Central Wastewater Treatment Plant - Executive Summary

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Executive Summary of Risk Management Plan 
Central Wastewater Treatment Plant 
 
 
 
1.  The city of Nashville's Department of Water and Sewerage Services (Metro Water Services) Risk Management Plan is a combination of technology, procedures, training and management.  Each element of the U.S. Environmental Protection Agency  Risk Management program is addressed.  The approach is to prepare a plan tailored for each facility to increase knowledge, prevent accidents, and to respond to emergencies. 
 
2.  The Central Wastewater Treatment Plant has been in existence in its current location almost fifty (50) years.  The plant is currently rated to treat a maximum capacity of 330 million gallons of wastewater each day.  It is now under expansion and several major expansions have been completed.  The facility is located in the downtown section of Nashville and encompasses approximately 160 acres.  The purpose is to treat the sewage from the south, central, and east sections of the city.  The water re 
ceived at the plant as sewage is treated to remove the contaminants by a multi-step process known as activated sludge treatment.  The material removed from the water is called sludge or biosolids.  Each month the plant disposes of approximately 2,800 dry tons of biosolids.   The clean, clear water is then returned to the Cumberland River.  The final phase of treatment is chlorination, to disinfect the water and dechlorination to reduce the impact of the chlorine on the Cumberland.  The chlorine facility includes piping, valves, pressure gauges, evaporators, and chlorinators for chlorine.  It also has piping, valves, pressure gauges, evaporators, and  sulfinators for the declorination agent (sulfur dioxide).  Both chlorine and sulfur dioxide are hazardous because they are respiratory irritants when inhaled.  Liquid chlorine and sulfur dioxide are stored and used from ninety (90) ton rail cars.  Usually, two rail cars of each chemical are on site.  The amount of chemicals used varies wit 
h the plant flow and its characteristics.  The quantity used is normally in the range of 1 to 3 tons of each per day.  The chlorine facility is normally unmanned, however; it is monitored remotely from the plant control room.  The plant is manned 24 hours a day, seven days a week and the operators visit the chlorine site at various times during the day.  Various types of safety equipment, alarms, sensors, and monitors are in place at this facility.      
 
3.  Off site consequence analysis has been completed for each chemical.  Both the worse case and alternative release scenarios have been calculated using three different methods.  Manual calculations, TVA air models, and RMP comp were all used and each method obtained virtually the same results. The calculations used here are from TVA.  In the worst case scenario, by EPA rule, the total amount released for chlorine and sulfur dioxide is 180,000 pounds in ten (10) minutes.  The distance to the toxic end point for each is 25 miles or gre 
ater.  The total population that would be affected is approximately 962,161.  In the alternative scenario a smaller amount of gas would be released.  The scenario is that a liquid line ruptures which would release 3,918 pounds of chlorine in  
 
sixty (60) minutes or 3,648 pounds of sulfur dioxide in sixty (60) minutes.  The toxic end point for each chemical would be .81 miles.  The total population affected would be approximately 25,000. It should be noted that 40 CFR 68 specifies the toxic end point for chlorine is .0087 mg/L and .0078 mg/L for sulfur dioxide. These were developed by the  American Industrial Hygiene Association, and are defined as the maximum airborne concentration below which it is believed nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action. 
 
4.   The accident release prevention program for the Central  
Wastewater Treatment Plant includes the following: 
 
7 Extensive operator training. 
7 Preventive Maintenance Program for the chlorine equipment. 
7 Use of state of the art process and safety equipment. 
7 Use of specific operating procedures written and reviewed by plant personnel. 
7 Scheduled performance reviews for hazards in the procedures and equipment. 
7 Implementation of a compliance inspection program. 
 
Presently, specific accident prevention measures include the following: 
 
7 The site is monitored from the control room by two closed circuit cameras. 
7 Electronic leak detectors are in place which provide automatic shut off of the chemicals and audible and graphic alarms in the control room and on site. 
7 Breathing air tanks and self contained breathing apparatus (SCBA) are available in the event of leaks and for personnel protection during connection/disconnection. 
7 Leak repair "C" kits with both chlorine and sulfur dioxide gaskets are on site at the facility.  
7 The building i 
s marked with universal fire code hazard symbols. 
 
5.  No off site accidental releases have occurred at this plant in the last five (5) years. 
 
6.  The plant has an emergency response plan and the Nashville Fire Department is aware  
of the possible hazards.  Metro Water Services and the Nashville Fire Department are members of the Local Emergency Response Planning Committee (LEPC).  The program includes a response decision flow chart and a notification plan.  Plant personnel respond to and repair minor leaks and the Fire Department is called in the event of a significant accident. 
 
7.  Future plans include a more extensive training program for the plant staff.  New safety equipment is planned as new technology becomes available.  These systems will be installed as current technology is surpassed. 
 
8. Training will begin September 1999.
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