Wildcat Hill Wastewater Treatment Plant - Executive Summary
Executive Summary |
The Wildcat Hill Wastewater Treatment Plant (WWTP) is one of the facilities owned and operated by the City of Flagstaff. Wildcat Hill WWTP has prepared a Risk Management Plan (RMP) in accordance with the EPA and OSHA regulatory requirements. A brief overview of the RMP and the associated policies at this facility is described below.
Prevention and Response Policies
The City takes an active role in preventing accidental releases by ensuring that its employees are properly trained in the safe operation of covered processes and the safe handling of treatment chemicals. The City has also established and maintains procedures for emergency notification and response. These are reviewed with employees on a periodic basis and revised to accommodate changes in staffing when they occur. To increase employee safety and awareness, the City:
* maintains up-to-date safety information and operating procedures,
* performs regular preventative maintenance,
* provides periodic refresher training on safe handling of chemicals, and
* conducts periodic safety drills.
Facility Description and Regulated Substances
Wildcat Hill WWTP disinfects wastewater from residential, commercial, and industrial sources through a series of physical, chemical, and biological treatment operations that include:
* preliminary treatment,
* primary sedimentation,
* activated sludge for carbonaceous BOD removal,
* nitrification and denitrification,
* secondary sedimentation,
* chlorination, and dechlorination.
The regulated substances handled at Wildcat Hill WWTP are chlorine and sulfur dioxide. Each chemical is stored in 1-ton (2,000 lbs) containers, with a maximum of 15 chlorine containers and 8 sulfur dioxide containers stored on-site.
Worst-case and alternative release scenarios have been determined after careful revi
ew of the regulation and consideration of the storage vessel configuration at the facility. The EPA's software program RMP*Comp was used to model both release scenarios and to determine the radius of impact.
In the worst-case release scenarios, the regulation clearly states the release quantity shall be the contents of the single largest vessel of the covered process chemical, at ground level and under very stable atmospheric conditions. These conditions are most likely to result in a cloud of the released chemical remaining intact as it slowly moves along the ground. Planning for an accidental release under these unlikely conditions provides the City with additional safety margin in protecting the public.
As required by regulation, the worst-case scenario for chlorine assumed the complete release of chlorine from a single container (2,000 lbs). Similarly, the worst-case scenario for sulfur dioxide assumed the complete release of chemical from a single container (2,000
lbs). In addition, no mitigation effects, such as a release inside a storage building, were considered for either chemical.
For the alternative release scenario for chlorine, the assumptions were that (a) a failure occurred in the ton container valve, and (b) 1,200 lbs of chlorine were released over a 60-minute period before the leak could be repaired. The passive mitigation effect of the storage building reduces the amount of chlorine released to the atmosphere by 55% (from 1,200 lbs to 660 lbs).
For the alternative release scenario for sulfur dioxide, the assumptions were that (a) a failure occurred in the ton container safety device (fusible plug), and (b) 400 lbs of sulfur dioxide were released over a 60-minute period before the leak could be repaired. No mitigation effects, such as a release inside the sulfur dioxide storage building, were considered.
Prevention Steps for Chlorine and Sulfur Dioxide
The prevention program fulfills the requirements of the O
SHA Process Safety Management (PSM) rule and the EPA RMP rule, and includes:
* formal and on-the-job training,
* written operating procedures, and
* a process equipment preventive maintenance program.
There has been no release of either covered chemical in the past five years.
Emergency Response Program
Wildcat Hill WWTP has established and maintains an emergency action plan that is coordinated with local response agencies. The goals of the program are to protect on-site employees from the hazardous effects of a release and to minimize the effects of releases on the general public. The program is routinely reviewed and updated to reflect personnel and regulatory changes.
Planned Changes for Improved Safety
Ideas for changes to improve safety are actively sought from employees. Employee meetings that focus on safety issues are held regularly at the facility. Employees are encouraged and trained to recognize hazards and present id
eas to eliminate them or to minimize the potential consequences of those hazards.
During the development of this RMP document, process hazard analyses of the chlorine and sulfur dioxide systems were conducted with key employees to fulfill the prevention program requirements. During these sessions, recommendations were made for the purpose of improving safety and preventing accidental chemical releases. Each recommendation will be or has been considered for implementation. In addition, the exercise provided all affected employees with a heightened awareness of safety issues related to the covered processes.