Peele-Dixie Water Treatment Plant - Executive Summary
At the turn of this century water borne diseases were a leading cause of death in the United States. Epidemics of typhoid, cholera, dysentery and other water-borne diseases occurred. After chlorine's introduction into public water supplies, deaths from typhoid in the U.S. dropped dramatically from 25,000 in 1900 to less than 20 in 1960. Water-borne disease is even still a leading cause of infant mortality in many countries throughout Asia, Africa, and Latin America where infant mortality rates are 10 to 20 times greater than in the U.S. In the U.S., however, water-borne disease has been virtually eliminated due to an effective public health strategy of utilizing chlorine for drinking water disinfection. Chlorine disinfection is arguably one of the greatest achievements for public health worldwide in the last hundred years and is credited with increasing the life expectancy of Americans by more than 50 percent. Furthermore, public health has benefited from the use of
anhydrous ammonia in water disinfection processes because of the reduction in the formation of disinfection by-products.
However, it is important to recognize that the use of chlorine and anhydrous ammonia is not risk free. Historically it is clear that utilities have recognized the risks and have been successful in developing procedures to handle chlorine safely and to protect the off-site public and the environment from potential accidental releases.
As an added layer of protection, the United States Environmental Protection Agency promulgated Hazardous Chemical Risk Management Program regulations to further ensure that facility owners understand the risks and take proactive efforts to reduce risk through comprehensive training programs, procedures, and risk mitigation measures. Additionally, EPA wanted the public to be informed regarding these issues.
The City of Fort Lauderdale Public Services Department has always understood these risks and has maintained a well-trained staff
and a safely operated and maintained facility. The City's track record is exemplary with respect to handling hazardous chemicals. Furthermore, the City has taken a comprehensive approach to be in full compliance with the RMP regulation by June 21, 1999 and a proactive approach to a public information program which is above and beyond the requirements of the regulation.
The City owns and operates the Peele-Dixie Water Treatment Plant (WTP). The facility's mission is to protect public health by providing our community with safe drinking water, free of harmful pathogens. Approximately 650 pounds per day of chlorine gas and 60 pounds per day of anhydrous ammonia are used to disinfect the water and make it safe for human consumption. A maximum of 16,000 pounds of chlorine and 34,000 pounds of anhydrous ammonia are stored on-site. The chlorine and ammonia are stored as gases that are liquefied under pressure.
CHLORINE PROCESS AND SAFETY EQUIPMENT
The chlorine sys
tem at the Peele-Dixie WTP is a gas feed system. It consists of an outdoor, covered chlorine storage and handling area and an enclosed room containing five chlorinators (chlorine vapor flow control meters). The chlorinators regulate the flow of chlorine vapor as it is fed under vacuum to the various chlorine injection points throughout the plant.
Eight one-ton containers are stored in the chlorine storage and handling area at any one time. Each container is secured in a separate steel cradle to prevent it from moving. The containers are hooked up to two manifolds, four containers per manifold. One manifold is in service at any one time, simultaneously feeding chlorine vapor from four containers. The chlorine containers are hooked up to the manifold through individual 2-foot, 3/8-inch diameter flexible copper tubing. The manifolds that the chlorine feed tubes are hooked up to are constructed of schedule 80 1-inch diameter black steel pipe.
The chlorine gas passes through the ma
nifold to a vacuum regulator, which drops the pressure in the system to a very slight vacuum. As water flows through the injectors, the vacuum created by the pressure differential draws the chlorine vapor from the regulator through the chlorinators and into the injectors. At the injectors chlorine gas is mixed with water to form a chlorine solution. The piping in the vacuum portion of the system is composed of schedule 80 PVC pipe. Should a leak develop in the piping downstream of the vacuum regulator, chlorine would not be released. Instead, air would be drawn into the injectors. In addition, loss of vacuum alarms in the chlorinators would activate.
AMMONIA PROCESS AND SAFETY EQUIPMENT
The Peele-Dixie WTP ammonia system is a gas feed system. The ammonia system operates by feeding gaseous ammonia from one of two above-ground storage tanks. One tank has a capacity of 6,565 gallons while the other can hold 1,415 gallons. A manually operated switchover system allows for switchin
g from one storage tank to the other. Ammonia gas flows under pressure from the storage tank to the vacuum regulator-check unit (VRCU). At the VRCU, the gas pressure is reduced to a slight vacuum.
The vacuum created in the injector assemblies pulls the ammonia gas from the VRCU through the ammoniators (which control the flowrate of the gas) and into the injectors. The ammonia gas is mixed with water in the injectors to form an ammonia solution. The ammonia solution is then fed to the various application points.
The ammonia storage tanks are protected by pressure relief valves and a deluge system. The pressure relief valves are designed to prevent buildup of pressure in the tank (caused by heating from the sun) which could lead to a rupture of the tank. The deluge system is designed to automatically spray water on the tank and cool it if sensors detect a high pressure or temperature in the tank. In addition, the deluge system can be used to mitigate the consequences of a leak b
ecause ammonia gas would readily be absorbed by the water spray.
RISK MANAGEMENT AND PROCESS SAFETY MANAGEMENT PROGRAM OVERVIEW
Chlorine and anhydrous ammonia are subject to the Environmental Protection Agency's (EPA's) Risk Management Program (RMP) regulation which can be found in 40 CFR 68 and the Occupational Safety and Health Administration's (OSHA's) Process Safety Management Program (PSMP) regulation which can be found in 29 CFR 1910.119.
The primary components of the RMP are as follows:
* A five-year accident history
* An off-site consequence analysis for a worst-case and alternative release scenario
* A comprehensive prevention program to minimize risks (i.e. minimize the potential for a release)
* An emergency response program to ensure that an accidental release is appropriately handled
* An overall management program to supervise the implementation of the RMP
Following development of the RMP, the facility must submit a Risk Management Plan (Plan) to t
he EPA by June 21, 1999. The Plan is a summary of the facility's Risk Management Program. The RMP will be updated every five years, or whenever a process changes or a new process is added. The OSHA PSM regulation has basically the same requirements as the prevention program element of the EPA RMP. The Peele-Dixie WTP RMP meets the requirements of both regulations.
The following sections briefly summarize the elements of the RMP.
FIVE-YEAR ACCIDENT HISTORY
The Peele-Dixie WTP has used chlorine to disinfect water since 1927. Ammonia has been used in the disinfection process since 1983. In the last five years, the facility has had no accidental releases, which were required to be reported under the RMP regulation.
WORST-CASE RELEASE SCENARIO
The worst case release scenario for a toxic gas has been defined by the EPA to be an accidental release in which the largest on-site vessel, containing the regulated chemical, releases its contents as a gas over ten minutes. Since the facili
ty's largest chlorine and ammonia containers store 2,000 pounds and 27,900 pounds respectively, the worst case release scenarios are a release of 2,000 pounds of chlorine and 27,900 pounds of ammonia over 10 minutes. These scenarios were modeled using RMP*Comp software to estimate the distance to an endpoint of 3 parts per million (ppm) for chlorine and 200 ppm for ammonia.
ALTERNATIVE RELEASE SCENARIO
The alternative release is a "more likely" incident than the worst-case. The RMP regulation allows the owner to define the alternative release scenario based on historical experience or operations staff knowledge of their system. The alternative scenario for the chlorine was to assume that the pigtail (i.e., the flexible tubing connecting the chlorine container to the piping manifold) disconnected from the chlorine container valve. The alternative scenario for the ammonia was to assume that the ammonia gas supply header failed. In addition, it was assumed the excess flow valve in
the ammonia storage tank mitigated the release rate. These scenarios were modeled using RMP*Comp software to estimate the distance to an endpoint of 3 ppm for chlorine and 200 ppm for ammonia.
There are always inherent risks associated with handling and using chlorine. These risks include the potential inhalation of chlorine gas if it is accidentally released. The prevention program is a key component to reducing the risk associated with a potential chlorine gas release. Key elements of the prevention program include:
* Employee participation
* Process safety information
* Process hazard analysis
* Incident investigation
* Standard operating procedures
* Mechanical integrity
* Management of change
* Pre-startup review
* Compliance audits
* Hot work permits
* Trade secrets
The following briefly states the benefits of the following prevention program elements: standard operating proce
dures, mechanical integrity program, employee training and the process hazard analysis.
The facility staff has developed up-to-date and accurate written standard operating procedures (SOPs) to ensure that operators have clear instructions for safe operation of the chlorine and ammonia systems. Effective SOPs, when combined with operator training, are instrumental in ensuring safe operation of the system and in preventing accidental releases.
The purpose of the mechanical integrity program is to ensure the continued integrity of the process equipment. An effective mechanical integrity program is integral to preventing accidental releases that may result from mechanical failure of improperly maintained equipment. The Peele-Dixie WTP's mechanical integrity program includes maintenance, inspection, and testing procedures and schedules along with maintenance personnel training.
Knowledgeable well-trained personnel are essential to preventing and mitigating the effects of accidental c
hemical releases. The Peele-Dixie WTP's training program ensures that personnel working on or near the chlorine and ammonia systems are adequately trained in operation and maintenance procedures and the appropriate response actions to an accidental release.
The process hazard analysis is a valuable risk reduction tool that outlines deficiencies in equipment and procedures, identifies potential system failure modes, and provides recommendations for system and operational improvements.
EMERGENCY RESPONSE PROGRAM
A comprehensive emergency response program has been prepared which outlines the procedures and lines of communication that are necessary to effectively respond to and mitigate a potential chlorine or ammonia release. The facility emergency response program includes procedures for notifying the local hazardous materials (hazmat) teams of the incident and procedures for evacuating the facility. There are four local hazmat teams in Broward County that can respond to mitigate an
accidental release. Facility staff have coordinated with the local fire department to ensure that they are fully trained and equipped to quickly respond to an incident. Peele-Dixie WTP staff will practice the emergency response procedures in an annual training drill.
PLANNED CHANGES TO IMPROVE SAFETY
The City of Fort Lauderdale Public Services Department has undertaken a study to review the costs and qualitative issues of changing to an alternative (i.e., safer) disinfection system. The chlorine alternatives being evaluated include switching to on-site generation of sodium hypochlorite (at 0.8% concentration) and purchasing bulk hypochlorite (at 12% concentration). In addition, these alternatives will be compared to staying with chlorine gas and enclosing the existing facilities (to contain a chlorine leak) and adding an emergency chlorine scrubber. The anhydrous ammonia alternatives being evaluated include switching to using ammonia solution or staying with anhydrous ammonia and
enclosing the existing facilities (to contain an ammonia leak) and adding an emergency ammonia scrubber. The results of this report will be used to assist in planning for future safety improvements. The results of this study were not available at the time this report was prepared.
In addition to this study, City staff intend to install additional leak detectors and local audible and visual alarms at all chlorine and ammonia storage locations.