Cahaba River Wastewater Treatment Plant - Executive Summary |
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Policy Statement It is the Jefferson County Environmental Services Department's (JCESD) policy to operate safe wastewater treatment plants (WWTPs), reducing to the greatest extent possible any hazards associated with the necessary treatment processes and reducing any subsequent risk to the surrounding community, personnel, and environment. The policy includes working with the surrounding community and local emergency response agencies to promote a spirit of cooperation and teamwork and to orchestrate an effective contingency plan in the unlikely event of a process incident occurring at the Cahaba River WWTP. It is the JCESD's policy to adhere to all applicable federal, state, and local laws applicable to Cahaba River WWTP. Although not required by regulation, the JCESD has installed a chlorine/sulfur dioxide scrubber to reduce risk to the surrounding community, personnel, and environment at the Cahaba River WWTP in the event of a release. Description of Facility and the Regulated S ubstance Handled The Cahaba River WWTP is a municipal wastewater treatment plant. Chlorine and sulfur dioxide are used for the chlorination and dechlorination of wastewater prior to returning the treated wastewater to the environment. Chlorine is used primarily as a disinfectant. Other possible uses of chlorine are for odor control and to assist in settling of biosolids in the clarification process. The maximum quantity of chlorine stored at the facility is eight 1-ton containers, equivalent to 16,000 pounds. The chlorination system consists of vacuum regulators, automatic switchover system, chlorine gas dispensers, chlorine leak detectors, alarms, a chlorine/sulfur dioxide scrubber, associated piping, valves, and other miscellaneous equipment. Sulfur dioxide is used for dechlorinating the effluent before it is discharged into the Cahaba River. The maximum quantity of sulfur dioxide stored at the facility is eight 1-ton containers, equivalent to 16,000 pounds. The dechlorination system consists of vacuum regulators, automatic switchover system, sulfur dioxide gas dispensers, sulfur dioxide leak detectors, alarms, a chlorine/sulfur dioxide scrubber, associated piping, valves, and other miscellaneous equipment. Worst-case and Alternative Release Scenarios The EPA defined the worst-case scenario as the failure of one liquid sulfur dioxide container resulting in a release of 2,000 pounds of sulfur dioxide in 10 minutes. The sulfur dioxide containers are stored in an enclosed building. Therefore, the release rate is reduced substantially because of passive mitigation provided by the building enclosure, which restricts the rate at which sulfur dioxide can disperse to the outside atmosphere. The estimated distance to the endpoint of the worst-case scenario is 1.68 miles, beyond which there will be enough dispersion to reduce the concentration below the toxic endpoint. The total population affected by this hypothetical worst-case release is estimated to be 14,8 00 people, based on 1990 Census Data. Realistically, the JCESD does not anticipate that the worst-case scenario could actually happen. A chlorine/sulfur dioxide scrubber has been installed to control any release of either chlorine or sulfur dioxide from the process. EPA does not allow the beneficial effects of the scrubber to be considered in the evaluation of a facility's WRS. JCESD has developed alternative release scenarios (ARSs) for both chlorine and sulfur dioxide because these scenarios are more realistic "worst-case" scenarios. The chlorine ARS is the release of chlorine gas from a <-inch-diameter pipe connecting the chlorine container to the feed manifold. This scenario was selected because it is the most likely failure scenario, based on the experience of the plant operators who participated in the hazard review. It is estimated that the release will require approximately 22 minutes before a trained mechanic can repair the leak. Taking into account active mitigation b y the scrubber, the chlorine release rate of 0.032 kg/s is reduced to 0.0003 kg/s, based on 99 percent scrubber efficiency. The estimated distance to the endpoint for the alternative release scenario is 0.057 mile. The total population within the distance to the endpoint for the alternative release is estimated to be 20 people, based on 1990 Census Data. The sulfur dioxide ARS is the release of sulfur dioxide gas from a <-inch-diameter pipe connecting the sulfur dioxide container to the feed manifold. This scenario was selected because it is the most likely failure scenario, based on the experience of the plant operators who participated in the hazard review. It is estimated that the release will require approximately 22 minutes before a trained mechanic can repair the leak. Taking into account active mitigation by the scrubber, the sulfur dioxide release rate of 0.032 kg/s is reduced to 0.0003 kg/s, based on 99 percent scrubber efficiency. The estimated distance to the endpoint f or the alternative release scenario is 0.058 mile. The total population within the distance to the endpoint for the alternative release is estimated to be 20 people, based on 1990 Census Data. General Accidental Release Prevention Program and Chemical-specific Prevention Steps The Cahaba River WWTP has complied with the requirements of the Risk Management Program (RMP) Rule, 40 CFR 68. The facility has conducted a comprehensive review of all systems, as well as administrative, technical, and operating and maintenance procedures, in addition to the other required program elements of the RMP Rule. A detailed hazard review was conducted at this facility using a "What-If" analysis. Five-year Accident History The Cahaba River WWTP has never had a release of chlorine or sulfur dioxide resulting in injuries, deaths, property or environmental damage, evacuations, or shelterings in place. The effectiveness of the facility's design, operating procedures, and training has resulted in an exc ellent safety record. Emergency Response Program The JCESD has an Emergency Response Plan for the Cahaba River WWTP that coordinates response efforts with the Hoover Fire Department's HAZMAT team, the police department, and the hospital. Response activities also have been coordinated with the Jefferson County Local Emergency Planning Committee (LEPC). Planned Changes to Improve Safety It was observed during the hazard review that the Cahaba River WWTP has the necessary equipment and the operating and training procedures required for the safe operation of the chlorination and dechlorination systems. Therefore, no recommendations were made. |