Ozark Water Treatment Plant - Executive Summary

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Policy Statement 
It is the Little Rock Municipal Water Works' (LRMWW) policy to operate Ozark Water Treatment Plant (WTP) safely, reducing to the greatest extent possible any hazards associated with the chlorine system and reducing any subsequent risk to the surrounding community, personnel, and environment.  Safe operation depends on proper storage of chlorine, proper handling of the chlorination system, and inherent safety features in the design of the chlorination system.  Safety in storage and handling is achieved through the use of safe handling procedures and training of personnel.   
The policy includes working with the surrounding community and local emergency response agencies to promote a spirit of cooperation and teamwork, to orchestrate an effective contingency plan in the unlikely event of a process incident occurring at the Ozark WTP.  The emergency response plan includes procedures for notifying the Little Rock Fire Department.  
Stationary Sources and Regulated Substance 
Primary Activities:  The primary activity is municipal water treatment.  The Ozark WTP originally was constructed in 1936 and has a current capacity of 24 million gallons per day (mgd).  The sludge from the facility is pumped to the Fourche Creek Wastewater Treatment Plant (WWTP) as a solution. 
Use of Regulated Substances:  Chlorine is used primarily as a disinfectant.  Other possible uses of chlorine are for iron removal. 
Substance Handled or Stored:  Chlorine:   
Total Amount Stored:  16 one-ton containers, equivalent to 36,800 pounds. 
Worst-case Release Scenario 
Failure of one liquid chlorine container resulting in a release of 2,300 pounds of chlorine gas in 10 minutes.  Passive mitigation is not considered because the containers are stored in the open.  The release rate of 1.74 kg/s is modeled using DEGADIS 2.1. 
Distance to Endpoint:  Under the-worst case weather conditions prescribed by the RMP Rule, the distance to a toxic endpoint of 0.0078 mg/L (or 3 ppm) is 1.98 mil 
es, beyond which there will be enough dispersion that a hazard to the public will no longer exist. 
Population Exposed:  It is estimated based on the USCB population density for the City of Little Rock that 21,000 persons would be affected within the WRS toxic endpoint circle. 
Environmental Receptors:  The Little Rock State Capitol building is within the WRS toxic endpoint circle. 
Alternative Release Scenario 
Release of chlorine from a <-inch-diameter pipe connecting the chlorine container to the feed manifold.  For a release duration of 20 minutes, the calculated release rate is 0.018 kg/s.  The release rate calculation is based on the chlorine density of 2.899 kilograms per cubic meters (kg/m3) at 298: Kelvin (K), container pressure of 7.93 atm, the ratio of chlorine heat capacities of 1.355, and a passive mitigation of 45 percent because of the enclosed scale room.  The release rate of 0.018 kg/s is modeled using DEGADIS 2.1. 
Distance to Endpoint:  Under realistic weather conditions 
of 3.0 meters per second (m/s) wind speed and a wind stability class of "D," chlorine would travel 0.17 mile or 0.27  kilometer (km) before dispersing enough to no longer pose a hazard to the public.  The toxic endpoint of 3 ppm was used for the ARS. 
Population Exposed:  It is estimated, based on the USCB population density for the City of Little Rock, that 150 persons would be affected within the ARS toxic endpoint circle. 
Environmental Receptors:  There are no environmental receptors within the ARS toxic endpoint circle. 
Accidental Release Prevention Program and Chemical-specific Prevention Steps 
The LRMWW's Ozark WTP is in compliance with the RMP Rule, 40 CFR 68.  The facility has conducted a comprehensive review of all systems, as well as of administrative, technical, and operating and maintenance procedures, in addition to the other required program elements of the RMP Rule.  A hazard review was conducted at this facility using a "What If" analysis. 
Five-year Accident History 

he LRMWW's Ozark WTP has never had a release of chlorine resulting in offsite injury or dispersion, or in onsite injury. 
Emergency Response Program 
The LRMWW's Ozark WTP has an Emergency Response Program, which coordinates response efforts with the Little Rock Fire Department's HAZMAT team, the police department, and the hospital.  Response activities also have been discussed with the Arkansas Office of Emergency Services. 
Planned Changes to Improve Safety 
It was observed during the hazard review that the LRMWW's Ozark WTP has the necessary equipment and operating and training procedures required for the safe operation of the chlorination system.  The following recommendations for improving the safety of the chlorination process were made: 
1. Reduce the set point for the chlorine detection and alarm system to 3 ppm. 
2. Install a wind sock to indicate the wind direction during emergencies.  
3. Provide a copy of the updated emergency response procedures for chlorine to the Little Rock  
Fire Department.
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