Alexander Orr Water Treatment Plant - Executive Summary
EXECUTIVE SUMMARY |
Chlorine is the most commonly used substance for disinfecting drinking water. The addition of chlorine or chlorine compounds to water is called chlorination. Chlorination is considered to be the most important process for preventing the spread of water borne disease in drinking water. There are two methods of chlorination, breakpoint chlorination and chloramination. The breakpoint chlorination process consists of adding enough chlorine to the water to satisfy the chlorine demand so that free available chlorine residual can be measured. Chloramination is the process of adding chlorine and ammonia to water, which produces a mono-chloramine residual. The chloramination process lowers the trihalomethane levels in the finished water.
The Miami-Dade Water & Sewer Department (MDWASD) Alexander Orr Water Treatment Plant (WTP) uses chlorine and ammonia for disinfecting and lowering the trihalomethane levels in the finished drinking water to protect public health per stat
e and federal water quality standards. Storing and handling large quantities of chlorine and ammonia can create hazardous situations. The Alexander Orr WTP takes safety obligations in storing and using all chemicals, including ammonia as seriously as it takes care in providing safe drinking water.
The Alexander Orr WTP chlorine and ammonia handling processes are subject to the U.S. Environmental Protection Agency (EPA) Risk Management Program Rule. This rule requires submission of a Risk Management Plan (RMP). An integral part of the RMP is a summary of policies and procedures followed to safely operate the facility, including a description of the possible consequences in case of an accident and the actions, which will be taken, by the facility in an event of an emergency.
The following information is specifically required in the RMP Executive Summary:
* Accidental release prevention and emergency response policies.
* General facility and regulated substances information.
ffsite consequence analysis results.
* Summary of the accidental release prevention program and chemical-specific prevention steps.
* Five-year accident history summary.
* Emergency response program summary.
* Planned changes to improve safety.
The above information for the Alexander Orr WTP chlorine and ammonia systems are provided below.
Accidental Release Prevention and Emergency Response Policies
The MDWASD accidental release prevention policy involves a unified approach that integrates proven technology, trains staff in operation and maintenance practices, and uses tested and proven management system practices. All applicable procedures of the EPA's Prevention Program are adhered to, including key elements such as training, systems management, and emergency response procedures.
The MDWASD emergency response policy involves the preparation of emergency response plans for hazardous materials which are tailored to each facility and to the emergency response services availa
ble in the community, and is in compliance with the EPA Emergency Response Program Requirements. Alexander Orr WTP has prepared an Emergency Response Plan for the treatment plant to facilitate coordination and emergency planning with offsite response officials and facilities in the event of an emergency.
General Facility and Regulated Substance Information
The MDWASD Alexander Orr WTP is located at 6800 SW 87th Avenue (Galloway Rd.) in the center of Miami, Florida. The plant is bounded by SW 64th Street (Hardee drive) to the North and by SW 72nd Street (Sunset Dr.) to the South. Alexander Orr WTP covers 68 acres. The facility stores chlorine and ammonia, which are regulated toxic substances under RMP rule.
Alexander Orr WTP has two chlorine facilities designated as the Old Plant 1 and the New Plant 2. Chlorine is delivered in 90-ton rail cars to chlorine car enclosure. The 90-ton rail cars contain liquid chlorine under pressure. The chlorine system currently supplies a total
of approximately 4500 pounds per day to Plant 1 and 2900 pounds per day to Plant 2. The maximum quantity of chlorine present at the Alexander Orr WPT at any given time exceeds the listed threshold quantity in the EPA rule. It also exceeds the listed threshold quantity in the federal Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) Standard.
The pressure from the rail car forces the liquid chlorine through the tubing and into the feed line. Downstream of each tubing/feed line connection, there is a pneumatically actuated shut-off valve. Pushing one of the shut-off switches manually closes the shut-off valves. The liquid chlorine flows through the shut-off valves to the evaporators in each of the chlorine rooms. At the evaporators the liquid chlorine is heated and converted into chlorine gas. The gas then flows from the evaporator through another automatic shut-off valve, a strainer, a pressure regulating valve, a temperature actuated control val
ve, and a vacuum regulator, to the chlorinators. The chlorinators are used to control the feed rate of the chlorine gas. The chlorinators are equipped with a gas rotameter and a v-notched orifice for controlling the feed rate. Injection of the chlorine into the plant water produces the concentrated chlorine solution that flows to the various injection points in the treatment process.
The Alexander Orr WTP chlorine system is also provided with a number of safety features to protect the employees and the surrounding community. The two important safety features are (1) shut-off valves, and (2) chlorine leak detection and alarm system.
The shut-off valves are located immediately downstream of the chlorine rail cars and in the chlorinator rooms. Therefore if a leak occurs anywhere in the system the chlorine source can be isolated and the flow of chlorine can be stopped. The shut-off valves are operated manually by pressing one of the emergency shut-off switches. Emergency shut-off
switches are located outside the chlorine car enclosure and outside the chlorinator rooms.
The leak detection and alarm system is tripped when a chlorine leak is detected. The leak detection system consists of chlorine gas sensors located in both the chlorinator rooms and the chlorine car enclosure. The leak detection system is set to activate the alarms when a chlorine concentration of 0.5 ppm or higher is detected. When the leak detection system detects a leak, audible and visual alarms are activated. When the chlorine alarms are tripped, personnel are restricted from entering the contaminated area without the appropriate protective equipment.
The ammonia system at Alexander Orr WTP includes a primary and an auxiliary ammonia storage tank of a 15,000 gallons capacity each. The ammonia feed system is designed to provide an average dose of approximately 4 mg/L. The amount of ammonia in each tank is determined by means of a float gauge, which is calibrated to report the percent
of the total capacity based on depth of the ammonia in the tank. These tanks are filled up to 80 percent of their capacities. Thus, the maximum quantity of ammonia in a single vessel present at the Alexander Orr WTP will be 12,000 gallons. The maximum quantity of ammonia present at the Alexander Orr WPT at any given time exceeds the listed threshold quantity in the EPA rule. It also exceeds the listed threshold quantity in the federal Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) Standard.
Gaseous ammonia is supplied to the ammoniators from the top of the storage tanks. The ammonia gas flows under pressure through piping through a pressure-reducing valve (pressure regulator) which reduces the pressure to the range of 45 to 55 psig. From the pressure-reducing valve, the ammonia gas then flows through piping to the ammoniators. The ammoniator room houses five direct feed ammoniators each with a feed rate capacity of 1000 pounds per day. Each
ammoniator is equipped with a rotameter and a V-notched orifice for controlling the feed rate manually. Downstream of the ammoniators, the ammonia gas flows into one of two feed pipes for subsequent injection at the desired feed points.
The Alexander Orr WTP ammonia system is also provided with a number of safety features to protect the employees and the surrounding community. The three important safety features are (1) shut-off valves, (2) pressure relief valves, and (3) leak detection and alarm system. The shut-off valves are located on the ammonia storage tanks just downstream of the ammonia supply connection. The valves are actuated by manually pushing the emergency shut-off switch located on the outside wall of the ammoniator room and the outside wall of the chlorine car enclosure.
The pressure relief valves mounted on the storage tanks are equipped with three-way isolating (flapper) valves that can be utilized to isolate one of the two relief valves. The three-way valve a
llows either of the two pressure relief valves to be isolated while the second valve maintains protection for the storage tank.
In addition to the ammonia system components, ammonia vapor sensors are located in the ammoniator room and on the outside wall of the chlorine car enclosure. In the event of a leak, the ammonia sensors activate audible and visual alarms. The alarm set point for the detectors is established at 10 ppm.
A perimeter fence and locked security gates surround the Alexander Orr WTP. The plant operates three shifts with employees onsite 24 hours per day, 365 days per year.
The Alexander Orr WTP is provided with a backup emergency power generator that supplies power to the entire facility.
Offsite Consequence Analysis Results
The offsite consequence analysis includes consideration of two release scenarios, identified as "worst-case release scenario" and "alternative release scenario". The first scenario is defined by EPA, which states that "the owner or operator
shall assume that the maximum quantity in the largest vessel is released over 10-minutes," due to an unspecified failure. The alternative scenario is defined as "more likely to occur than the worst-case release scenario". EPA also requires the performance of one worst-case release scenario for all the regulated toxic substances and one alternative release scenario for each regulated toxic substance used in a covered process.
Chlorine and ammonia are the two regulated toxic substances stored and handled at the Alexander Orr WTP, which are subject to the RMP rule. Since chlorine was estimated to create the greatest distance to a toxic endpoint, thus, chlorine was selected for the worst-case release scenario. Only passive or administrative controls are allowed under this scenario to reduce off-site impacts. The scenario used for the Alexander Orr WTP is the rupture of a single 90-ton chlorine railcar resulting in the release of 180,000 pounds of chlorine over a 10-minute duration.
There are no passive or administrative controls at the Alexander Orr WTP for the chlorine railcars; thus, the chlorine release rate will be 18,000 lbs./min.
The released liquid chlorine is assumed to form a denser-than-air cloud consisting of chlorine vapor and liquid droplets (aerosols) and then disperse in the atmosphere. The distance to the toxic endpoint was estimated using the EPA's RMP*Comp software (version 1.06). The toxic endpoint selected by EPA rules for chlorine is 3 ppm, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). The toxic endpoint was conservatively set by EPA to ensure public notification and that local emergency response planning takes into account the greatest possible impacted area surrounding the release point. EPA-mandated meteorological conditions, namely atmospheric Stability Class F, wind speed of 1.5 meter per second, highest daily maximum temperature (77 deg F), and average relative humidity (50%) were used for the worst-case relea
se scenario analysis. The results of the dispersion analysis indicated that the worst-case release scenario has offsite impacts.
RMP rules require that a scenario which results in offsite toxic endpoint distance and is more likely to occur than the worst-case scenario should be selected as the alternative release scenario for each regulated toxic substance, unless no such scenario exists. The alternative release scenario may also be an actual event, which occurred at the facility. Unlike the worst-case scenario, the alternative release scenario may consider "active" mitigation such as automatic shutoff valves, excess flow valves, and containment with scrubbers. Active mitigation is defined as requiring mechanical, electrical, or human input.
The alternative release scenarios selected for the chlorine and ammonia are summarized below:
The alternative release scenario selected involves the release of chlorine from the flexible hose connecting the railcar to the chlorine process.
This scenario occurs due to the operator using a faulty old flex hose, which results in a crack in the flex hose during the withdrawal of chlorine from the railcar. It is assumed that the crack developed in the 1-inch diameter flex hose equates to a hole of 3/16-inch (0.1875-inch) diameter. The control room would have been warned of the chlorine leak by the chlorine monitors installed at the chlorination facility. It is assumed that approximately ten minutes would be required for operators or an emergency response team to respond and activate the remote controlled shutoff valve. The chlorine release rate for this alternative release scenario was estimated at 87 lb./min. No passive mitigation was considered for the estimation of chlorine release rate. However, human input in closing the shut-off valve was taken into account as an active mitigation, which will reduce the quantity of chlorine released to the atmosphere.
The toxic endpoint distance for the chlorine alternative relea
se scenario was estimated using lookup table from EPA's Water Treatment Plant RMP Guidance document. Toxic endpoint for chlorine is 3 ppm. EPA suggested typical meteorological conditions used were Stability D, wind speed of 3.0 meter per second, average air temperature of 77 deg F, and average relative humidity of 50 percent. The results of the toxic endpoint distance analysis for chlorine indicated that the alternative release scenario has offsite impacts.
The second alternative release scenario selected was for ammonia that involved the release of ammonia from the piping connecting the ammonia storage tank to the process. It is assumed that the hole/rupture that develops in the piping equates to a hole of 5/16-inch (0.3125-inch) diameter. The control room would have been warned of the ammonia leak by the ammonia monitors installed at the facility. It is assumed that approximately ten minutes would be required for operators or an emergency response team to respond and activate t
he remote controlled shutoff valve. The ammonia release rate for this alternative release scenario was estimated at 180 lb./min. No passive mitigation was considered for the estimation of ammonia release rate. However, human input in closing the shut-off valve was taken into account as an active mitigation, which will reduce the quantity of ammonia released to the atmosphere.
The toxic endpoint distance for the ammonia alternative release scenario was estimated using lookup table from EPA's Water Treatment Plant RMP Guidance document. Toxic endpoint for ammonia is 200 ppm. EPA suggested typical meteorological conditions used were Stability D, wind speed of 3.0 meter per second, average air temperature of 77 deg F, and average relative humidity of 50 percent. The results of the toxic endpoint distance analysis indicated that the alternative release scenario has offsite impacts.
Summary of the Accidental Release Prevention Program and Chemical-Specific Prevention Steps
Orr WTP is in compliance with Federal and State Process Safety Management requirements. Alexander Orr WTP accidental release prevention program is based on the following key elements:
* Detailed management system.
* Comprehensive process safety information that is readily available to staff, emergency responders, and contractors.
* Comprehensive preventive maintenance program.
* Performance of process hazard analysis of equipment and procedures with operation and maintenance staff participation and review.
* Use of state-of-the-art process and safety equipment.
* Use of accurate and effective operating procedures, written with the participation of the operators.
* Training of the operators and maintenance staff.
* Implementation of an incident investigation program.
Chemical-specific prevention steps include availability of self-contained breathing apparatus (SCBA), awareness of the hazardous and toxic properties of chlorine and ammonia, presence of chlorine and ammonia dete
ctors and alarms, and remotely controlled shutoff devices on the chlorine and ammonia storage tanks.
Process and Chemical Safety Information
Comprehensive chemical data have been assembled to include regulatory reporting and action thresholds, health hazard, and chemical exposure limitations, as well as detailed physical properties of chlorine and ammonia. This information includes chlorine and ammonia background information and MSDS sheets.
Equipment safety information was meticulously compiled on the chlorine and ammonia processes. Specifications for chlorine and ammonia processes are collected and provided in one place for easy reference. Details such as maximum intended inventory; safe upper and lower temperatures; safe upper and lower pressures; and codes and standards used to design, build, and operate the processes are on file at the facility.
Process Hazard Analysis
In 1997, detailed Process Hazard Analyses (PHAs) were conducted for the chlorine and ammonia systems equ
ipment and procedures. To further assess the integrity of the chlorine and ammonia systems for the preparation of this RMP, checklists were used to assess the overall general condition of the chlorine and ammonia systems operation and maintenance, including human factors that affect personnel performance and system integrity. The PHA(s) will be updated again within a five-year period or whenever there is major change in the processes. A list of recommended actions were developed to further improve the chlorine and ammonia safety and staff is currently evaluating these recommendations. Staff will document the completion of recommended actions.
MDWASD Alexander Orr WTP has prepared written operating procedures that provide clear instructions or steps for safely conducting activities relating to the chlorination and ammoniation processes. They are consistent with the chlorine and ammonia Process Safety Information. Written operating procedures include: initial
startup, normal operations, emergency shutdown, normal shutdown, and start up after emergency shutdown. In addition, Alexander Orr WTP developed Standard Operating Procedures (SOPs) for the following steps in the chlorination and ammoniation processes: receipt of chlorine and ammonia delivery, chlorine car connection and disconnection, transferring car from standby to in-service, and chlorine and ammonia release/spill response. Operating procedures will be developed and put in place prior to any new process equipment coming on line or changes made in the handling of chlorine and ammonia equipment, and reconfiguration of the facilities.
Alexander Orr WTP employees presently involved in operating or maintaining the chlorine and ammonia processes are trained in an overview of the processes and the applicable operating and maintenance procedures. Alexander Orr WTP ensures that each employee newly assigned to the processes, is trained and tested to be competent in the operat
ing procedures listed pertaining to their duties. Each employee (presently involved in operating the chlorine and ammonia process) has been trained to receive the required knowledge, skills, and abilities to safely carry out the duties and responsibilities, including chlorine and ammonia emergency response, as provided in the operating procedures.
Refresher training is provided every three years or less to each employee operating the covered process to ensure that the employee understands and adheres to the current operating procedures. In addition, the Alexander Orr WTP ensures that operators are trained in any updated or new procedures prior to startup of a process after a major change as indicated in their Management of Change procedures.
The Alexander Orr WTP prepares and retains records of initial and refresher training, provides certification of the records, which includes the identity of the employee, the date of training, and the signature of the person (s) administering
MDWASD Alexander Orr WTP has procedures and policies in place that specify the information required to be provided to the contractors performing work on the chlorination and ammoniation processes, the training requirements for contractor employees, and mechanism to obtain assurance from contractors that they have informed their employees of the appropriate safety rules. MDWASD Alexander Orr WTP is required to provide information and explanations concerning the hazards and processes and obtain and evaluate information regarding the contractor's safety program.
Pre-Startup Safety Review and Mechanical Integrity Program
MDWASD Alexander Orr WTP has procedures in place to ensure that a pre-startup safety review is conducted prior to starting up a new covered process or after shutdown event, or prior to starting up modifications to the chlorination and ammoniation processes that require a MOC procedure implementation.
Hot Work Permits and Management of Chang
The Alexander Orr WTP requires employees and contractors to employ safe work practices when performing "hot work" in, on, or around the covered process. The Alexander Orr WTP uses a permitting program to ensure that hot work is conducted safely on or near a process involving chlorine and ammonia.
Internal Compliance Audits
Internal compliance audits will be conducted every 3 years to verify compliance with the programs and procedures contained in the RMP. The Alexander Orr WTP will assemble an audit team that will include personnel knowledgeable in the Risk Management Program rule and in the process. This team will evaluate whether the prevention program satisfies the requirements of the Risk Management Program rule and whether the prevention program is sufficient to help ensure safe operation of the process. The results of the audit will be documented, recommendations resolved, and appropriate enhancements to the prevention program will be implemented.
The Alexander Orr WTP investigates all incidents that could reasonably have resulted in a catastrophic release (serious injury to personnel, the public, or the environment) so that similar accidents can be prevented. An investigation team is assembled and the investigation is initiated within 48 hours of the incident. The results of the investigation are documented, recommendations are resolved, and appropriate process enhancements are implemented. Information found during the investigation is reviewed by affected staff and added or used to revise operating and maintenance procedures.
Five-year Accident History Summary
There have been two accidental releases involving chlorine. These releases occurred on May 16, 1995 and January 5, 1996. The amount of chlorine released was less than one pound from both releases. Valves were the release source from both incidents. Both releases caused on-site injury where the worker inhaled chlorine gas was hospitalized for 24 hours. There
was no off-site impact from either incident. As a result of these accidents additional training classes have been offered on the proper lock out tag out procedures.
Emergency Response Program Summary
The Alexander Orr WTP is a first responder, plant employees respond to chlorine and ammonia accidental releases. Depending on the severity of the accidental release, external resources such as the Metro-Dade Fire Department may be solicited to aid in handling chlorine or ammonia release. As part of the emergency response program, the Alexander Orr WTP has developed and implemented an emergency action plan for the purpose of protecting public health and the environment.
The emergency response plan has been coordinated with local response agencies (Metro-Dade Fire Department). The main elements of the emergency response plan are: (1) chlorine and ammonia response flow chart, responsibilities of various personnel at the facility, duties of on-scene incident commander, site response te
am, and site safety representative, (2) details of emergency recognition and prevention at the facility, (3) procedures for planning and coordination with off-site emergency response organizations, and (4) details of the training program for all employees involved with the chlorination and ammoniation processes.
Planned Changes to Improve Safety
Numerous changes to improve safety (recommended actions) were previously identified for the chlorine and ammonia process in 1997 for chlorination and ammoniation systems equipment and procedures, when Process Safety Management (PSM) Plans were prepared. All of these recommended actions have been evaluated for implementation as required.