Water 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 Water Treatment Plant (WTP). It is the GWWSB's policy to adhere to all applicable federal, state, and local laws applicable to the WTP.
Description of Facility and the Regulated Substance Handled
The WTP is a publicly owned and operated water treatment facility. Chlorine is used primarily to prevent the spread of disease from the finished water by destroying any pathogenic microorganis
ms that might be left after filtration. Disinfecting the finished water protects consumers from bacteria such as Cryptosporidium and giardia that cause severe illness and gastrointestinal disorders. Another possible use of chlorine is for odor control. The WTP has two chlorination facilities, one for finished water chlorination and the other for raw water chlorination. The maximum quantity of chlorine stored at the finished water chlorination facility 12,000 pounds (six 1-ton containers). The maximum quantity of chlorine stored at the raw water chlorination facility 16,000 pounds (eight 1-ton containers). The chlorination system at the finished water and raw water facilities consists of vacuum regulators, chlorinators, injectors, chlorine leak detectors, alarms, 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 rele
ase of 2,000 pounds of chlorine in 10 minutes. The raw water chlorination facility has all chlorine containers located inside the enclosed building. The finished water chlorination facility has two of the containers stored outside. 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 distance to a toxic endpoint of 3 ppm is 1.82 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 12,470 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 rele
The GWWSB has developed an ARS for chlorine at the WTP 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 that the release would require approximately 15 minutes before a trained mechanic can repair the leak. Taking into account passive mitigation, the estimated distance to the endpoint for the alternative release scenario 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 WTP. A comprehensive review of all sy
stems, 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 WTP using a "What-If" analysis.
Five-year Accident History
The WTP had a release of less than 2 pounds of chlorine during a container changeover on March 11, 1997, at 7:30 a.m. The release lasted approximately 3 minutes. A valve on the cylinder did not fully close, and when the yoke was disconnected, chlorine in the piping escaped and injured two employees. The fire department was notified and responded within minutes. The injuries sustained by the two employees were from inhalation of the chlorine gas; they were provided with first aid at the hospital. No hospital stay was required. The release did not result in any deaths, property or environmental damage, evacuations, or shelterings in place. This incident could have been avoided by following the standard o
perating procedure of leak checking before disconnecting the yoke. The employees were retrained in the operating procedures and the faulty valve was replaced.
Emergency Response Program
The GWWSB has implemented an Emergency Response Program for the WTP, 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 WTP 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. Inspect chlorine leak detectors quarterly
2. Install windsock to indicate wind direction
3. Provide copy of emergency response plan to the fire department