Reynolds R. Ridgely Wastewater Plant - Executive Summary

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The Reynolds R. Ridgely Wastewater Treatment Plant has been successfully serving the community of Columbus, Mississippi for almost two decades.  Located in the southeast corner of Columbus on West Yorkville Road, the plant lies directly east of the Luxapallila Creek.  On average the plant treats 7.5 million gallons per day of sanitary sewage and has the capacity to treat over 10 million gallons per day.  The Plant boasts of a flawless safety record with no accidents to report over the history of the facility.  This flawless safety record can be attributed to the awareness and conscientiousness of the administration and staff. 
To further improve the overall safety of the plant, a Risk Management Plan has been developed for the hazardous chemicals used in the treatment process.  When dealing with hazardous chemicals, it is imperative to take all necessary precautions to protect the safety of the employees and the surrounding community.  The Wastewater Plant has accomplished this throu 
gh constant employee safety training, the use of proper methods and equipment for handling the chemicals, and the preparation of emergency response procedures. 
This Risk Management Plan has been prepared for chlorine and sulfur dioxide, two essential chemicals in the treatment of municipal sanitary sewage.  Chlorine is a strong disinfectant and is used in the treatment process to eliminate pathogenic organisms in the final effluent.  Sulfur dioxide is added to the final effluent to remove the residual chlorine before it is discharged from the plant.  Both chemicals are stored on-site in the chlorination/dechlorination building near the center of the facility.  A maximum inventory of 24,000 pounds of chlorine and 12,000 pounds of sulfur dioxide can be found at the plant at one time.  The chlorination/dechlorination building serves to supply, meter, and apply each of the chemicals to the final effluent.   
Both chlorine and sulfur dioxide are listed by the EPA as extremely hazardous sub 
stances (EHS.)  Chlorine has a characteristic penetrating odor and is greenish yellow in the gas phase and clear amber under pressure in the liquid phase.  Chlorine gas is primarily a respiratory irritant, while liquid chlorine will cause burning to the eyes and skin.  Sulfur dioxide can be recognized by its strong characteristic odor and will also cause damage to the respiratory system and burning of the eyes and skin due to the freezing effect of the liquid.  Yet, with the proper equipment and proper handling of these chemicals, the hazards can be controlled. 
As part of the Risk Management Plan, both a worst case and an alternative case  release scenarios were examined and the off-site impacts were analyzed.  Scenarios established and recommended in the EPA's Risk Management Program Guidance for Wastewater Treatment Plants-Off-Site Consequence Analysis were used for the analysis.  The worst case release scenario assumes the release of 2,000 pounds of liquid chlorine over a 10 minute 
interval.  The distance to the toxic endpoint, or the affected area, for this type of release is 1.3 miles from the spill.  Facilities that would be impacted off-site within this radius include residences (approximately 10,000 people), schools, the County Jail, recreational areas, and various industrial and commercial areas.  An identical worst case release scenario was analyzed for sulfur dioxide.   
These scenarios, although possible, are very unlikely to occur at Columbus's Wastewater Plant due to the physical layout of the facility.  This model assumes that the spill takes place outside in a relatively flat terrain.  Yet, all cylinders at the facility are stored inside the chlorination building, which would serve as an enclosure for the gas.  The only time the cylinders are outside is during unloading from the vehicles upon delivery to the plant.  The EPA suggests using a factor of 0.55 to determine the actual release rate if the chemicals are inside a building, but the original r 
elease rate was chosen to cover the minor amount of time the cylinders are being unloaded outside.  Also, the Wastewater Plant is surrounded by a levee to protect from flooding, placing the chlorination building in a depression.  Both chlorine and sulfur dioxide are denser than air and, therefore, will sink to the lowest elevation. In the event of a spill these gases would most likely be confined to the plant grounds by the levee.            
The alternative release scenarios chosen for chlorine and sulfur dioxide are much more probable assumptions in the unlikely event of a spill.  The chlorine scenario assumes a ton cylinder is dropped during unloading at the facility, creating a 0.25 inch hole in the bottom of the cylinder through which liquid chlorine escapes.  This release allows 2,000 pounds of chlorine to spill at a rate of 150 pounds/minute.  The affected radius for this type of spill is 0.20 miles, which would cause minimal off-site impact.  No facilities of any type or recrea 
tional areas lie within 0.20 miles of the Wastewater Plant, therefore, no population would be put in danger.  The sulfur dioxide scenario assumes a relief device fails, allowing liquid sulfur dioxide to escape through a 0.25 inch opening.  This release allows 2,000 pounds of sulfur dioxide to spill at a rate of 99 pounds/minute.  The affected radius of impact is likewise 0.2 miles for this scenario.  As with the worst case scenarios, both the chlorine and sulfur dioxide would most likely be confined to the plant grounds by the levee.  Also, the relief valve failure on the sulfur dioxide cylinder would most likely take place indoors and, therefore, be enclosed.    
Another part of the Risk Management Plan is the prevention program.  This program covers safety information, a review of potential hazards, operating procedures, employee training, and maintenance of equipment.  It is essential to have up-to-date and complete information available on these topics to protect the employees and  
the surrounding community by eliminating possible hazardous situations.  The Wastewater Plant keeps current material safety data sheets on chlorine and sulfur dioxide available to the staff at all times.  There are also equipment specifications and the appropriate codes and standards used to operate the process available in the office building.   
A hazard review of the chlorination and sulfonation process was conducted on May 17, 1999.  The purpose of the hazard review is to identify all hazards associated with the chemicals and processes, opportunities for equipment malfunction or human error, safeguards in place, and detection or monitoring equipment in place or needed.  Possible hazards identified include toxic releases, overpressurization of a cylinder, and equipment failure.  Safeguards in place to protect against these hazards include vent lines, manual and automatic shutoff valves, fire resistant walls, and the fact that the cylinders are stored inside a building that is surrou 
nded by a levee.  Emergency air supply is also available for employees in the case of a release.  Leak detectors are provided in each of the process rooms and will trigger audible and visible alarms at the chlorination building.  Since the hazard review was conducted, remote alarms have also been set up to sound in the main office building at the plant.   
Operating procedures are available to all employees in the Operation and Maintenance Manuals, which are located in the main office building.  These procedures cover normal and emergency operations of all the equipment and include specific steps to be carried out in the case of a release.  All operators working in the plant have been properly trained on the plant operations and emergency procedures.  Classroom and on-the-job training is conducted several times throughout the year to refresh employees.  There are also plant operators certified to use self-contained breathing apparatuses (SCBA's.)  Routine maintenance of the equipment i 
s conducted by trained operators.  An outside contractor is brought in annually to service the chlorination and sulfonation equipment. 
Due to the safety procedures discussed above and the adherence to these procedures by the plant operators, the Wastewater Plant has never had an accidental release.  Although it is unlikely that the plant will have an accidental release in the future, emergency response plans are in place in the event one does occur.  The Wastewater Plant has coordinated with the Lowndes County Local Emergency Planning Committee (LEPC) to be included in the community emergency response plan.  By being included in this plan, the LEPC will respond to a potential release at the facility.  In addition to this, the plant has also set-up written procedures and emergency check lists to be carried out by employees in the case of a release.  These procedures outline safe handling procedures for the leaking containers and require immediate notification to the emergency response  
agency.  This emergency response plan will help the Reynolds R. Ridgely Wastewater Treatment Plant carry on its tradition of maintaining a flawless safety record.
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