air quality alarm is intended to trigger awareness by the facility operations and dredging contractor. Upon an initial alarm, the contractor may:
- Determine if the sources are considered upwind or background (meaning the source is from outside the CDF and barges)
- Recalibrate the air monitors or check for other malfunctions
- Take steps in preparing operations for emission controls
The specific types of emission controls the contractor may employ are at their discretion, as site conditions may prove some control measures more effective during operation. These control measures may include, but are not limited to:
- Adjusting the sediment placement rate (to minimize mass transfer to the air)
- Adding additional water cover (to wet particulates or prevent VOC off-gassing)
- Applying foams or tarps
- Applying activated carbon to the slurry line or CDF cells
- Temporarily ceasing all dredging activities
See the Actions Taken page for details on actions taken in response to specific alarms.
