Authority of the Borough of Charleroi - Executive Summary |
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EXECUTIVE SUMMARY 1. Purpose Chlorine is used as a disinfectant in the wastewater treatment. The raw wastewater contains microorganisms that are harmful to human health. Several treatment processes are utilized at the plant to treat the raw wastewater and a chlorination system provides disinfection of the final effluent prior to discharge. 2. Storage Chlorine is delivered to the treatment plant in one-ton containers. A maximum of 4 one-ton containers of liquid chlorine are stored on site in the chlorine storage room. 3. Overview of the Wastewater Treatment Plant The Authority of the Borough of Charleroi (ABC) Sewage Treatment Plant treats approximately 1.5 million gallons per day (MGD) of raw domestic wastewater at the treatment plant. The chlorine used for disinfection is supplied from one-ton containers. A maximum of four one-ton containers of liquid chlorine are stored on site. This is the only chemical substance at this facility that is regulated under U. S. EPA's Ac cidental Release Prevention Program. Chlorine gas is primarily a respiratory irritant. In sufficient concentrations, the gas irritates the mucous membranes, the respiratory tract and the eyes. In extreme cases difficulty in breathing may increase to the point where death can occur from respiratory collapse or lung failure. The characteristic, penetrating odor of chlorine gas usually gives warning of its presence in the air. At high concentrations, it is visible as a greenish yellow gas. Liquid chlorine in contact with the skin or eyes will cause chemical burns and/or frostbite. Chlorine containers are thoroughly inspected for mechanical integrity and leaking valves prior to leaving the supplier's premises. The containers are off-loaded from the delivery truck at the treatment plant by an overhead crane with a lifting beam that is specially designed for ton-containers. The off-loaded containers are also inspected by ABC personnel. There are two identical systems that can deli ver chlorine gas, at the correct flow rate, to the wastewater. One system is normally active and the other system is on standby. Although both systems can be used simultaneously, one system has more than adequate capacity to supply the required amount of chlorine to the treated wastewater. The liquid chlorine leaves the ton container as a gas. There are two containers connected to a common pipe (manifold), however, only the chlorine gas valve on one container is normally open. This container is used until empty and then an automatic switchover puts the other container in service. There are two chlorinators that are connected to the manifold and they regulate the flow of chlorine gas to the wastewater. The capacity of one chlorinator is more than adequate to supply the required amount of chlorine to the wastewater. The chlorine gas flows from the container to the manifold and then to the chlorinator. The chlorine gas is drawn from the chlorinator by inducing a vacuum in the line. Vacuum regulators are located on the ton-containers in order to induce the vacuum from the containers to the chlorinators. In addition, the flow of wastewater through an eductor creates a vacuum in the line from the chlorinator to the eductor and also mixes the chlorine gas with the wastewater. If the water supply to the eductor is stopped, or the operating vacuum is lost for any other reason, the spring-loaded gas inlet valve immediately closes to isolate the chlorinator from the chlorine gas supply. In addition, the vacuum regulators located on the ton-containers will prevent a chlorine release if the flow of chlorine between the ton-container and the chlorinator is interrupted. The average chlorine usage is 40 pounds per day. 4. Accidental Release Prevention Accidental releases of chlorine are prevented by routine training and adhering to the written operating procedures that cover the chlorination system from the ton-container unloading through the mixing of the chlor ine gas with the water. These procedures cover normal operations and emergency operations where personnel may have to respond to an accidental release of chlorine. The chlorine system is inspected at least once per shift and leak testing is performed on the valves and fittings when ton-containers are changed-out and at other times if a leak is suspected. Employees that are responsible for disconnecting empty containers and connecting filled containers to the chlorination system have been trained on the operating procedures, inspection of valves, fittings, and the connected piping, and leak testing with an aqueous ammonia solution. Aqueous ammonia reacts with chlorine gas to form a very visible white cloud. An outside contractor inspects the chlorination system and performs preventive maintenance on this system twice a year. This insures that worn or damaged parts are replaced and routine maintenance is performed on the chlorinators and other equipment. These preventive measures h ave resulted in the absence of any accidental release of chlorine that resulted in personal injury or property damage since the treatment plant began operation. The treatment plant maintains one Self-Contained Breathing Apparatus (SCBA) and The Chlorine Institute's Emergency Kit "B" for ton containers. This equipment is stored in a room that is adjacent to the room that houses the ton containers. ABC personnel receive annual training on the use of the breathing apparatus and the emergency kit. In addition, ABC personnel plan to implement procedures that require employees to wear the SCBA equipment while disconnecting and changing the ton-containers. Kit "B" contains the necessary tools and other equipment to contain valve leaks and repair small holes in a ton container, and capping devices for the fusible plugs in each end of the container. Ton containers are equipped with six fusible metal plugs, three in each end. The fusible metal is designed to melt between 158 and 165 degre es F to relieve pressure and prevent rupture of the container in case of fire or other exposure to high temperature. Chlorine gas is heavier than air and will settle to the lowest elevation when released. The chlorine storage area is equipped with an exhaust fan that is mounted near the floor on an outside wall. There are also air intake vents located near the floor so that the chlorine gas will be vented outside the building. The fan is automatically activated when the door to the chlorine storage room is opened. Two exit doors are provided in the chlorine storage room. 5. Emergency Response Plan The ABC has developed an Off-Site Response Plan in the event of an accidental release of chlorine at the wastewater treatment plant. This Off-Site Response Plan has been submitted to the Local Emergency Planning Committee of Washington County and the Pennsylvania Emergency Response Commission for review and approval. Once approved, the ABC Off-Site Response Plan will be included in the written community emergency response plan. This plan was developed in accordance with the provisions set forth in Title III of the Superfund Amendments and Reauthorization Act of 1986. The plan assigns release response procedures to the emergency coordinator at the ABC, Washington County Emergency Control, Charleroi Volunteer Fire Department, Local Police, Emergency Medical Services, and the Washington County Emergency Management Coordinator. The plan is updated as necessary, including the list of emergency telephone numbers. The Charleroi Volunteer Fire Department has visited the treatment plant on several occasions and has trained ABC personnel on the proper use of the SCBA equipment. If a chlorine leak develops in a ton-container or in the connected piping, valves, or other equipment, a chlorine monitor in the chlorine storage area will activate an audible alarm in this area. If a chlorine release should occur during off-hours, the chlorine alarm is tied in to the secu rity system at the plant for 24-hour notification of a release. The treatment plant emergency operating procedures will be followed to determine the severity of the chlorine release and whether or not the gas may migrate offsite. If the chlorine release may travel offsite, then the Offsite-Response Plan will be activated. If the chlorine release does not pose a threat to the general public, ABC personnel will repair the leak. ABC personnel have installed a windsock near the chlorine storage building so that the area that is likely to be affected by a chlorine release can be determined. 6. Worst-Case and Alternate-Case Accidental Release Scenarios Worst-Case Release Scenario The worst-case release scenario as postulated in the regulation (40 CFR 68.25) is the release of the greatest quantity (of chlorine) in a single vessel. The entire contents of this vessel are assumed to be released as a gas over a 10-minute period. The largest single vessel at the treatment plant is a one-ton container; therefore, 2,000 pounds of liquid chlorine will be released as a gas over a 10-minute period. A release of this magnitude would only be possible if the shell of the container failed and the liquid chlorine formed a pool and vaporized over a 10-minute period. The likelihood of this type of catastrophic release is very minimal. The off site consequence of this release was determined by use of U. S. EPA's RMP*Comp software. The RMP*Comp results indicate that the chlorine concentration will exceed 3 parts per million (ppm) out to a radial distance of 1.3 miles from the chlorine storage room. This is the distance to the toxic endpoint. Beyond 1.3 miles the chlorine concentration will be less than 3 ppm. Short-term exposure to chlorine concentrations less than 3 ppm is not considered to be a health hazard. The chlorine storage room is located on a hillside that slopes downward to the west and south. Based on the guidance provided in the regulation and U. S. EPA's Ri sk Management Program Guidance for Wastewater Treatment Plants, the area surrounding the treatment plant was classified as urban due to the presence of nearby buildings and other structures, trees, and hilly terrain. The meteorological conditions associated with the worst-case release scenario, as prescribed in the regulation, is a wind speed of 1.5 meters per second (3.36 miles per hour) and very stable atmospheric conditions. These stable atmospheric conditions will limit the mixing of the chlorine gas with the ambient air as the gas travels downwind from the point of release. The cloud formed by the chlorine release will grow in size and decrease in concentration as it travels downwind. Alternate-Release Scenario The alternate release scenario is one that is more likely to occur than the worst case release scenario. For this scenario, it was assumed that a leak from the ton container occurs and mitigation occurs in one hour. This assumption is based on the alternate release s cenarios listed in Edition 3 of The Chlorine Institute Pamphlet No. 74 - Estimating the Area Affected by a Chlorine Release, April 1998. Less than half of the contents of the ton-container (762 pounds) is released over a one-hour period. For this scenario, the meteorological conditions prescribed in the regulation are neutral atmospheric stability conditions and a wind speed of 3 meters per second (6.7 miles per hour). RMP*Comp was also used to determine the radial distance at which the chlorine concentration falls off to less than 3 ppm. This distance to the toxic endpoint, as determined by RMP*Comp, is 0.10 miles (528 feet). There are no schools or hospitals within this radial distance, however the population within this radius is approximately 15. It is unlikely that the entire contents of a ton-container would be released prior to ABC personnel closing the shutoff valve on the ton container. Actual response time to shut off the valve is estimated to be 15 minutes. The wor st-case and alternate release scenarios are summarized in Table 1 along with some additional information regarding population estimates, schools, hospitals and other building or recreation areas within the radial distance to the toxic endpoint. Census data and the location of schools, hospitals, etc. were obtained from the LandView III mapping system that includes database extracts from U. S. EPA, the Bureau of Census, the U. S. Geological Survey, the Nuclear Regulatory Commission, the Department of Transportation, and the Federal Emergency Management Agency and were confirmed by ABC personnel. 7. Planned Changes to Increase Safety 7 Increase the frequency of practice drills to respond to an accidental release of chlorine to three times per year. 7 Implement the use of SCBA equipment while disconnecting and changing ton containers. 7 Encourage the local volunteer fire companies to become more familiar with the chlorine system at the treatment plant. Table 1 Summary of the Wors t-Case and Alternate Release Scenarios Worst-Case Release Alternate Release Type of Accidental Release Rupture of ton-container Gas valve leak Quantity of Chlorine Released 2,000 pounds 762 pounds Duration of Chlorine Release 10 minutes 60 minutes Rate of Release of Chlorine Gas 200 pounds per minute 12.7 pounds per minute Wind Speed 1.0 meters/second (3.36 mph) 3.0 meters/second (6.7 mph) Atmospheric Stability Class F (very stable) D (neutral) Method used to determine toxic endpoint RMP*Comp RMP*Comp Chlorine concentration at the endpoint 3 parts per million (ppm) 3 parts per million (ppm) Radial distance to the toxic endpoint 1.3 miles (6,900 feet) 0.1 miles (528 feet) Estimated population within radial distance 3,450 15 Number of residences 1,450 7 Number of hospitals 0 0 Number of schools 3 0 |