West River Wastewater Treatment Plant - Executive Summary
Policy Statement |
It is the policy of The Water Works and Sewer Board of the City of Gadsden (GWWSB) to operate safe water and wastewater treatment plants, reducing to the greatest extent practicable 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 West River Wastewater Treatment Plant (WWTP). It is the GWWSB's policy to adhere to all applicable federal, state, and local laws applicable to the West River WWTP.
Description of Facility and the Regulated Substance Handled
The West River WWTP is a publicly owned and operated wastewater treatment facility. Chlorine is used primarily for the destruction of pathogenic microorganisms in t
he effluent and to provide chlorine for prechlorination and trim chlorination. Other possible uses of chlorine are for odor control and to assist in settling biosolids in the clarification process. The maximum quantity of chlorine stored at the facility is 8,000 pounds (four 1-ton containers). The chlorination system consists of vacuum regulators, chlorinator, injectors, chlorine leak detector, alarm, associated piping, valves, and other miscellaneous equipment.
Chlorine Worst-case and Alternative Release Scenarios
The EPA-defined worst-case scenario is the failure of one liquid chlorine container resulting in a release of 2,000 pounds of chlorine in 10 minutes. The chlorine containers are stored in the Chlorination Building, which has two doors facing each other that normally are kept open. Therefore, passive mitigation is not considered. The release rate of 1.51 kg/s is modeled using DEGADIS 2.1. Under the worst-case weather conditions prescribed by the RMP Rule, the distan
ce to a toxic endpoint of 3 ppm is 1.86 miles, beyond which there will be enough dispersion that the hazard to the public will no longer exist. The total population affected by this hypothetical worst-case release is estimated to be 13,000 people, based on 1990 Census Data. Realistically, the GWWSB does not anticipate that the worst-case scenario could actually happen. In the event of a total rupture of a 1-ton container of chlorine, most of the chlorine would remain in liquid form until the fire department's Hazardous Material (HAZMAT) team could neutralize the release.
The GWWSB has developed an ARS for chlorine at the West River WWTP that is a more realistic "worst-case" scenario. The 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 GWWSB personnel who participated in the hazard review. It is estimated t
hat the release would require approximately 15 minutes before a trained mechanic could repair the leak. Taking passive mitigation into account, the estimated distance to the endpoint for the ARS is 0.37 mile. The total population within the distance to the endpoint for the alternative release is estimated to be 520 people, based on 1990 Census Data.
General Accidental Release Prevention Program and Chemical-specific Prevention Steps
The GWWSB has complied with the requirements of the RMP Rule, 40 CFR Part 68, for the West River WWTP. A comprehensive review of all systems, as well as administrative, technical, and operating and maintenance procedures has been conducted, in addition to the other required program elements of the RMP Rule. A detailed hazard review was conducted for the West River WWTP using a "What-If" analysis.
Five-year Accident History
The West River WWTP has never had a release of chlorine resulting in injuries, deaths, property or environmental damage, evacuatio
ns, or shelterings in place. The effectiveness of the facility's design, operating procedures, and training has resulted in an excellent safety record.
Emergency Response Program
The GWWSB has implemented an Emergency Response Program for the West River WWTP, which coordinates response efforts with the Gadsden/Etowah County Emergency Management Agency (EMA), the Gadsden fire department's HAZMAT team, the police department, and the hospital.
Planned Changes to Improve Safety
It was observed during the hazard review that the West River WWTP has the necessary equipment and the operating and training procedures required for the safe operation of the chlorination system. However, the following recommendations for improving the safety of the chlorination process were made:
1. Change the chlorine detector set point to 3 ppm, and inspect detectors quarterly
2. Install windsock to indicate wind direction
3. Provide copy of emergency response plan to the fire department