Tawakoni Balancing Reservoir - Executive Summary

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INTRODUCTION 
 
The Accidental Release Prevention Risk Management Program rule (40 CFR Part 68) is similar to the Occupational Safety and Health Administration's Process Safety Management Program, which is designed to protect workers from accidental releases of hazardous substances.  The Risk Management Program rule addresses over 100 chemical substances-77 of which are acutely toxic and 63 of which are flammable gases-and the accidental release of these substances. The United States Environmental Protection Agency (USEPA) estimates that over 100,000 sources are covered by the rule, including chemical manufacturers and wholesalers, certain retailers, potable water treatment systems, wastewater treatment plants, ammonia refrigeration systems, and federal facilities. 
 
The TBR falls under this regulation because of the on-site storage of chlorine.  The amount of chlorine stored is well above the threshold limit specified by the USEPA thereby making the facility subject to compliance with th 
e regulation.  The TBR personnel have complied with the USEPA Risk Management Program rule and have completed an Accidental Release Prevention Program (ARPP) Plan that contains the following required information: 
 
7 Management System 
 
7 A hazard assessment that establishes the worst-case and alternate release scenarios and their impact on the population and the environment (40 CFR Part 68 Subpart B). 
 
7 A prevention program that includes safety information, a hazard review, operating procedures, training, maintenance, compliance audits, and incident investigations. (40 CFR Part 68 Subpart C) 
 
7 An emergency response plan (40 CFR Part 68 Subpart E) 
 
The following subsections discuss details of the plan that has been implemented at the TBR. 
 
RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES 
 
The emergency response policies at this facility ensure that there is emergency response coverage 24 hours per day, 7 days per week.  There are also adequate provisions for coordination with outside 
agencies, such as the Terrel Fire Department and the City of Dallas HAZMAT team, in the event of an emergency.   In the event of a release, plant staff is receiving training to enable an on-site staff response prior to the arrival of the HAZMAT team.   
 
REGULATED SUBSTANCE 
 
The Tawakoni Balancing Reservoir (TBR) uses chlorine as a disinfectant in the water treatment process.  The TBR regularly has a storage maximum quantity of 50 tons of chlorine at its facility that is stored in two 25-ton stationary tanks.  This is above the threshold limit (2,500 pounds) set by the USEPA.  
 
PROCESS DESCRIPTION 
 
The TBR station adds chlorine to the water being transported to the East Side Water Treatment Plant from the balancing reservoir. Water is treated at the plant and subsequently pumped to the distribution network of pipelines, pump stations, and storage tanks.   
 
The existing chlorine feed facility at the TBR consists of  (1) two 25-ton tanks, (2) liquid feed piping and miscellaneous valves,  
(3) three evaporators, (4) gas piping and miscellaneous valves, and (5) three chlorinators.  On treatment plant grounds, the two areas in which chlorine has a potential to generate a gaseous release are the chlorine storage area (items 1 and 2 above) and the chlorine process areas (items 3 through 5 above).  
 
Chlorine is delivered to the TBR by tanker truck. Chlorine is removed from the stationary tanks as a liquid and is withdrawn from one tank at a time through a metal pipe.  As the supply in one tank empties, the supply is manually switched to the full tank.  
 
The chlorine is hard-piped to three chlorine evaporators. The chlorine gas generated by the evaporator is then transferred to the chlorinators.  
 
WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS 
 
The chlorine storage and process areas have associated hazards that can potentially affect on-site employees and the off-site population and environment.  The U.S. EPA requires that one worst-case scenario and one alternate release scenar 
io is reported for each regulated chemical.  
 
Worst-Case Scenario 
 
The largest potential release of chlorine would occur through an angle valve failure on the tank located on the north side of the plant.  This valve failure could potentially release all 90 tons of the chlorine as a gas.  Under Section 68.25(c)(1), the release time for a chemical such as chlorine is 10 minutes.  It was assumed that the scrubber system was not functional, but that the release would be mitigated because the tanks are stored inside.   
 
The EPA-approved modeling program DEGADIS+ was used to characterize the effects of the worst case scenario at the facility.  The distance to the toxic endpoint of 3 ppm was determined to be 4.03 miles.  The estimated affected residential population is 5,435 people.  Residential areas would be affected in the worst-case release scenario. 
 
Alternate Scenario 
 
Two alternate scenarios were modeled for the TBR, neither having any active or passive mitigation.  The first scenari 
o involves a release < of an inch in diameter resulting from a faulty valve.  The leak could occur for about 2 hours.   
 
The EPA-approved modeling program DEGADIS+ was used to characterize the effects of the worst case scenario at the facility.  The distance to the toxic endpoint of 3 ppm was determined to be 1.42 miles.  The estimated affected residential population is 234 people.  Residential areas would be affected in the worst-case release scenario. 
 
The second scenario a break in the fill line during filling of the tank.  The release would occur through a 1-inch diameter hole and last for about 10 minutes.  The distance to the USEPA defined toxic endpoint of 3 ppm was determined to be 3.44 miles.  The estimated affected residential population is 2,218 people.   
 
GENERAL ACCIDENTAL RELEASE PRECAUTION PROGRAM 
 
The TBR carries out consistent operation and maintenance of its chlorine equipment utilizing only fully trained personnel in this area.  TBR management enforces consistent op 
eration through discipline for operational deviations. 
 
FIVE-YEAR ACCIDENT HISTORY 
 
The TBR's accident history was reviewed for a period from June 1994, through June 1999.  During this period of time, no accidental releases of chlorine had occurred.   
 
EMERGENCY RESPONSE PROGRAM 
 
As mentioned earlier, this facility has developed an Emergency Response Program in which plant employees are divided into various management and response teams.  There are five in-plant contacts for an emergency, the Operations Supervisor, and the Shift Supervisors.  The TBR also has a resident operator who can respond to chlorine emergencies after hours.  There are also back-up personnel in the event that the primary response personnel cannot be contacted.   
 
The Emergency Response Plan includes: (1) procedures to follow in the event of a chlorine emergency, (2) information about the frequency of employee emergency response training, and (3) a detailed description of the emergency response training underway. 
 
 
The Terrel Fire Department will contain the area and act as the Incident Commander until trained East Side Water Treatment Plant personnel and the City of Dallas HAZMAT team arrive at the site.  The East Side personnel and the City of Dallas HAZMAT team have been designated to provide back-up emergency responders and equipment, and will assume Incident Command upon arrival to the plan's emergency call.  
 
PLANNED CHANGES TO IMPROVE SAFETY 
 
Based on the hazard review and prevention evaluation completed for chlorine a list of action items was developed and is being considered by TBR management to determine if implementation is to be accomplished.  The most notable planned changes include the following: 
 
7 The evaluation of the need for an automatic kill switch on the tanks.  This would be useful in the case of an emergency when the tanks have to be shut off immediately. A remote switch would eliminate the danger of plant personnel having to shut the chlorine tanks off manually. 
 
7 The MW 
will coordinate with the staff to develop a procedure for how the chlorine truck driver or vendor should perform while on plant grounds.  It is anticipated that the vendor can then be subjected to this procedure at the time of the plant's next bid for chemical purchase.  However, the existing vendor will likely accept these requirements voluntarily to ensure customer satisfaction. 
 
7 DWU will be implementing an upgrade of this area.  The upgrade include improvements such as valve position telemetry that would be tied into the East Side control room, high pressure alarm systems, an upgrade of the evaporators, and remote sensors at the storage tanks.
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