Omohundro Water Treatment Plant - Executive Summary

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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 US 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 Omohundro Water Treatment Plant has been in existence in its current location for 111 years.  The Plant is currently rated to treat a maximum capacity of 71.3 million gallons of water each day.  It is now under expansion to increase capacity to 90 million gallons per day.  The facility is located East of downtown Nashville and is situated on approximately 11acres.  Along with the K.R. Harrington Plant, Omohundro produces potable drinking water for the service area.  The Plant utilizes the co 
nventional treatment process to produce potable drinking water.  Chlorine is utilized in this process train to disinfect the water.  The chlorine feed system includes piping, valves, pressure gauges, evaporators, and chlorinators.  Chlorine is hazardous because it is a respiratory irritant when inhaled.  Liquid chlorine is stored in one ninety- ton rail car, ten (10) one ton cylinders, and eight (8) one hundred and fifty-pound cylinders.  The amount of chemical used averages around one half ton per day depending on raw water conditions and flow.  The chlorine tank car is monitored continuously by closed circuit television and chlorine detectors with audible alarm systems.  Plant operators also inspect the tank three times a day.  This car is located in a secure fenced area and protected by security on evenings, nights and weekends. Operating procedures require only one one-ton cylinder is in service at any time.  The one hundred and fifty-pound cylinders are stored in a dedicated room. 
3. Off site consequence analysis has been completed for chlorine gas.  Both the worst case and the second worst-case scenarios have been calculated using three different methods.  Manual calculations, TVA air models, and RMP Comp were all used and each method achieved virtually the same results.  The calculations used here are from TVA.  In the worst case scenario, 180,000 pounds of chlorine, liquefied by pressure at 120 psi, would be released by the total destruction of a railcar.  The distance to the toxic endpoint is greater than twenty-five (25) miles.  The total population that would be affected within 25 miles is approximately 992,969 persons.  In the second worst-case scenario, approximately 2000 pounds at 120 psi released by the total destruction of the ton-cylinder would have an estimated end point of 5.4 miles.  The total population affected in this scenario would be 225,802. 
     In the first of two alternative scenarios, a one-inch diameter line is sheared at the chlor 
ine railcar and leaks 157 pounds per minute for duration of 5 minutes.  The endpoint would be 1.2 miles.  The population affected would be 12,699 persons.  The second alternative is a leak on a 0.25-inch line on a ton cylinder, leaking 5.59 pounds per minute for 5 minutes.  The endpoint would be 0.12 miles. 
4.    The accident release prevention program for Omohundro WTP includes extensive operator training, a Preventative Maintenance program for chlorine equipment, state of the art process and safety equipment, written operating procedures, scheduled performance reviews for procedures and equipment, and implementation of a compliance inspection program. 
5.  No off site accidental releases have occurred at this plant in the previous five 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).  Th 
e program includes a response decision flow chart and a notification plan.  Plant personnel respond to and repair minor leaks and the Fire Department are called in the event of a significant accident. 
7. Future plans include a more extensive training program for the plant staff.  Training is now scheduled to begin September, 1999. New safety equipment planned will include additional chlorine alarms and an automatic shut off system for the one ton chlorine cylinders and railcar.
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