South District Wastewater Treatment Plant - Executive Summary |
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EXECUTIVE SUMMARY Chlorine is the most commonly used substance for disinfecting treated wastewater. The Miami-Dade Water & Sewer Department (MDWASD) South District Wastewater Treatment Plant (WWTP) also uses chlorine (for chlorination) for disinfecting treated wastewater for in-plant use. Storing and handling large quantities of chlorine can create hazardous situations. The South District WWTP takes safety obligations in storing and using chlorine as seriously as it takes care in treating wastwater. The South District WWTP chlorine handling process is subject to the U.S. Environmental Protection Agency (EPA) Risk Management Program Rule and is a Program 3 process. This regulation requires submission of a Risk Management Plan (RMP). The South District WWTP also produces digester gas and stores it for on-site use as fuel. The maximum quantity of digester gas stored at a given time exceeds the RMP threshold quantity, however, the digester gas process qualifies as a RMP Program 1 p rocess. 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. * Offsite 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 South District WWTP chlorination system and the digester gas system, as required, is provided below. Accidental Release Prevention and Emergency Response Policies The MDWASD accidental release prevention policy involves a unifie d 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 available in the community, and is in compliance with the EPA Emergency Response Program Requirements. South District WWPT has prepared an Emergency Response Plan for Hazardous Materials to facilitate coordination and emergency planning with offsite response officials and facilities in the event of an emergency. South District WWTP has an excellent record in preventing accidents from occurring. General Facility and Regulated Substance Information The MDWASD South District W WTP is located at 8950 SW 232 Street, in Goulds, Florida. The South District WWTP is bounded to the North by SW 232nd Street, to the South by the Black Creek Canal, to the West by SW 97th Avenue, and to the East by SW 87th Avenue. The South District WWTP is located within the 10-mile radius evacuation zone of the Turkey Point Nuclear Power Plant. The facility currently stores and uses chlorine, a regulated toxic substance under the EPA rules. Chlorine is delivered in one-ton containers to the South District WWTP chlorine building. The chlorine building is divided into a covered chlorine storage area and a chlorinator room. The one-ton containers contain liquid chlorine under pressure. The chlorine building is equipped to store up to 20 (containers) tons of chlorine. The maximum quantity of chlorine present at the South District WWPT at any given time exceeds the listed threshold quantities in the EPA rules. It also exceeds the listed threshold quantities in the federal Occupation al Safety and Health Administration (OSHA) Process Safety Management (PSM) Standards. The pressure from the chlorine container forces liquid chlorine through the tubing and into the manifold system. Downstream of the manifold system there is a pneumatically actuated automatic shut-off valve. The valve will also close automatically (or manually) when the chlorine sensor senses a leak. The liquid chlorine flows through the automatic shut-off valve to the evaporators. At the evaporators the liquid chlorine is heated and converted into chlorine gas. The gas then flows from the evaporator through the temperature actuated control valve and the vacuum regulator to the chlorinator. 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 solution that flows through piping to various injections points in the treatment process. The South District WWTP is also provided with a number of safety features to protect the employees and the surrounding community. The two important safety features are (1) automatic shut-off valves and (2) chlorine leak detection and alarm system. The automatic shut-off valves are located immediately downstream of the chlorine containers. Therefore, if a leak occurs anywhere in the system the chlorine source can be isolated and the flow of chlorine can be stopped. The automatic shutoff valves are operated either automatically due to the detection of chlorine leak by the chlorine sensors or manually by pushing a switch. Emergency shutoff switches are located inside the chlorine storage room and in the chlorinator room. The leak detection system consists of chlorine gas sensors located in both the chlorinator room and the storage area. The leak detection system is set to activate the alarms and safety processes when a chlorine concentration of 0.5 ppm or higher is detected. When the leak detection system detects a leak, audible and visual alarms (both local and in the control room) are activated and the automatic shut-off valves closed. The sludge handling process at the South District WWTP consists of a sludge pump station where the sludge is pumped from the secondary clarifiers to the gravity sludge concentrators. Thickened sludge is pumped to two-stage anaerobic digesters for stabilization. The gas produced by the digestion process is compressed, scrubbed to remove hydrogen sulfide, and stored on-site in two 16,500 pounds compressed gas spheres. The digester gas is used to power engine driven blowers and electric generators. Waste heat from the gas power engines is used to heat the primary digesters. A perimeter fence and locked security gates surround the South District WWTP. The plant operates three shifts with employees onsite 24 hours per day, 365 days per year. The South District WWTP is provided with a backup emergency power generator that supplies power for 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 as a gas 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 worst-case release scenario for flammable substances. In addition, alternative release scenario analysis is not required for Program 1 processes. Therefore, no alternative release scenario analysis was performed for the digester gas process, since it is a Program Level 1 process. Chlorine is the o nly regulated toxic substance stored and handled at the South District WWTP, which is subject to the Program 3 RMP rule. 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 South District WWTP is the rupture of a single one-ton chlorine container resulting in the release of 2,000 pounds of chlorine over a 10-minute duration. There are no passive or administrative controls at the South District WWTP for the chlorine storage containers; thus, the chlorine release rate will be 200 lb./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 Respons e 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 release scenario analysis. The results of the dispersion analysis indicated that the worst-case release scenario has offsite impacts. Digester gas containing methane is the only regulated flammable substance stored and handled at the South District WWTP, which is subject to the Program 1 RMP rule. Thus, digester gas 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 South District WWTP is the ru pture of one digester gas sphere of diameter of 60 feet resulting in the release of 11,649 pounds of digester gas. There are no passive or administrative controls at the South District WWTP for the digester gas storage spheres. The released digester gas is assumed to form a vapor cloud and a detonation occurs. A yield factor of 10 percent of TNT-equivalency model is used to determine the distance to the endpoint. The distance to the endpoint is defined as the distance over which a minimum pressure of 1 psi occurs from the pressure wave formed by the detonation. The distance to the endpoint was estimated using the EPA's RMP*Comp software (version 1.06). No public receptors were identified within the flammable endpoint distance for the worst-case release scenario. RMP rules, for Program 3 processes, 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 , unless no such scenario exists. 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 must consider the facility accident history and/or failure scenarios identified in the process hazard analysis. A review of the past five-year accident history data for the chlorination facility pursuant to these rules indicated that there were no chlorine releases, which could have resulted in offsite (outside the South District WWTP boundary) toxic endpoint distances. Similarly, no credible accident scenario was identified from the process hazard analysis, which would reach offsite. Thus, an acceptable/credible alternative release scenario had to be selected based on expert judgement. The alternative release scenario selected involves the release o f chlorine from a pigtail (1/4" diameter) rupture, which occurs during the connection of the chlorine container to the chlorination process. The normal response of the operator is to shut-off the container valve. However, the operator may become incapacitated, leaving the valve open. It is assumed that approximately 15 to 30 minutes would be required for the emergency response team to respond to the accident. In the meantime, all of the chlorine in the container would have been released. The chlorine release rate from the one-ton container was estimated at 150 pounds per minute; thus, the whole container would be emptied in about 13 minutes. 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 alternative release scenario toxic endpoint distance was also estimated using the RMP*C omp (version 1.06) software. 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 dispersion analysis indicated that the alternative release scenario has offsite impacts. Finally, no chlorine or digester gas releases that could have caused safety or health hazard (no deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at the South District WWTP during the last five years. Summary of the Accidental Release Prevention Program and Chemical-Specific Prevention Steps EPA RMP rule does not require the details of Prevention Program for Program 1 processes. Thus, the prevention program details for only the chlorine system are provided below. South District WWTP is in compliance with Federal and State Process Safety Management requirements. South Dis trict WWTP 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 methane, presence of chlorine and methane detectors and alarms, and remotely controlled shutoff device on the chlorine storage. Process and Chemic al 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. This information includes chlorine background information and MSDS sheets. Equipment safety information was meticulously compiled on the chlorine process. Specifications for chlorine process 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 Analysis (PHA) was conducted for chlorination system equipment and procedures. To further assess the integrity of the chlorine system for the preparation of this RMP, a chlorine system checklist was used to assess the overall general condition of the chlorine system operation and maintenance, including human factors that affect personnel performance and system integrity. The PHA will be updated again within a five-year period or whenever there is major change in the process. A list of recommended actions were developed to further improve the chlorine safety and staff is currently evaluating these recommendations. Staff will document the completion of recommended actions. Operating Procedures MDWASD South District WWTP has prepared written operating procedures that provide clear instructions or steps for safely conducting activities relating to chlorination process. They are consistent with the chlorine Process Safety Information. Written operating procedures include: initial startup, normal operations, emergency shutdown, normal shutdown, and start up after emergency shutdown. In addition, South District WWTP developed Standard Operating Procedures (SOPs) for the following steps in the chlorination process: receipt o f chlorine delivery, loading and unloading chlorine cylinder, chlorine cylinder change, and startup after chlorine cylinder change. 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 equipment, and reconfiguration of the facilities. Training South District WWTP employees presently involved in operating or maintaining the chlorine process are trained in an overview of the process and detailed applicable operating and maintenance procedures. South District WWTP ensures that each employee newly assigned to the process, is trained and tested to be competent in the operating procedures listed pertaining to their duties. Each employee (presently involved in operating the chlorine process) has been trained to receive the required knowledge, skills, and abilities to safely carry out the duties and responsibilities, including chlorine emergency response, as provided in the operating procedur es. 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 South District WWTP 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 South District WWTP 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 the training. Contractors MDWASD South District WWTP has procedures and policies in place that specify the information required to be provided to the contractors performing work on the chlorination process, the training requirements for contractor employees, and mechanism to obtain assurance from contractors that they have informed their e mployees of the appropriate safety rules. MDWASD South District WWTP 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 South District WWTP 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 process that requires a MOC procedure implementation. Hot Work Permits and Management of Change The South District WWTP requires employees and contractors to employ safe work practices when performing "hot work" in, on, or around the covered process. The South District WWTP uses a permitting program to ensure hot work is conducted safely on or near a process involving chlorine. 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 South District WWTP 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. Incident Investigation The South District WWTP 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, reco mmendations 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 No chlorine releases that could have caused safety or health hazard (deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at the South District WWTP during the last five years. Emergency Response Program Summary The South District WWTP is a first responder, plant employees respond to chlorine or digester gas 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 a chlorine release. As part of the emergency response program, the South District WWTP has developed and implemented an emergency response plan for the purpose of protecting public health and the environment. The em ergency 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 digester gas response flow chart, responsibilities of various personnel at the facility, duties of on-scene incident commander, site response team, 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 digester gas process. Planned Changes to Improve Safety Numerous changes to improve safety (recommended actions) were previously identified for the chlorine process in 1997 for chlorination system equipment and procedures, when a Process Safety Management (PSM) Plan was performed. All of these recommended actions have been evaluated for implementation as required. |