Lake Lewisville Water Treatment Plant - Executive Summary |
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The Lake Lewisville Water Production Plant is a water treatment plant that provides drinking water to customers in the area of the City of Denton, Texas. To ensure that our water remains safe throughout the distribution system to every tap, the plant adds a small amount of chlorine as a disinfection agent. The concentrated form of chlorine is liquefied and stored in one ton containers. Before it is mixed with water, chlorine can be extremely hazardous if released to the air all at once. The accidental release prevention and emergency response policies at your facility. The Lake Lewisville Water Production Plant is committed to protecting its employees, the public, and the environment from any accidental releases of hazardous materials used at its facilities. We have implemented safety, environmental protection, and risk management programs to prevent hazardous materials releases. If there is an accidental release, we will immediately call for emergency response, Denton Fire D epartment, to minimize the effect of the release and notify the public of any actions necessary to ensure public protection, through emergency management agencies. The water utility management along with its employees is always looking for ways to improve safety regarding the handling and use of chemicals. In addition to safety, we continuously review operational and maintenance procedures to ensure the process is maintained as safe as possible. The worst-case release scenario(s) and the alternative release scenario(s). OFF-SITE CONSEQUENCE ANALYSIS 1.0 Threshold Quantity Determination at the Lake Lewisville Water Production Plant The regulated chemicals used at the Lake Lewisville Water Production Plant per the "EPA 40 CFR, Article 68-115 Threshold Determination" are chlorine and anhydrous ammonia. Inventory of these chemicals at the production plant is shown in Table 1 below. TABLE 1 Regulated Chemical - Chlorine Maximum No. of Containers - 14 Nominal Weight of Container Cont ents (lbs) 2,000 Maximum Inventory (lbs) - 28,000 According to inventory levels shown in Table 1 chlorine is the only chemical that exceeds the threshold quantity triggering the development of a Risk Management Plan (RMP). The Water Production Plant's handling chlorine is classified as SIC code 4941. Also, the state of Texas is not an OSHA Plan state. Based on these two conditions the water production plant needs to comply with the RMP Program 2 guidelines. The worst-case and alternate-case release scenarios for chlorine complying with RMP Program 2 are discussed below: Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 2 2.0 Determination of Rural / Urban Settings To apply the regulated substance release scenarios, whether the water production plant is in a rural or urban setting must be determined. As defined by the EPA RMP requirements the rural and urban features include the following: URBAN: * Heavy Industrial * Light to moderate industrial * Commercial * Compact Residential RURAL: * Farmland, grassland, large parking lots. The area around the water production plant is a mixture of the rural and urban characteristics and is still developing. Therefore, the City of Denton zoning map was used to determine the setting for the production plant. The zoning data indicates that more than 50% of the area in a 3-mile as well as the 1-mile radius around the production plant will develop as urban property (See Figure 2). Based on this data the setting of the production plant was classified as urban. For the worst-case and alternate-case scenarios, the urban setting was used. 3.0 Worst-Case Release Scenario As required by the EPA/RMP regulations, the worst-case scenario is defined as the release of an entire one ton container of the regulated chemical as a gas in ten minutes. The regulations also require using the worst-case wind speed and atmospheric conditions that result in the greatest projected impact on di stance. For the off-site consequence analysis, the "endpoint" concentration is defined by the Emergency Response Planning Guideline (ERPG-2) values developed by the American Industrial Hygiene Association (AIHA). AIHA defines the ERPG-2 value as "the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action". The endpoint (ERPG-2) value established for chlorine is 0.0087 mg./l or 3 PPM. The American Water Works Association Research Foundation (AWAARF), "Compliance Guidance and Model Risk Management Program for Water Treatment Plants" was used to determine the worst-case scenario impact distance for 0.0087-mg/l endpoint concentration of chlorine. The manual uses results from the Aloha model, which are included in Table 5-1 of the manual. Table 5-1 in the manual for "Scenario ID CL2, worst-case scenario for 1-ton container: Catastrophic failure due to corrosion, impact or construction defects", shows an endpoint distance of 2.6 miles at 770 F for the urban condition. For the temperature range within 880 - 1070 F, a correction factor of 1.0123 was applied to determine an endpoint distance of 2.63 miles for the water production plant. Impact of the worst-case release scenario within the 2.63-mile radius on residential population, public receptors and environmental receptors is shown in Table 2 below. Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 3 TABLE 2 Population Groups Affected Populations Residential Population 43,800 Public Receptors Schools Billy Ryan High School Borman Elementary Calhoun Middle School Denton State School DISD Central Offices Robert E. Lee Elementary Sam Houston Elementary McMath Middle School Sullivan-Keller Childhood Center Thomas Rivera Elementary Hospitals Denton Regional Medical Center Public Recreational Areas Civic Center Park Milam Park Mack Park Fred Moore Park Phoenix Park Martin Luther King Recreational Area Briercliff Park Joe Skiles Park Denia Park South Lakes Park TWU Golf Course Detention Centers Denton County Center for Adult Probation and Detention Center Adult Probation and Juvenile Detention Center Major Commercial, Office or Industrial areas Denton Chamber of Commerce Carroll Courts Building Visual Arts Center City Hall Civic Center Courthouse on the Square Department of Public Safety Texas Workforce Commission Federal Building-Main Post Office Federal Emergency Management Agency Emily Fowler Library South Branch Library Senior Center Texas Women's University University of North Texas Environmental Receptors None Lake Lewisville Water Producti on Plant Risk Management Plan, Executive Summary Page 4 A major release of the magnitude represented by the worst-case scenario is extremely unlikely because of the robust design of the one-ton chlorine containers and the rigorous maintenance and prevention programs at the water production plant. In fact, release reporting databases and water industry experience suggest that the worst-case release scenario as defined in the RMP regulations is so unlikely that it should not be used as the basis for emergency planning. A more reasonable potential release scenario for emergency planning is presented in the alternate-release scenario discussed below. 4.0 Alternate-Release Scenario After site visits, discussions with the plant personnel, evaluation of piping, maintenance practices and chemical release history at the water production plant, a "credible worst-case" scenario was selected as the alternate-release scenario for the water production plant. This alternate-release scenario a ssumes that the flexible tube connecting the 1-ton cylinder to the manifold is completely severed resulting in the release of gas. Table 5-5 and scenario CLA-3 from the AWWARF Guidance Manual was used to determine the end point distance of 0.48 miles for an urban condition. It should be noted that the alternate scenario selected is the worst case condition. The more likely scenario is the possibility of a hole puncture in the flexible line, other than complete severance of the pipe. Also, the effect of building mitigation was not considered although the cylinders are housed in a building with forced ventilation system. This was done to accommodate the remote possibility that a door may be left open. However, for emergency planning purposes the more conservative "credible worst case" for the alternate case scenario was selected. Impact of the alternate case scenario within the 0.48-mile radius on residential population, public receptors and environmental receptors is shown in T able 3. TABLE 3 Population Groups Affected Populations Residential Population 1,000 Public Receptors Schools None Hospitals None Public Recreational Areas None Prisons None Major Commercial, Office or Industrial areas None Environmental Receptors None It should be noted that the entire area within the 0.48-mile radius would not be affected for the alternate case release scenario. Based on the wind direction at the time of the release, a plume will form. The end point and the width of the plume will vary with terrain and weather conditions. Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 5 Accidental Release Prevention Steps The City of Denton is committed to personnel safety, public safety, continued reliable operation and regulatory compliance. Based on this commitment, the Water Production Manager has assumed overall responsibility for the development and implementation of the Risk Management Program. The Plant Manager has also clearly defined accountability and responsibility for each of the prevention program elements to meet both EPA and OSHA Process Safety Management requirements. To ensure a worst-case or alternative release scenario does not occur, the Lake Lewisville Water Production Plant maintains a release prevention program with the primary focus of protecting plant employees and the public from the hazards associated with an accident or release involving chlorine. The multifaceted program includes the use of: * chlorine detectors and alarms to rapidly alert operators to any problems; * process safety information to document the safe process design; * process hazards analyses to evaluate the chemical and process hazards; * operating procedures to ensure that the system is operated safely; * maintenance, inspection and testing to ensure that the system is maintained according to applicable standards and manufacturer's recommendations; * training, hot work permits, contractor safety and employee participation programs to ensure that all employees and contractors working on and around the processes are aware of the hazards, can perform their job duties safely and know the actions to be taken in an emergency; * management of change and pre-startup safety reviews to ensure that changes are documented, analyzed and kept within the design basis; * incident investigation procedure to investigate each incident and "near misses" to determine root causes and make needed safety improvements; * and periodic compliance audits to ensure that our programs are working as they should to protect both employees and the public. Five-Year Accident History Within the past five years, the Lake Lewisville Water Production Plant has not had any accidental releases that resulted in injuries or property damage. The plant has maintained an excellent safety record throughout its operating history and has never had a major chlorine release that could have had adverse effects on the public. Eme rgency Response "In the event that a chlorine release does occur, the Lake Lewisville Water Production Plant has an emergency response program that includes trained onsite emergency responders and coordinates emergency response with the regional response organizations and LEPC. If an emergency did occur, plant personnel would contact the Denton Fire Department response team and notify the regional response organizations who would assist if offsite actions were needed or to help address the chlorine release. " Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 6 The City of Denton will be installing a siren system by January 2000 that will warn the general public of emergencies. This includes sever weather like hail, high winds and tornadoes and hazardous material spills, that could occur anywhere in the city. When the general public hears the alarms, they will either tune their radio to station 88.1 AM KNTU or tune their television to the City of Denton's cable station, Channel 26 for information on the emergency and what actions they should take. All Lake Lewisville Water Production Plant employees are trained for hazard material awareness for first responders. This course is designed to make people aware of their environment and the steps to take if a hazardous material is spilled. Two employees, at the plant, are trained to respond to hazardous material spills to correct problems. If the Lake Lewisville Water Production Plant had an accidental leak, these two employees would assist the Denton Fire Department with technical information to correct major leaks. A chlorine container, specifically designed for training, was purchased and setup to match our system. The two water plant employees, trained for emergency response, along with the Denton Fire Department will take part in training exercises once or twice a year. This training will cover all leak scenarios on a chlorine container. Once a year, all water productio n employees will receive training on our chlorine system and the Risk Management Program. Maintaining A Safe Operation The Lake Lewisville Water Production Plant continually works to safely manage the hazards of chlorine to protect employees, the community and the environment. The Risk Management Program will be maintained to reduce the risk of accidental releases and each year we will conduct training, review procedures, maintain the equipment and follow safe work practices. Periodically, we will audit our program, review our Process Hazard Analysis and coordinate with the community emergency response organization. We will also be assessing further safety enhancements to the facility over the next few years. Chlorine system of the past Safety improvements for the chlorine system began in 1987. A new facility was built that included both inside and outside on-site storage of chlorine containers with an overhead hoist for moving the containers. The new chlorine system is vacuum cont rolled, this reduced the amount of pressurized pipe. Another safety improvement was the addition of chlorine gas detector equipment with audible and visual alarms. Since 1987, additional improvements have occurred to increase chlorine safety. Most of the safety improvements are changes in operational and preventive maintenance procedures. Through safety meetings, independent chlorine safety audits, and general discussions, all of the pressure piping and suspect components were scheduled for replacement every five years. Operators became more aware of potential weaknesses of the system and began to perform routine system checks around the clock. All doors leading from the chlorine system were reconfigured for easy evacuation. A windsock was installed to direct personnel in the event of an accidental leak. In 1995, the chlorine gas detection system was replaced with a more reliable system that is precisely calibrated. Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 7 Current system The current chlorine system is still going through changes to improve safety. With the intense effort to develop and implement a risk management plan, we have found areas that were improved. Procedures that were verbally handed down were written down with improvements. Vital equipment often overlooked was given attention. And training for all personnel on all processes was documented, performed and scheduled. As a part of the Risk Management Program, we wanted to examine the risks associated with the current chlorine feed system or eliminate the risks totally by using non-hazardous chemicals for the disinfection processes. The City of Denton was assisted by Carollo Engineering to determine if our system could reduce or eliminate any hazards associated with its use of gaseous chlorine. The risks associated with storage and use of hazardous chemicals are discussed throughout the RMP. The safety record of the water treatment industry r elative to the use of hazardous chemicals has been very good historically. In some cases, risks can be eliminated; however, usually it is a case of offsetting other risks. There are many different types of risks associated with the storage and use of hazardous chemicals. For purposes of the RMP, they were divided into the following: * Transportation to the site * Unloading of the chemical at the delivery site * Storage of a chemical * Operational procedures for moving containers * Metering and conveying of a hazardous chemical to the application point Metering and conveying risks are by far the most significant associated with the treatment plant. The failure of the flexible connections and lead gaskets seals are the most common cause of chlorine releases followed by valve packing failure and equipment failure. Carollo Engineering concluded that the alternatives to gaseous chlorine all involve significantly greater cost on a present-worth analysis without any risk reduction. Car ollo recommended that we should continue using chlorine in the gaseous form. They also recommended that we purchase emergency shutoff valves for each chlorine container connected to the manifold as a quick means to reduce accidental chlorine leaks. The emergency shutoff valves can quickly close the chlorine container valve in the advent of a leak, thus shutting off the supply of chlorine to the system. This will be done before September 30, 1999. The Self-Contained Breathing Apparatus's (SCBA) at the water production plant have been replaced with the same brand used by the Denton Fire Department. As a part of the risk management plan, all personnel at the water production plant have taken a 12-hour hazard awareness class, facilitated by the Governor's office of the State of Texas to learn about the hazards around the plant and out in the environment. In addition to the hazard awareness course, two water production maintenance employees were trained in a 40-hour hazard material tr aining course and received certification as Hazard Material Technicians. They received this training to respond to chlorine leaks at the plant as technical advisors to our primary responders, the Denton Fire Department. For incipient chlorine releases, these two employees will be the primary responders. Lake Lewisville Water Production Plant Risk Management Plan, Executive Summary Page 8 Planned changes to improve safety Before the hazard reduction/elimination study by Carollo Engineers, the water production plant had planed to retrofit the current chlorine facility with a chlorine gas scrubber system, during fiscal year 2000. A chlorine gas scrubber system pulls the air and chlorine gases from a room and neutralizes it, converting it into a brine solution. Carollo recommended building a new chlorine facility instead of a retrofit because the cost of getting the current facility up to the current building and fire codes was slightly less than the cost of a new facility. The ne w facility will be built to the current building codes and will include many safety improvements over the current facility. Some of these improvements include increasing chlorine feed capacity, enclosing all containers, a one ton capacity scrubber system, emergency shutoff valves, intruder alarms, gas detectors with alarms, and emergency backup power. The building of this facility is scheduled to begin during fiscal year 2002 and be completed in 2004. City of Denton Lake Lewisville Water Production Plant. |