Dry Creek Wastewater Treatment Plant - Executive Summary |
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Executive Summary of Risk Management Plan Dry Creek 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 Dry Creek Wastewater Treatment Plant has been in existence in its current location almost forty (40) years. The plant is currently rated to treat a maximum capacity daily design of 46 million gallons of wastewater each day. The designed peak hydraulic flow is 54 million gallons per day. It has undergone expansion three (3) times, the last of which was completed in 1995. The facility is located in the north section of Nashville and encompasses approximately 25 acres. The purpose is to treat the sewage from Madison, Goodlettsville, Hendersonville, Old Hickory and Millersville. The water received 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 360 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 one-ton cylinde rs. Usually, ten cylinders of chlorine and four cylinders of sulfur dioxide are on site. The amount of chemicals used varies with the plant flow and its characteristics. The quantity used is normally in the range a few hundred to 1000 pounds 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 2,000 pounds in ten (10) minutes. The distance to the toxic end point for each is 5.4 miles or greater. Page Two The total population that would be affected is approximately 115,564. In the alternative scenario a smaller amount of gas would be released. The scenario is that a liquid line ruptures which would release 17.8 pounds of chlorine in five (5) minutes or 16.6 pounds of sulfur dioxide in five (5) minutes. The toxic end point for each chemical would be 0.12 miles. The total population affected would be approximately 100. 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 effec ts or symptoms that could impair an individual's ability to take protective action. 4. The accident release prevention program for the Dry Creek 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 near the control room and is monitored from the control room by the Elsag, Bailey, Fischer and Porter plant control computer. 7 Electronic leak detectors are in place to provide audible and graphic alarms in the control room and on site. Chemical feed stops if a leak develops in the vacuum systems. 7 Self-contained breathing apparatus (SCBA) ar e available in the event of leaks and for personnel protection during connection/disconnection. 7 Leak repair "B" kits with both chlorine and sulfur dioxide gaskets are on site at the facility. 7 The building is marked with universal fire code hazard symbols. 5. No off site accidental releases have occurred at this plant in the last five (5) years. Page Three 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 beginning September 1999. New safety equipment is planned as new technology becomes available. These systems will be installed as current technology is surpassed. Automatic shut off valves are planned for each cylinder. |