City of Midland Water Purification Plant - Executive Summary |
|
Facility Description The City of Midland Water Purification Plant provides treated water to residential, commercial and industrial sectors of the City and surrounding areas. Raw water is processed and disinfected with ammonia and chlorine in the treatment process. The Plant maintains a maximum inventory of 24,000 pounds of chlorine in one-ton containers and a maximum inventory of 35,000 pounds of anhydrous ammonia in a bulk storage vessel. Each chemical is stored in quantities above their respective threshold level and is therefore subject to the requirements of the Risk Management Program. The Water Purification Plant has served the people of Midland since 1970. Chlorine, a chemical required by regulation to be used in the disinfection process, has been in use at the Plant since operation began. Ammonia was added to the disinfection process system in 1984. No accidental releases of chlorine or ammonia meeting the requirements of the five year accident history have occurred at t he facility. Offsite Consequence Analysis The off-site consequences of potential accidental releases of chlorine and anhydrous ammonia at the Plant were assessed in accordance with requirements established in 40 Code of Federal Regulations, Part 68. SLAB Atmospheric Dispersion Computer Model, an EPA-recognized model, was used to model a worst case release scenario and alternative release scenarios for each chemical. The worst case scenario is a model of a release under specific conditions established by EPA, including release volume, duration, and weather conditions. Active safety systems in place at the Plant that are designed to minimize the effects of a chlorine release cannot be considered in the worst case scenario. The worst case release scenario is required to assume the release in a ten minute period of the entire contents of the largest vessel of the regulated chemical onsite, which for the Plant is a one-ton chlorine container. Meteorological conditions required by EPA rules are assumed for the release. The toxic endpoint for the worst case release scenario is estimated to reach a point offsite of the facility. Since this facility is located in a populated area, the chlorine vapor would reach offsite endpoints and nearby public receptors. No sensitive environmental receptors designated by EPA are located within the release area. The alternative release scenarios represent the results more likely to occur in the event of a chlorine or anhydrous ammonia release at the Plant. Active safety systems at the Plant are considered for each alternative release scenario. Average weather conditions at the facility are used for this release scenario, as recommended by EPA regulations. For the chlorine alternative release scenario, failure of a pipe in the chlorine storage area located inside of the enclosed building is assumed. A reduction in the release distance is factored into the model to account for the release occurring inside an enclosed building . The toxic endpoint for the chlorine alternative release scenario is estimated to reach a point beyond the facility boundary, and public receptors are located within the release area. No sensitive environmental receptors designated by EPA are affected by this release scenario. For the anhydrous ammonia alternative release scenario, failure of a pipe in the ammonia feed system is assumed. The toxic endpoint for this alternative release scenario is estimated to reach a point beyond the facility boundary and public receptors are located within the release area. No sensitive environmental receptors designated by EPA are affected by this release scenario. Prevention Program The Water Purification Plant is subject to Prevention Program 2 of the Risk Management Program. In accordance with the requirements of Program 2, the Plant maintains specifications for the equipment associated with the chlorine and anhydrous ammonia feed systems and has documented the codes and standards adhere d to in designing, constructing, and operating each system. The safe operating ranges for each system are documented, and each system is operated within these safe ranges. A hazard review has been conducted for each feed system and identified action items are expected to be completed by December 31, 2000. When a major process change is made to either system, there are procedures in place to conduct a hazard review. Otherwise, a hazard review is conducted every five years. Written procedures for the operation and maintenance of both the chlorine and anhydrous ammonia systems are also in place at the Plant. Procedures are reviewed and updated periodically by facility personnel and whenever a major process change occurs. Plant operators receive training in the operation of each chemical system through classes and on-the-job instruction. Competency is determined through supervisor observation and operator demonstration of activities. Operators receive refresher training at least e very three years, or more often as necessary. Only qualified operators operate the chlorine and anhydrous ammonia systems. In accordance with the regulations, a team of facility personnel will conduct a compliance audit of the facility operations and procedures once every three years and whenever a major process modification is made. A compliance audit checklist has been developed based on American Water Works Association recommendations. A system to correct any deficiency discovered during the compliance audit is in place. In the event of an accidental release, or a situation that could lead to an accidental release, the Plant has procedures in place to investigate such incidents, develop findings and recommendations for corrective action, and implement the recommendations. Facility personnel are trained to notify emergency personnel in the event of a significant chlorine or anhydrous ammonia leak. In the unlikely event a anhydrous ammonia or chlorine release requiring the assi stance of offsite emergency response personnel occurs, the City of Midland Fire Department is responsible for responding to the accident, coordinating the emergency response effort, and notifying potentially affected areas in the surrounding community. |