City of Ravenna Water Treatment Plant - Executive Summary |
|
A. The City of Ravenna Water Treatment Plant (RWTP) Accidental Release Prevention Policy involves a unified approach that integrates technology, procedures and management practices. All applicable procedures of the U.S. Environmental Protection Agency (USEPA) Prevention Program are adhered to. The Ravenna Water Treatment Plant Emergency Responce Policy involves the perperation of reponce plans which are tailored to the Ravenna Water Treatment Plant Facility and to the emergency response services available in the community, and is in compliance with the USEPA Emergency Program requirements. B. The Ravenna Water Treatment Plant was built and put on line in June 1984 to supply water to the City of Ravenna residences and the Rootstown Water Service Company to the south. This water currently serves the entire City of Ravenna, parts of Ravenna Township and approximately one third of the supply to Rootstown Water Service Company. An emergency water transmission main to the City of Kent to th e west is currently being worked on. The water plant is located at 5383 Lakewood Road next to Lake Hodgson Recreational facility and Reservoir. The Plant includes a chlorination room, which contain liquid chlorine cylinders, a chlorinator and varoius safety devices. The amount of chlorine handled is four one ton containers. The chlorinator and equipment room is normally unmanned and can only be entered from a separate outside entrance apart from the main building. Water Treatment Operators visit the facility or room daily per shift and respond to any trouble alarms which may occur. C. The offsite consequence analysis includeds consideration of two chlorine release scenarios, identified as "worst case release" and "alternate scenerio". The first scenerio 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 scenerio is defined as "mor e likely to occur than the worst-case scenerio". Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine released before its concentration decreases to the "toxic end point" selected by EPA of 3 ppm, which is the Emergency Response Planning Guidline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiecing of developing irreversable or other serious health effects or symptoms which could impair an individual's ability to take corrective action". The residential population within a circle with a radius corresponding to the toxic end point distance has to be defined "to estimate the population potentially affected". The worst case senario at the Ravenna Water Treatment Plant involves a failure of four ton containers which could connected concurrectly (a total of 8 ,000 lb. of chlorine). The offsite consequence analysis for this senario was performed for two sets of conditions. The first set followed conditions predefined by EPA, namely the release of the entire amount as a gas in 10 minutes, use of the one hour average ERPG-2 as the toxic end point, and consideration of the population residing within a full circle with a radius corresponding to the toxic end point distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis, however, the assumption used may be unrealistic because: 1. Only a fraction (about 26% of the total) of the compressed liquified chlorine released to the atmosphere flashes as a vapor. The remaining unflashed liquid forms a liquid-droplet aerosols. This results in the formation of a very dense chlorine cloud consisting of vapor and liquid droplets, with dispersion characteistics significantly different than a cloud consisting only of chlorine gas. 2. It is not appropriate to compare a 10-minute release to a one hour average standard. The 3ppm one-hour ERPG can be modified using available time of exposure/concentration relationships to match the ten minute release time; the value obtained is 7.3 ppm. 3. Only the population within an elliptical plume extending downwind of the release point is potentiallly affected. This plume area, or footprint, is approximately 11% (one tenth) of the area of the full circle. EPA-mandated meteorlogical conditions, namely stability F, wind speed of 1.5 m/sec, and average humidity of 63% were used for both sets. When atmospheric dispersion modeling for the worst case senario was performed using EPA assumptions, a distance to toxic end point of 1.9 miles and an estimate of residential population affected of 4,000 was obtained. When the same modeling was performed with the second set of conditrions, namely using a vapor/aerosol release, a 10-minute average ERPG-2 of 7 ppm, and consideration of a plume footprint only, a distance to toxic end point of 0.1 and an estimate of population potentially affected of 20 resulted. The alternative release senario involves the rupture of the flexible connections (pigtails) connected to two ton containers, possibly due to an additional mitigation system installed in the conversion of the existing chlorine to a remote vacuum type, with pressurized chlorine gas piping replaced with vacuum piping. This will reduce significantly the amount of chlorine released in case of a pigtail rupture. D. The General Ravenna Water Treatment Plant accidental release prevention program is based on the following key elements: - High level of training of the operators - Preventative maintenance program - Use of state-of-the-art process and safety equipment - Use of accurate and effective operating procedures written with the participation of the operators - Performance of a hazard review of equipment and procedures - Implementation of an auditing and inspection program Chemical-specific prevention st eps include availability of self-contained breathing apparatus (SCBA) worn by the operators during connection/disconnection of chlorine supply, awareness of hazardous and toxic properties of chlorine, and the presence of chlorine detectors. E. No accidential releases of chlorine have occured at this facility (RWTP) in the past 5 years. F. The RWTP has an emergency responce program, which has been coordinated (reviewed) by the City of Ravenna Fire Department, which is a member of the local Emergency Responce Planning Committee (LEPC). This program includes an emergency response decision tree and notification program. Emergency response drills and drill evacuations are conducted every 12 months; energency operating and response procedures are also reviewed at this time. G. Three (3) changes to improve safety (recommended actions) were identified in April, 1999. These recommended actions have now been evaluated and implimented as required. |