Siemens Carbon Regeneration Facility
(formerly US Filter Westates)

Risk Assessment

You will need Adobe Reader to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Adobe Reader.

Risk Assessment for the Siemens Water Technology. Corp.

On July 30, 2007, Siemens 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, conducted at the facility in accordance with the regulations for this type of facility. The risk assessment report is below, and the air emissions test report, plus EPA's fact sheets regarding the air emissions test and risk assessment, are on the Air Emmissions page.

This risk assessment was performed according to a USEPA-approved Risk Assessment Workplan (“Work plan”) developed in 2003, updated by agreement with the USEPA to include elements of more recent 2005 USEPA guidance for risk assessments of waste combustion facilities. The USEPA approvals were received prior to the initiation of this study which included evaluations of potential human health and ecological risks associated with both furnace stack air emissions and fugitive air emissions from spent carbon unloading. The assessment also included evaluations of potential risks associated with exposure to the facility’s effluent discharge to the Colorado River Sewage System Joint Venture publicly owned sewage treatment plant and with exposure to airborne chemicals in the workplace at the facility.

The risk assessment used a large amount of site-specific data, including but not limited to: Comprehensive testing of emissions from the furnace stack, with analysis for site specific chemicals of potential concern: Data on spent carbon characteristics, the facility configuration, and facility operations; Local land use and demographic information; Water resources data available from the U.S. Geological Survey and the U.S. Bureau of Reclamation; and Meteorological data from Parker, Arizona.

In the absence of site-specific information, health-protective default values recommended by the USEPA were used. Chemical-specific toxicological data and chemical properties for the compounds selected for evaluation were obtained from the USEPA or from other public health agencies, organizations or databases primarily recommended by the USEPA. In addition, many mathematical models developed by the USEPA and presented in the Agency’s guidance documents were applied to perform the risk assessment calculations. Overall, the models and input data used in the risk assessment are expected to provide conservative (i.e., health protective) estimates of potential risks.

Potential risks from stack emissions into the air were evaluated for over 170 compounds selected for detailed assessment based on a comprehensive performance demonstration test (PDT) approved in advance by the USEPA 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 included compounds that were detected in stack emissions and also over 80 compounds that were not detected but were included in the calculations to ensure that risks would not be underestimated. Stack emission rates for the selected compounds were calculated based on either PDT results, proposed permit limits or, for a few chemicals, long-term average chemical feed rates and a conservative value for the furnace’s destruction and removal efficiency.

Potential risks from fugitive air emissions were evaluated for 21 compounds selected for evaluation based on their concentrations in spent carbon, the number of deliveries and amounts delivered to the facility, chemical toxicity, and volatility. Air dispersion and deposition modeling was conducted using a model developed and approved by the USEPA to allow calculation of chemical concentrations in air and deposition rates onto the earth’s surface 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, and human exposures and risks, were based on current USEPA guidance and solved using the Industrial Risk Assessment Program software.

Top of page

Human Health Risk Assessment

The stack emissions human health risk assessment calculated exposures for several different types of individuals who could hypothetically be exposed to emissions from the plant: adult and child residents, adult and child farmers, adults and children assumed to eat fish caught from the Colorado River or the Main Drain, and a nursing infant. In risk assessment terminology, these groups of individuals are known as “receptors”. Each adult or child receptor was assumed to be exposed through a variety of pathways (e.g., the adult farmer receptor was assumed to be exposed via inhalation, soil ingestion, homegrown produce ingestion, and ingestion of home-raised or locally-raised beef, pork, poultry, and eggs). Each adult receptor was also conservatively assumed to be the mother of a breast-fed infant with the potential for transmission of chemicals from the mother through nursing. The fugitive emissions human health risk assessment evaluated inhalation exposures for adult and child residents, and adult and child farmers.

A variety of risk evaluations were performed in the human health risk assessment, as summarized below:

• Chronic long-term excess lifetime cancer risks from stack emissions were found to be at least five times lower than the USEPA’s combustion risk assessment target level of 1x10-5 (one in 100,000) over a 70-year lifetime when all compounds were included. The excess lifetime cancer risks were reduced to 50 or more times lower than the target risk level when just one compound (that was not detected in the stack gases and has not been received at the facility in spent carbon) was removed from the analysis. Excess lifetime cancer risks due to inhalation of fugitive emissions were at least 200 times below the USEPA target risk level. The excess lifetime cancer risks would remain below the USEPA target risk level even if stack and fugitive emissions were considered together.

• Chronic long-term non-cancer effects from exposure to stack and fugitive emissions were predicted not to occur with a large margin of safety. Calculated exposures were at least 25 times lower and 250 times lower, respectively, than the conservative non-cancer target level used by USEPA for combustion sources, which is a hazard index value of 0.25.

• An analysis of short-term acute inhalation exposures showed that adverse acute effects would not occur with a large margin of safety at assessed residential locations and also at maximum impact points beyond the facility boundary.

• The calculated air and soil concentrations for residential receptors were determined to be below conservatively-derived preliminary remediation goals that have been developed by USEPA Region 9.

Ecological Risk Assessment

An ecological risk assessment was also conducted to evaluate potential effects of stack emissions on selected representative ecological receptors within the facility area. The ecological analysis evaluated potential impacts to wildlife that was considered to be at greatest risk based on habitat use, exposure potential, ecological significance, and population status. The habitat types that were considered consisted of creosote bush scrub, agricultural areas, riparian corridors and backwaters, the Colorado River, and the Main Drain. The species selected for evaluation consisted of aquatic life, plants, the badger, Gambel’s quail, the great horned owl, the burrowing owl, the southwestern willow flycatcher, the double-crested cormorant, the Yuma clapper rail and mule deer. Potential risks were evaluated by comparing calculated concentrations or exposures to toxicity reference values (TRVs) derived to be protective of these receptor groups. The TRVs were obtained from a variety of sources, including the USEPA, the State of Arizona, ecological databases and the published literature.

The calculated environmental concentrations and exposures to animals and birds were not only below the TRVs but also below the conservative ecological target risk level specified by USEPA Region 9 for this project (i.e., a hazard index value of 0.25). These results indicate that adverse ecological effects from exposure to stack emissions are not expected to occur for the evaluated receptors. Concentrations in surface water and sediment were found to be more than 800 times lower than the 0.25 target hazard index level. Concentrations in plants ranged from just below the 0.25 target level to more than 400 times lower than the 0.25 target level. Exposures to selected bird species were found to be at least five times lower than the 0.25 target level. Finally, exposures to the evaluated mammal species were determined to be at least 5,000 times below the 0.25 target level.

Wastewater Discharge from the Facility to the Wastewater Treatment Plant

The risk assessment also evaluated the potential incremental impact of the facility’s wastewater effluent on chemical concentrations discharged from the publicly owned treatment plant into the Main Drain. The analysis also evaluated potential fish tissue concentrations and associated potential human health fish ingestion risks in the Main Drain downstream of the treatment plant’s discharge point. This evaluation focused on 19 compounds selected based on measurements obtained from the facility’s effluent discharge.

This evaluation showed that the incremental contribution of the facility’s effluent on the treatment plant discharge and the Main Drain does not pose unacceptable risks to either aquatic life or human health. The modeled discharge concentrations were below or equivalent to the most stringent applicable state water quality standards and criteria and the treatment plant’s discharge permit limits for all evaluated compounds. Semi-annual toxicity tests performed on the treatment plant’s discharge since 2000 have consistently shown no toxicity to aquatic organisms. Additionally, potential risks due to ingestion of fish caught from the Main Drain associated with the incremental contribution of the SWT facility effluent were all below USEPA target risk levels for both cancer and non-cancer effects.

Worker Evaluation of Fugitive Emissions

The risk assessment included an evaluation of workplace air concentrations associated with spent carbon unloading using methods consistent with those adopted by the U.S. Occupational Safety and Health Administration and the National Institute of Occupational Safety and Health. This analysis compared modeled on-site ambient air concentrations for the 21 selected compounds due to fugitive emissions, to workplace permissible exposure limits. The worker evaluation indicated that ambient air concentrations due to fugitive emissions during spent carbon unloading would not exceed occupational exposure limits within the property boundary. These results were supported by many years of industrial hygiene measurements, which have predominantly shown air concentrations of regulated chemicals to be either below quantitation limits or typically 100 or more times below the occupational standards and criteria.

Conclusion

In conclusion, the risk assessment presented in this document demonstrates that, using conservative assumptions, the potential risks associated with air emissions from the Siemens Water Technologies Corp. carbon reactivation furnace and from spent carbon unloading are below regulatory and other target risk levels for both human health and ecological receptors. Additionally, the incremental contribution of the facility effluent on the wastewater treatment plant discharge and the Main Drain does not pose unacceptable risks to either aquatic life or human health. Finally, fugitive emissions during spent carbon unloading do not exceed occupational exposure limits in ambient air at the facility.