CITY OF JOHNSTOWN WASTEWATER TREATMENT PLANT - Executive Summary |
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A. The city of Johnstown Wastewater Treatment Plant (WWTP) accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the EPA Prevention Program are adhered to. The City of Johnstown WWTP emergency response policy involves the the preparation of a response plan which is tailored to the facility and to emergency response services available in the community, and is in compliance with the EPA Emergency Response Program requirements. B. The City of Johnstown WWTP is a pure oxygen activated sludge sewage treatment plant that serves the city and all or part of seventeen surrounding municipalities. The type of waste treated is primarily domestic with a limited number of light industrial contributors. The final step of the sewage that is treated at the plant before it is discharged into the Conemaugh River is disinfection of the final effluent. The disinfection process is accomplished throug h the use of chlorine gas. The plant utilizes ton containers of chlorine gas for this purpose. The maximum amount of chlorine stored at the plant at any given time is fourteen one ton containers. These containers are housed in the Chlorine Room which has the Chlorine Regulator Room adjacent to it. Both of these rooms have a chlorine gas detection device that sounds an audio alarm as well as a visual alarm in the event of a leak. The facility is manned by at least two employees on each shift. The plant operates 24 hours per day, 7 days per week. A shift operator is on duty on each shift and he has, as part of his duties, responsibility to monitor all of the chlorine and its related equipment. C. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative scenario ." The "worst case release" scenario 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 scenario is defined as "more likely to occur than the worst case release scenario." D. Atmospheric dispersion modeling must be performed to determine the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint" selected by EPA of 0.0087 m/L, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). The worst case release scenario at the City of Johnstown WWTP involves a failure of a one ton container connected to the manifold that feeds the chlorine regulator. The offsite consequence analysis for this scenario was performed for the following conditions: the release of the entire amount as a gas in 10 minutes, use of the one hour average ERPG-2 as the toxic endpoint, and consideration of the population residing within a full circle with the radius corresponding to the toxic endpoint distance. EPA mandated meteoroligical conditions, namely Stability F, wind speed of 3.4 mph, highest daily maximum teperature (116 degrees F), and average humidity (65%), were used for the analysis. When atmospheric dispersion modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 3.0 miles and and an estimate of residential population potentially affected of 3,500 was obtained. The alternative release scenario involves the rupture of a flexible connection to a one ton container, possibly due to physical contact by an employee. The relea se is estimated to be 571 pounds over one hour at an average rate of 9.52 pounds per minute. Toxic endpoint distances to the ERPG-2 level was obtained. The typical meteorological conditions used were Stability D, wind speed 6.7 mph, 77degrees F, and 63% average humidity. The estimated distance traveled to the toxic endpoint is 0.2 miles. Actuation of the chlorine alarm is an active mitigation measure considered. An additional mitigation system is the use of vacuum withdrawal from the ton containers. This will reduce significantly the amount of chlorine released in a pigtail rupture. E. The general Johnstown WWTP accidental release prevention program is based upon the following elements: 1. Operator training 2. Preventive maintenance program 3. Safety equipment usage 4. Use of accurate and effective operating procedures 5. Performance o f a hazard review of equipment and procedures 6. Implementation of an auditing and inspection program. Chemical specific prevention steps include availability of self-contained breathing apparatus (SCBA), the presence of chlorine gas detection equipment, and the on-site chlorine ton container repair kit. Further, each Monday each shift has a safety meeting to discuss the possible hazards in the workplace. The result of these meetings is a report that is forwarded to the chief operator that outlines any safety concerns of the employees. This report can contain information specific to any deficiencies in the chlorination supply and equipment as weel as other areas of the plant. F. One minor accidental release of chlorine occurred at the plant in the last five years. It was a release of less than 10 pounds so was not a reportable release as per the LEPC standards. The release was a leak of the packing on a valve of a ton container and was outfitted with a repair kit. The container was r eturned to thte supplier for further action. G. The facility has emergency response program which has been formulated by the LEPC and is reviewed and updated annually. The program includes an emergency response decision tree and a notification, evacuation, and detour plan. H. Several changes to improve safety were recommended by the EPA in 1998. These changes were implemented in 1998 and 1999. |