Sioux Falls Water Reclamation Plant - Executive Summary
Executive Summary |
Chemicals are widely used in industry, in the home, and in the environment and are an integral part of everyone's daily lives. They are transported on roads, water, and railways. The City of Sioux Falls Water Reclamation Plant uses chemicals, too. The plant uses chlorine to disinfect our reclaimed water to discharge safe water to the environment. The natural world contains more that 1,500 chlorine-containing compounds. Human cells generate hypochlorite, a form of chlorine to fight infection. Chlorine purifies our drinking water, disinfects our swimming pools and is truly life saving. In fact the World Health Organization estimates that 25,000 children worldwide die every day from waterborne diseases resulting from the lack of a water disinfection agent such as chlorine.
Storing chemicals can be a hazard. We take our safety obligations in storing and using chemicals as seriously as we take providing the environment safe disinfected water. The f
ollowing document describes what could happen if there were to be an accident, the steps we take everyday to ensure that our plant operates safely, and what we do in the event of an emergency.
The USEPA's Clean Air Act Amendments of 1990 included provisions that require facilities that use certain substances to develop a formal plan to reduce the likelihood of an accidental release of the substances to the atmosphere and reduce the likelihood of serious harm to the public and the environment. Before these regulations were in place, the Sioux Falls Water Reclamation Plant had already established many of the components of the plan. The requirements of this plan, commonly referred to as a Risk Management Plan (RMP), are detailed and codified in 40 CFR Part 68.
The City of Sioux Falls Water Reclamation Plant stores chlorine and digester gas (methane) in quantities above the regulatory thresholds at which a RMP is required. Digester gas is a byproduct of the biosolid
s stabilization process and consists of primarily methane and carbon monoxide. Methane, which is also known as natural gas, is what is commonly used in homes for heating. The plant's digester gas is also used for co-generation of electricity and other uses. Because a fire or explosion of digester gas does not present a risk to anyone located outside of the plant, the regulations do not require that a detailed RMP be completed for digester gas. However, the plant does follow safe work practices to minimize the chances of a release of digester gas.
Chlorine Process Safety Systems
The Water Reclamation Plant stores chlorine in 1-ton containers. Chlorine is mixed with the treated, reclaimed water prior to discharging it to the Big Sioux River. Chlorine is non-explosive and non-flammable, however, like oxygen it is capable of combustion under some circumstances. In addition, it is an irritant to the respiratory system, eyes and skin. Exposure through inhalation at high concentrations is
toxic. To prevent accidental releases from occurring that may cause these injuries, the Water Reclamation Plant has several safety systems. These systems along with the Prevention Program described below greatly reduce the possibility of a significant release of chlorine from occurring. One safety system is the chlorine "leak detectors" that continuously monitor for leaks in the chlorine storage area. Even the smallest of leaks activates alarms that immediately alert plant personnel and allow them to prevent a potential release of chlorine to the atmosphere. In addition, sensors monitor the system pressures and temperatures to detect abnormal conditions that may indicate that a chlorine leak is about to occur. These monitors allow corrective actions to be taken before a leak may occur.
To date, the safety systems in place have allowed the Water Reclamation Plant to achieve an excellent record in preventing accidents. No chlorine release causing a safety or health hazard has occurred
within the last 18 years.
Safety systems help reduce or eliminate the consequences of an accident, much like seat belts reduce injuries in car accidents and anti-lock brakes help avoid car accidents. But, unfortunately accidents can occur. By being prepared for an accident, we can handle the situation in a way that protects those around us. At the Water Reclamation Plant they prepare for an accidental release by planning a course of action to address and handle the situation. The Emergency Response Program details appropriate courses of action to be taken in the event of a release and is designed to protect people inside as well as outside of the plant. The combination of safety systems and the Emergency Response Program greatly reduces the risk due to a potential accidental release for people inside and nearby the plant.
Components of the RMP
The RMP consists of three major parts. The first part is the Hazard Assessment. The Hazard Assessment is done to determine the effects th
at a release of a regulated substance could have on the public. The second part is a Prevention Program that consists of 7 elements designed to improve the system safety and decrease the likelihood of a release. The third part is the Emergency Response Program, which develops a plan for dealing with a release in the unlikely event that one would occur.
A Hazard Assessment was performed to determine the effects a release would have on the public. For chlorine, the distance a set concentration of chlorine would travel must be determined. For digester gas, the effects of an explosion must be determined. In addition, an estimate of the population outside of the plant boundary that could be impacted was determined, and sensitive receptors such as hospitals, schools, and parks were identified. The Hazard Assessment considers two release scenarios-a "worst case" and an "alternative release."
If a release were ever to occur, the gas would migrate as the wind pushes it in t
he prevailing wind direction. The wind would move the gas in primarily one direction. But the regulations view the release as thought it would spread in all directions. In other words, the distance determined by the Hazard Assessment is only valid for the direction of the wind. Someone located the same distance upwind would not be affected by the release.
The regulations require the development of a worst-case release scenario based on conservative assumptions. For example, it is required to assume that the entire contents of the largest single container of chlorine will be released over 10 minutes. This is unlikely to occur because the physical properties of chlorine would cause the chlorine to actually freeze over. The frozen chlorine must then thaw to release further chlorine to the atmosphere. This freeze-thaw cycle would slow the release. Because of the freeze-thaw cycle the distance the chemical would travel is shorter than predicted. In addition,
the regulations require that active efforts to stop the release cannot be considered. In many scenarios active efforts to stop the release would reduce the amount released. The regulations also require that the worst-case scenario assume conservative atmospheric conditions that result in a larger area of impact.
The hazard assessment requires that the "toxic endpoint" or distance from the point of release to a location at which the chemical concentration equals or exceeds a certain concentration must be determined. That concentration is defined as the maximum airborne concentration below which individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects, or symptoms that could impair an individual's ability to take protective action. Because the cloud from a chlorine leak would disperse relatively quickly, an individual at the worst-case scenario distance would be exposed to the exposure limit concentration for much less
than the 1 hour assumed by the limit. In addition, the exposure limit concentrations result in relatively minor health effects. Therefore, an individual at the worst-case scenario distance would be affected less than the results of the worst-case scenario may imply. Using these assumptions, computer modeling estimated that the distance to the toxic endpoint would be 1.04 miles.
For the digester gas worst-case scenario, it must be assumed that all the gas in the vessel containing the largest quantity of digester gas is catastrophically released, and the gas is ignited and explodes. This is very unlikely to occur since the proper mixture of methane and oxygen required for an explosion would be difficult to achieve. The distance to the end of the impact zone for a digester gas explosion is defined by "1-psi overpressure." The 1-psi overpressure is the outside of the explosion shock wave, along which broken glass and other similar structural damage is possible. Calculations showed that fo
r digester gas even the impacts of a worst-case scenario explosion would only travel 773 feet and not impact anyone outside of the plant boundary.
The RMP rule also requires that at least one alternative release scenario be evaluated. The alternative scenarios reflect a type of release that is more likely to occur compared to the worst-case scenario. Unlike the worst-case scenario, the alternative release scenario may consider active actions to stop or contain the release and a more realistic release quantity and release rate. Lastly, it assumes local, typical meteorology, which is more realistic than the conservative meteorological conditions that must be assumed for the worst-case scenario. The alternative release scenario for chlorine was a release of chemical through a vacuum regulator relief valve. The alternative release scenarios are considered to be more representative of the effects likely in the event of a release. The distance that the alternative releas
e of chlorine would travel was estimated to be 0.07 miles.
The Prevention Program consists of 7 elements designed to improve the system safety and decrease the likelihood of a release.
The RMP regulations require that information concerning process chemicals, technology, and equipment be compiled as part of a RMP program. Emergency response planners can use such information to develop training programs and procedures, or as a general resource. The information will be supplied to contractors who will work in the chlorine process area. All the required process safety information was compiled as required by the RMP regulations. The information meets and in many cases exceeds the minimum required by the regulations.
A hazard review was conducted systematically to evaluate potential causes and consequences of accidental releases. This information was used by Water Reclamation Plant staff to improve safety and reduce the consequences of acc
idental releases. The chlorine Hazard Review was conducted by CH2M HILL with the assistance of Water Reclamation Plant staff familiar with the process operation and maintenance and plant management. The review was done using a "Checklist" method. Based on the results of the review, numerous changes in operating, maintenance, and other process safety management procedures that would improve the overall safety of the chlorine system were identified. The changes that most effectively help prevent an accidental release have been or are scheduled to be implemented.
Operating procedures for the chlorination processes have been developed. Written operating procedures assure continuous, efficient, and safe operation of the facility. The goal of the operating procedures is to provide clear instructions to safely operate the process. Operating procedures are also used to train new employees and to provide refresher training for existing staff.
The detailed operating procedu
res include startup, shutdown and emergency operating procedures. The procedures describe how the system should be operated in order to minimize the chances of an accidental release. The procedures also emphasize safety considerations during operation and address hazardous situations that can occur and how to correct them.
An effective RMP training program can significantly reduce the number and severity of accidental release incidences. Employees involved in operating or maintaining the chlorination process receive training that includes applicable operating and maintenance procedures and an overview of the process. Training must emphasize safety and health hazards and safe work practices.
Sioux Falls Water Reclamation Plant staff received training in accordance with regulatory requirements as part of the City's training program. Sioux Falls Water Reclamation Plant staff also receive annual training on chlorine hazard awareness and emergency response. Refresher process operat
ion and maintenance training is provided at least every 3 years.
An effective maintenance program is one of the primary lines of defense against a release. The maintenance program also addresses equipment testing and inspection, preventative maintenance schedules, and personnel training. The intent is to ensure that equipment used to process, store, or handle chlorine is properly maintained and installed to minimize the risk of releases.
The Water Reclamation Plant staff use a computerized maintenance management system Database MP2 to store equipment information, generate and prioritize work orders, schedule preventative maintenance (PM), and maintain an inventory of parts and materials. In addition to preventative maintenance, the Water Reclamation Plant staff performs corrective maintenance in the event of equipment malfunction or breakdown. Selected maintenance staff are trained to properly and safely perform maintenance on the chlorine system.
ch incident that resulted in or could reasonably have resulted in a catastrophic release of chlorine must be investigated. A process to identify the underlying causes of incidents and implement procedures for preventing similar events has been developed. To investigate an incident, an investigation team will be established. As part of the investigation, an incident report will be prepared to recommend system changes to prevent the incident from occurring in the future.
The investigation team should ask questions such as what equipment failed, which behavior failed, and which material leaked, reacted, or exploded? As part of the incident review, staff actions that may have contributed to the incident will also be reviewed. A determination will be made as to whether it is necessary to institute additional training for the employees to prevent the incident from occurring in the future. The incident investigation report and any changes resulting from the report will be reviewed with all st
aff members who operate and maintain the applicable system.
The Water Reclamation Plant will contract out a complete compliance audit for the RMP program at least once every 3 years. The primary goals of conducting a compliance audit are to verify compliance with RMP requirements and good process safety practices, identify process safety deficiencies and develop corrective actions, and increase safety awareness among plant staff.
The compliance audit methodology is modeled after OSHA's guidelines for conducting regulatory PSM compliance audits: Compliance Guidelines and Enforcement Procedures, OSHA Instruction CPL 2-2.45A (September 28, 1992). An auditor knowledgeable in the covered processes, RMP requirements, and audit techniques will conduct the audits. Based on the results of the audit, the plant will promptly determine an appropriate corrective action for each deficiency identified during the audit.
Emergency Response Program
The Emergency Response Program develo
ps a plan for dealing with a release. EPA RMP regulation 40 CFR 68 Subpart E require that an Accidental Release Emergency Response Plan be prepared. The plan must be prepared in accordance with the provisions of another overlapping OSHA regulation-Employee Emergency Plans (29 CFR 1910.38(a)). The Emergency Planning and Response Plan described in this section complies with the requirements of 40 CFR 68.95 and 29 CFR 1910.38(a).
The Emergency Planning and Response plan provides specific emergency response procedures for accidental releases of chlorine. The emergency response procedures cover a release from the initial alarm stage through contacting Hazmat responders. As part of the emergency response procedures there are plans for victim rescue, and communication with responding agencies. In addition, critical plant operations are identified to insure that, if possible, the critical Water Reclamation Plant functions are kept operational.
The Emergency Planning and Response plan also ad
dresses plant site communication, emergency response equipment, first aid and medical treatment, plant evacuation, and emergency response drills.