Hillsborough River Water Treatment Plant-Tampa FL - Executive Summary

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a.  The City of Tampa Water Department (TWD) accidental release policy involves a unified approach that integrates technologies, procedures, and management practices.  All applicable federal and state prevention program guidelines are adhered to.  The TWD emergency response policy involves the preparation of response plans which are tailored to each facility and to the emergency response services available in the community.  Emergency response plans include coordination with the local fire departments and COT emergency response units. 
b.  The HRWTP is a surface water treatment facility producing potable water from the Hillsborough River is Tampa, Florida, utilizing an enhanced coagulation treatment process. HRWTP maintains an inventory of liquid chlorine in two 90 ton rail cars located within an enclosed chemical building.  Chlorine is used as the primary disinfectant in t 
he potable water treatment process.  Secondary disinfection for potable water storage and distribution is achieved with chloramine, a combination chlorine and anhydrous ammonia.    Anhydrous ammonia is stored in two 2000 gallon horizontal pressurized tanks. .  Anhydrous ammonia storage tanks are filled only to 85% capacity as required under manufacturer specifications.  Each tank has a maximum weight storage capacity of 9,675 pounds of anhydrous ammonia.  The treatment facility is currently manned 24 hours per day, 7 days per week.  The HRWTP has been designed for the safe storage and handling of chlorine and ammonia as referenced in the Combined Process Safety Management Program for the City of Tampa Water Department, Production Division.  These are the only chemicals used in a process at this facility covered by the RMP rule. 
c.  The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative case releas 
e", and one "alternate case release" for anhydrous ammonia.  The "worst case release" scenario is defined by EPA as "a chemical  release of the maximum quantity in the largest vessel released in a 10 minute period", due to an unspecified failure.  The alternative release scenario is defined as "more likely to occur than the worst case release scenario". 
Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint' selected by EPA under the Emergency Response Planning Guideline 2.   The defined endpoint used for chlorine was the ERPG2 concentration of 3 PPM chlorine.  The Emergency Response Planning Guideline 2 (ERPG2) is "the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability 
to take protective action".   The residential population within a circle with a radius corresponding to the toxic endpoint has to be defined to "estimate the population potentially effected. 
For the processes of chlorine and anhydrous ammonia at the HRWTP, distances to the toxic endpoints are concentric, with liquid chlorine release having the greatest distance to the toxic endpoint.  Therefore, a chlorine release was modeled for the worst case scenario.  The worst case release scenario for a chlorine release at HRWTP would be the instantaneous release of one full railcar in a ten minute period.  The amount of chlorine released would be 180,000 pounds.  Release conditions are defined in the RMP rule to be an atmospheric stability factor F, wind speed @ 1.5 m/s, and a roughness coefficient set for urban.  Mitigation for an enclosed building considered to be accessed at 55% of the released quantity.  Under this condition a mitigated release quantity would be 99,000 pounds of chlorine.  
For the ten minute release period the release rate would be 9,900 pounds per minute.  EPA's RMP*Comp dispersion program was used to determine the distance to the toxic endpoint for this scenario.  The area of concern distance radius to the ERPG2 endpoint is 9.9 miles. 
An alternative release scenario was developed for both chlorine and ammonia at HRWTP.  
Liquid chlorine is transferred from the railcar in service to the chlorine evaporator thru a 1 inch diameter pipe.  A rupture of the transfer piping will create a "flashing liquid" chlorine release.   The release rate for "flashing liquid releases" for chlorine as referenced in EPA Risk Management Program Guidance for Wastewater Treatment Plants;  EPA 550-B-98-010, equation (8), page 4-22 as:  QR= 3,140 X Ah. 
QR= Release rate in pounds per minute 
Ah= Hole or puncture area (sq in)= 3.1416 x (12)/4 = 0.79 sq in. 
QR = 3,140 x 0.79 = 2,481 #/min. 
Release conditions are set at default conditions for the RMP rule.  These are  ambient te 
mperature default at 25 degC, atmospheric stability factor D, wind speed @ 3.0 m/s,  roughness coefficient set for urban.  Mitigation for enclosed building considered at 55% of the release quantity would yield a release rate of  1,364 #/min .  Utilizing EPA's RMP*Comp modeling program the distance to the toxic endpoint for the alternative chlorine release scenario is 0.6 miles.                                                                                              Note: For the alternative release explained above to occur, a failure of the rail car excess flow check valve would also have to occur.  The excess flow check valve of  the chlorine rail car is designed to prevent flow of liquid chlorine from the rail car is excess of 250 pounds per minute.  If a piping rupture as described above were to occur, the excess flow check valve on the chlorine car angle valve feeding liquid chlorine from the rail car would shutdown flow when a flow rate of 250 pounds per minute was reached.  I 
n the case described above this would occur within the first 15 seconds of a pipe rupture significantly reducing the release of chlorine from the rail car.  The excess flow valve would remain closed until sufficient pressure was restored to the feed line.  This would not occur until the feed line was repaired.  Under this alternate case release scenario, the distance to the toxic endpoint would be 0.2 miles as computed by RMP*Comp ver 1.06.  
For anhydrous ammonia the alternative case release scenario involves the rupture of a 2 inch diameter stainless steel transfer piping carrying ammonia gas.  As summarized in section 8.1 of the OCA Guidance manual, the release rate can be estimated by the following equation. 
QR= HA x  Pt x GF  /  (Tt)**0.5  = 254.7 #/min. 
QR= Release rate in pounds per minute 
HA= Hole or puncture area (sq in)= 3.1416 x (2**2)/4 = 3.14 sq in 
Pt=   Tank Pressure (psia) = 100 psia for ammonia vapor pressure @ 25 degC 
Tt=   Tank Temperature in degK = 273 + d 
egC= 273 + 25= 298 
GF= Gas factor as indicated from Exhibit B-1, Appendix B of OCA Guidance manual= 14 for                 anhydrous ammonia. 
Utilizing EPA's RMP*Comp modeling program the distance to the toxic endpoint for the alternative ammonia release scenario is 0.2 miles, to a ERPG-2 toxic endpoint concentration of 200 ppm.  There are currently no passive mitigation systems in place for anhydrous ammonia.  However, ammonia leak detectors are being tested to enhance operator response time to an ammonia leak situation. 
d.  The TWD accidental release prevention program is based upon the following key elements: 
DESIGNING for Safety... 
    Chlorine rail car construction meets federal guideline 49CFR179.102. 
    Excessive-flow check valve prevents rapid release of rail car contents .  
    Chlorine rail car enclosed in containment building. 
    Containment building has high volume air blower. 
    Four automatic chlorine gas detector alarms. 
    Annunciator panel status/alarm on 16 che 
    Emergency shutoff actuator on rail car transfer valve.  
    Ammonia tanks constructed to ASME Code or unfired pressured vessel. 
    Ammonia tanks equipped with duel pressure relief valve and liquid level sensor. 
    All ammonia piping Type 316 stainless steel with fittings suitable for 300 psi service. 
    Ammonia detector alarms mounted around tanks. 
MAINTAINING Safe Operations... 
    Equipment check performed on routine schedule. 
    Maintenance personnel training is State certified. 
    Pre-startup safety review for all process changes. 
    Annual inspection of all critical devices. 
    Maintenance staff trained in Process Safety Management. 
    Safety review of process systems by manufacturer's Technical Product Specialist. 
OPERATING Safely... 
    Written standard operating procedures for all process systems. 
    Operators are trained and State certified by DEP. 
    Process Monitoring and Control System computer provides continuous monitoring of all  processes with   alarm setpoints. 
    Operation personnel follow OSHA Process Safety Management Plan. 
    Established and tested Emergency Preparedness Plan. 
    Continuous camera surveillance from control room. 
    Operators trained in the use of Self Contained Breathing Apparatus (SCBA) available on site. 
AUDITING our Operations 
    Critical equipment/instrumentation tested and calibrated by I&C group per PM schedule. 
    Process Hazard Analysis conducted per PSMP. 
    Monthly safety review by Plant Safety Committee. 
    Process Safety Management audits performed. 
e.  No accidental releases of chlorine or anhydrous ammonia have occurred at this facility in the past five year period. 
f.  The facility has an emergency response program which has been coordinated with the Tampa Fire Department, Emergency Operations Center for Hillsborough County, and the Local Emergency Planning Council Region 8.  This program includes an emergency response decision tree and notification plan.  Operators are trained in the use of SCBA, and each op 
erator has been issued and is trained in a class B chemical suit.  The facility has on line leak detectors for chlorine strategically located at storage and feed application points with audible alarms on the plant site, and computer alarm setpoints back to the SCADA control system in the operations control room.  Automatic air activated actuator valve shutdown devices are being installed on railcar feed valves.  The actuators will automatically close chlorine rail car valves at the first detection of a chlorine leak.  Ammonia leak detector are being evaluated on site for the same purpose of achieving automatic shutdown at the ammonia storage tank at first detection of an ammonia leak. 
g.  This facility is currently undergoing a 12 million dollar automation and instrumentation upgrade to be completed in November 1999.  New equipment, including chlorine evaporators and chlorinators, automated ammonia feed systems, in addition to the automatic shutoff devices for chlorine rail cars and r 
emote shutdown of ammonia at the feed tanks are to be installed.  Operational protocol meeting the regulated guidelines of the OSHA Process Safety Management Plan have been implemented at this site.
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