City of Sioux City Water Treatment Plant - Executive Summary |
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APPLICABILITY The Sioux City Water Treatment Plant in Sioux City, IA uses chlorine for disinfection as part of its process to provide quality drinking water to its citizens. Chlorine is purchased in ton cylinders and stored in a special Chemical Feed Building outside the main Water Treatment Plant. At any time, there could be as many as 6 chlorine ton cylinders in the storage room. The building contains local and remote warnings and will automatically close all vests if there is a chlorine leak. It is the intent of the City of Sioux City to investigate reducing the inventory at the plant. Fewer ton cylinders in place at any one time will not only provide a more safe environment, but also lend itself to the "just in time" philosophy of good business practices. ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The City of Sioux City accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practi ces, and is in compliance with all applicable EPA Prevention Program requirements. Chemical-specific prevention steps include awareness of the hazardous and toxic properties of chlorine, presence of chlorine detectors and a chlorine room that will lock-up if there is a chlorine leak. Also the Sioux City Fire Department HazMat team is available in five minutes or less. Material Safety Data Sheet (MSDS) for chlorine is available in compliance with 29 CFR 1910.1200. The current maximum intended inventory of chlorine is 8,000 lb. stored in four one-ton cylinders, and two one-ton cylinders connected to the chlorination system. It is the intent of the City of Sioux City to minimize this amount by January 1, 2000. Operation temperature is always atmospheric. Control of the chlorination process is by flow proportional and residual chlorine feed pacing. Chlorine residual analyzers continuously monitor and record the treated water residuals. Equipment specific ations meet national and state recommendations. The facility was designed and built in conformance with the following Codes and Standards: Equipment Code/Standard Electrical National Electrical Code (NEC) Piping American Society of Mechanical Engineers/American National Standards Institute (ASME/ANSI) Structures Uniform Building Code (UBC) Ventilation American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) Other General Uniform Fire Code (UFC) Concrete American Society for Testing Materials (ASTM) The chlorination process is designed in compliance with recognized and generally accepted good engineering practices. The operation of the facility adheres to the guidelines of the Chlorine Institute. The City of Sioux City Water Treatment Plant will update this safety informa tion if a major change occurs that makes the information inaccurate. A review of the hazards associated with the chlorine facility process and procedures was performed. Documentation includes the hazards associated with chlorine and the chlorination process; the possibility of equipment malfunctions or human error, and the steps used or needed to detect or monitor releases. All equipment was inspected during the hazard review; it was determined that the chlorination facility was designed, built and operated in accordance with applicable codes and industrial guidelines. The results of the hazard review were documented. The hazard review will be updated at least once every five years. The City of Sioux City Water Treatment Plant will also conduct reviews whenever a major change in the process occurs; all issues identified in the review will be resolved before startup of the changed process. The City of Sioux City Water Treatment Plant has prepared writte n procedures that provide clear instructions or steps for safely conducting activities associated with the chlorination process. They are consistent with the applicable safety information. The following procedures are in the City of Sioux City Water Treatment Plant General operation and Maintenance Manual for Chlorination System: initial startup, normal operations, emergency shutdown and operations, normal shutdown, startup following a normal or emergency shutdown or a major change that requires a hazard review; consequences of deviations and steps required to correct or avoid deviations; and equipment inspections. The City of Sioux City Water Treatment Plant will update these operating procedures, if necessary, whenever a major change occurs and prior to startup of the changed process. The City of Sioux City Water Treatment Plant ensures that each employee presently operating the chlorination process, and each employee newly assigned to this process have been tra ined or tested competent in the operating procedures listed above that pertain to their duties. Refresher training is provided yearly to each employee operating the chlorination process to ensure that the employee understands and adheres to the current operating procedures of the process. This frequency of refresher training was determined by consultation with the employees operating the process. The City ensures that workers are trained in any updated or new procedures prior to startup of a process after a major change. The City of Sioux City Water Treatment Plant has prepared and implemented procedures to maintain the on-going mechanical integrity of the chlorination process equipment. Some procedures or instructions were provided by chlorination process equipment vendors. Each employee involved in maintaining the on-going mechanical integrity of the chlorination process has been trained. To ensure that the employee can perform the job tasks in a safe manner, each employ ee was trained in the hazards of the process, in how to avoid or correct unsafe conditions, and in the procedures applicable to the employee's job tasks. The Water Plant does not commonly use outside maintenance contractors, but the City of Sioux City does verify that any such contractors are trained to perform the required maintenance procedures. The City of Sioux City Water Treatment Plant performs inspections and tests on chlorination process equipment. Inspection and testing procedures follow recognized and generally accepted good engineering practices. The frequency of inspections and tests of process equipment is consistent with applicable manufacturers' recommendations, industry stands or codes, good engineering practices, and prior operating experience. The City of Sioux City Water Treatment Plant will certify every three years (or earlier) that compliance with Program 3 Prevention Program requirement ahs been evaluated to verify that the procedures and practices dev eloped are adequate and are being followed. The compliance audit will be conducted by at least one person knowledgeable in the process. A report will be prepared of the audit findings. An appropriate response to each of the findings of the compliance audit will be promptly determined and documented listing any deficiencies that have been corrected. The Plant will retain the two most recent compliance audit reports within the prior five-year period. The City of Sioux City Water Treatment Plant will investigate each incident which resulted in, or could reasonably have resulted in a catastrophic release. An incident investigation will be initiated as promptly as possible, but not later than 48 hours following the incident. A summary will be prepared at the conclusion of the investigation including: date of incident, date investigation began, a description of the incident, the factors that contributed to the incident, and any recommendations resulting from the investigation. All i nvestigation findings and recommendations will be promptly address and resolved. The findings will be review will all affected personnel whose job tasks are affected by the findings. Investigation summaries will be retained for five years. The City of Sioux City Water Treatment Plant emergency response policy involves the preparation of response plans which are tailored to our local plant, and to the emergency response services available in the community, and is in combine with the EPA Emergency Response Program requirements. The Water Plant is NOT a first responder as there are too few workers to run an appropriate program. The local fire department HAZMAT responds to chlorine accidental releases. However, an emergency response plan is maintained at the stationary source for the purpose of protecting public health and the environment and contains procedures for informing the public and local emergency response agencies about accidental releases in compliance with the local HAZMAT guidelines. The local fire department is a member of the Woodbury County Local Emergency Response Planning Committee (LEPC), and has been involved in developing a community emergency response plan. The Plant will evacuate and call 911 for HAZMAT in an emergency chlorine release. GENERAL INFORMATION All these elements are in place at the Water Plant in at least a rudimentary form. It is the intent of the City of Sioux City to again review these policies and make the necessary improvements in the next six months, which will be by January 1, 2000. TOPOGRAPHY The topography type selected for input into the scenario analysis was urban (terrain with many obstructions). A review of USGS 7.5-minute quadrangle maps of the area shows the water treatment plant is located in the Missouri River valley. A line of bluffs rising 199 plus feet above the valley form a semicircle around the plant from Northwest to the northeast. A series of buildings lie immediately west of th e treatment plant. The Missouri River is approximately 1,000 feet south of the treatment plant and the South Sioux City, Nebraska metropolitan area is approximately 2,000 feet south-southeast. METEROLOGICAL CONDITIONS FOR WORST-CASE SENARIO The meteorological conditions for the worst-case are specified in the RMP regulations as follows: Wind Speed: 1.5 meters/second (3.4 miles/hr) Stability Class: F (very stable conditions) Air Temperature: 25 degrees C (77 degrees F) WORST-CASE RELEASE ANALYSIS The regulations define the worst case release as a catastrophic release in which the total content of the single largest vessel onsite is released to the environment. All of the chlorine storage vessels at the Water Treatment Plant are one ton cylinders. For this analysis, the cylinder was assumed to be outdoors when the release occurs. For toxic substances that are normally gases at ambient pressure, the regulations stipula te the release time frame must be 10 minutes for the worst-case scenario. The toxic endpoint for chlorine is established by the regulation to be 0.0087 mg/L. The endpoint analysis was completed using RMP*Comp software developed by the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA). At a release rate of 200 pounds per minute for 10 minutes directly to the environment, the toxic endpoint for the worst-case scenario is calculated to read a radius of approximately 2.1 kilometers (1.3 miles) around the WaterTreatment Plant. The offsite receptors were determined as follows: Residential Population: Siouxland Interstate Metropolitan Planning Council (SIMPCO) using the U.S. census Bureau LANDVIEW III mapping program. The estimated residential population within the worst-case consequence zone is 550. Public Receptors: A review of the USGS 7.5 minute quadrangle map for the Sioux City area indicates there are schools, hosp itals, public recreation areas, major commercial and industrial areas located within the worst-case consequence zone. Environmental Receptors: A review of the USGS 7.5 minute quadrangle map for the Sioux City area indicates there are no environmental receptors within the worst-case consequence zone. ALTERNATIVE RELEASE ANALYSIS Hazard Review: Chlorine is withdrawn at a valve near the top of the cylinder and it flows via plastic line to a gas regulator. Chlorine is withdrawn from the regulator via a vacuum and is routed to the chlorine injector through approximately 20 feet of 5/8" plastic tubing. If a break occurs at any location within the plastic tubing, the vacuum is lost and all chlorine flow stops. If a break occurs before the regulator, chlorine will escape until mitigation measures can be applied by emergency responders. Based upon the hazard review conducted by facility personnel, the most likely release scenario resulting in offsite consequences would be a break in the cylinder valve. The alternative release scenario assumes the release occurs within the chlorine storage building and that all doors are closed prior to and during the release. The release occurs from the valve located at the top of the cylinder, therefore, only chlorine in the gaseous phase is released. It is assumed the valve partially fails, creating a breach of up to 0.0276 square inches. The release rate for chlorine vapor can be calculated by the following equation provided in the EPA Offsite Consequence Guidance Manual: QR = (190)Ah where: QR = release rate (pounds/minute) 190 = chemical-specific factor for chlorine at a tank pressure of 113 psi Ah = hole area (square inches) Solving: QR = (190) (0.0276) = 5.244 pounds per minute The chlorine storage building is equipped with a chlorine alarm system which will alert plant workers within 30 seconds after a release occurs. Assume the Fire Department is called within 30 seconds of the worker being alerted and that it requires five minutes for the Fire Department to arrive at the Water Treatment Plant. Assume 20 minutes elapses before the Fire Department can successfully patch the leak. Total time frame for emergency actions to be completed is 26 minutes. The toxic endpoint for chlorine is established by the regulation to be a concentration of 0.0087 mg/L of chlorine. The endpoint analysis was completed using RMP*Comp software. At a release rate of 5.244 pounds of chlorine per minute, a 26 minute release would amount to a loss of 162.56 pounds of chlorine. Assuming the release is contained within the chlorine storage building, the toxic endpoint for this release is calculated to reach a radius of approximately 0.2 kilometers (0.1 mile) around the Water Treatment Plant. The offsite receptors were determined as follows: Reside ntial Population: Based upon visual observation of the area included within the alternative release scenario consequence zone, there is no residential population affected. Public Receptors: A review of the USGS 7.5 minute quadrangle map for the Sioux City area indicates a commercial area located within the alternative release scenario consequence zone. Environmental Receptors: A review of the USGS 7.5 minute quadrangle map for the Sioux City area indicates there are no environmental receptors within the alternative release scenario consequence zone. FIVE-YEAR ACCIDENT HISTORY These has been only one accidental release of chlorine in the past five years, occurring August 28, 1995. The release was small and was completely contained in the chemical feed building of the Water Treatment Plant. No one offsite was evacuated, but seven workers at the Plant were evacuated from the Administration/Treatment Building. HAZMAT arrived in less than five minutes from the start of the leak. Once inside the building, HAZMAT closed the valve from the tank; however, the leak actually stopped less than one minute after it began. All notification of public receptors was the responsibility of the HAZMAT team. EMERGENCY RESONSE PROGRAM There are 11 full time workers, one half-time clerk and one seasonal laborer (May to August) at the Sioux City Water Plant. Because there are so few workers, the Water Plant will always rely on the local Fire Department and its HazMat team to provide emergency response. |