City of Tampa Morris Bridge Water Treatment Plant - Executive Summary
EXECUTIVE SUMMARY |
RISK MANAGEMENT PLAN
CITY OF TAMPA WATER DEPARTMENT
MORRIS BRIDGE WATER TREATMENT PLANT
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 tailed 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 Morris Bridge Water Treatment Plant (MBWTP) is a ground water treatment facility producing potable water from the Morris Bridge Wellfield in Tampa, Florida, utilizing a lime softening treatment process. MBWTP maintains an inventory of 40,000 pounds of chlorine in twenty one ton chlorine cylinders located within an enclosed chemical buildi
ng. Chlorine is used as the primary disinfectant in the 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 one 2000 gallon horizontal pressurized tank. Anhydrous ammonia storage tanks are filled only to 85% capacity as required under manufacturer specifications. This tank has a maximum weight storage capacity of 9,675 pounds of anhydrous ammonia. This is below the threshold limit for anhydrous ammonia under the RMP rule and is not included in this RMP. The treatment facility is currently manned 24 hours per day, 7 days per week. The MBWTP 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. Chlorine storage at MBWTP is the only chemical used in a process at this facility covere
d by the RMP rule.
c. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative case release". 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 exp
eriencing 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 eh toxic endpoint has to be defined to "estimate the population potentially effected.
Worst -case release scenario:
There are twenty one ton chlorine cylinders stored in the chlorine building at MBWTP. Ten of the one ton cylinders are active at one time incorporated into two banks of 5 one ton cylinders each feeding a common manifold line. Worst case release criteria under RMP regulations specifically state the release of the full contents of the largest storage vessel or line in a ten minute period. For MBWTP this would be the release of a single one ton cylinder in ten minutes. Mitigation for a building enclosure is set at 55% of the total release quantity. For a one ton cylinder the mitigated release quantity would be 1,100 pounds of chlorine.
ease rate can be calculated from the following equation:
QR- Release rate in pounds per minute
QS- Release quantity in pounds
QR= 2,000 # / 10 minutes
QR= 200 #/min
Mitigation factor for an enclosed building is considered at 55% of the release rate.
QR= 200 #/min X 0.55 = 110 #/min
The model output used was EPA RMP*Comp, version 1.06, dispersion program. 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.
Results obtained for the EPA RMP*Comp model were as follows:
Distance to the toxic endpoint for chlorine ( 3ppm), was 0.9 miles.
Alternate case release scenario:
Gas chlorine is transferre
d from each one ton cylinder bank ( 5- one ton cylinders per bank) into a common 3/4" diameter piping manifold and fed by pressure to one of two on line chlorinators. A rupture of the manifold transfer piping will create degassing of chlorine into the enclosed building. Release conditions are: ambient temperature default at 25 degC; stability factor D; wind speed @ 3.0 m/s; roughness coefficient urban; mitigation is considered for the enclosed building at 55%.
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
QR= Release rate in pounds per minute
HA= Hole or puncture area (sq in)= 3.1416 x (0.75**2)/4 = 0.44 sq in
Pt= Tank Pressure (psia) = 113 psia for chlorine vapor pressure @ 25 degC
Tt= Tank Temperature in degK = 273 + degC= 273 + 25= 298
GF= Gas factor as indicated from Exhibit B-1, Appendix B of OCA Guidance manual= 29 for chlorine.
QR = (0.44) x 113 x 29 /
298**0.5 = 83.5 #/min
With mitigation for enclosed building at 55%, the adjusted release rate is;
QR= 83.5 #/min x 0.55 = 45.9 #/min
RESULTS: Model: RMP*Comp, Ver 1.06
Plume distance to endpoint (3 ppm): = 0.1 miles
Note: At this endpoint there are no public receptors with the area of concern at this time.
d. The TWD accidental release prevention program is based upon the following key elements:
DESIGNING for Safety...
One ton cylinders are fabricated to DOT specification 106A500X.
Ton cylinders equipped with six fusible metal pressure relief plugs.
Chlorine ton cylinders enclosed in containment building.
Containment building has high volume air blower.
Automatic chlorine gas detector alarms.
Emergency shutoff valves to be installed on ton cylinder manifold system.
MAINTAINING Safe Operations...
Equipment check performed on routine schedule.
Maintenance personnel training is State certified.
Pre-startup safety review for all process changes.
tion of all critical devices.
Maintenance staff trained in Process Safety Management.
Safety review of process systems by manufacturer's Technical Product Specialist.
Written standard operating procedures for all process systems.
Operators are trained and State certified by DEP.
Process Monitoring and Control System computer will 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.
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 fac
ility 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 operator has been trained in use of a "class B" Chlorine Institute emergency repair kit for one ton cylinders. The facility has on line leak detectors for chlorine strategically located at storage and feed application points with audible alarms on the plant site. The Process Monitoring and Control System computer will allow alarm setpoints back to the PMCS control system in the operations control room. Automatic air activated actuator valve shutdown devices are being installed on each one ton cylinder on line. The actuators will automatically close the chlorine feed valve on the one ton cylinder at the first detection of a chlorine leak.
g. This f
acility is part of the 12 million dollar automation and instrumentation upgrade project at the TWD Production Division to be completed in November 1999. New equipment will include chlorine evaporators and chlorinators, automated ammonia feed systems, in addition to the automatic shutoff devices as described above. Operational protocol meeting the regulated guidelines of the OSHA Process Safety Management Plan have been implemented at this site.