Desotec US LLC (Formerly Evoqua Water Technologies LLC): Air Emissions and Risk Assessment

• Human Health Impacts
• Stack Emissions
• Fugitive Emissions
• Summary Risk Assessment
• Technical Risk Assessment

Human Health Impacts From Air Emissions

At EPA’s request, and as part of the permit process, Evoqua completed a Human Health and Ecological Risk Assessment in July 2007. The purpose of the risk assessment was to estimate the facility’s current and possible future impacts on the health of local residents and the surrounding environment. Based on the risk assessment study, EPA concluded that human health impacts from long-term exposure to stack emissions, fugitive emissions, as well as the combination of the two, were below EPA’s acceptable thresholds.

Stack Emissions

To measure stack emissions, Evoqua conducted a test of the regeneration furnace (trial burn) under specific operating conditions (e.g., temperature of the furnace, amount of carbon being processed by facility, contaminants present in the spent carbon). The concentrations of contaminants coming out of the stack were measured during the trial burn. Computers helped model how emitted substances would disperse (spread) throughout the air and soil in a 154-square mile area surrounding the facility.

Fugitive Emissions

Fugitive emissions are generated during unloading of the spent carbon that comes into the Desotec facility (see Figure 2 in EPA Fact Sheet: Proposed Permit for the Evoqua Water Technologies LLC Facility Near Parker, Arizona (pdf) (732.11 KB, September 2016) ). The risk assessment determined levels of fugitive air emissions from information on amounts of spent carbon that Desotec handles, as well as the concentrations of contaminants in that spent carbon.

Risk Assessment

On July 30, 2007, Evoqua submitted its Human Health and Ecological Risk Assessment Report to EPA. The risk assessment uses the results from the final March 2006 air emissions test (also known as the Performance Demonstration Test or trial burn), which was conducted at the facility in accordance with EPA regulations.

The risk assessment demonstrates that, even using conservative assumptions:

• The potential risks associated with air emissions from both the facility’s carbon regeneration furnace and from spent carbon unloading are below regulatory and other target risk levels for both human health and ecological receptors;
• The incremental contribution of wastewater effluent from the facility’s wastewater treatment plant and the Main Drain discharge canal does not pose unacceptable risks to either aquatic life or human health; and,
• Both concentrations of fugitive emissions from carbon unloading at the facility and measured worker breathing zone concentrations are below occupational exposure limits.

In conclusion, this risk assessment demonstrates that, even with conservative assumptions, the potential risks associated with facility operations are below regulatory and target levels.

Risk Assessment Technical Information

During the development of the risk assessment, potential risks from stack air emissions were evaluated for over 170 compounds. These were selected for detailed assessment based on a comprehensive performance demonstration test (PDT or trial burn). This test was approved in advance by EPA and conducted at the facility by an independent testing firm. The PDT involved several days of stack gas sampling and sophisticated chemical analysis.

The list of chemicals selected for evaluation in the risk assessment included both compounds that were detected in stack emissions, as well as over 80 other compounds not detected, but included in the calculations just to be safe. Stack emission rates for all the selected compounds were calculated based on either PDT results, proposed permit limits, or, for a few chemicals, long-term average chemical feed rates. A conservative value was also used for the furnace's destruction and removal efficiency in the calculations.

Potential risks from fugitive air emissions (rather than stack emissions) were evaluated in the risk assessment for 21 compounds. These were selected for evaluation based on the contaminant concentrations in the spent carbon, the number and amount of deliveries to the facility, the chemical toxicity, and the volatility of the compounds. Air dispersion and deposition modeling was conducted using a model developed and approved by EPA. This model calculated chemical concentrations in the air and ground deposition rates within a 154-square mile study area surrounding the facility. The mathematical equations used to calculate the fate and transport of each chemical in the environment, environmental concentrations for each chemical, human exposures and risks were based on current EPA guidance and solved using the Industrial Risk Assessment Program software.