FKAA / J. ROBERT DEAN WATER TREATMENT PLANT - Executive Summary
The Florida Keys Aqueduct Authority (FKAA) complies with all applicable procedures and requirements of the U.S. Environmental Protection Agency's (EPAs) Risk Management Rule (RMPR). The RMPR was established to reduce the risk to employees and the public of injury or death from accidental release of chemicals. The FKAA recognizes the risks associated with hazardous chemicals at the J. Robert Dean Water Treatment Plant (WTP) facility. The FKAA has developed a comprehensive Risk Management Plan and Program (RMPP) to address safety, prevention, and emergency response. The RMPP has also ensured that in the unlikely event of a release, local area emergency responders (local emergency response commission and fire department) and other authorities are fully trained and ready to engage specific plans to remediate the situation quickly. |
The FKAA J. Robert Dean WTP is located in a pineland preserve west of Florida City in Dade County. The WTP uses chlorine as part of the disinfection treatm
ent process that provides safe drinking water to the residents of the Florida Keys. Chlorine has been used safely for years to disinfect drinking water and reduce or eliminate the risk of such waterborne diseases as cholera, typhoid, and dysentery. Chlorine is listed in the EPAs RMPR. The FKAA handles a maximum inventory of 12-ton chlorine cylinders at the WTP. The WTP is manned 24 hours a day by trained personnel. Certified WTP operators perform daily inspection of the chlorine storage and equipment area and respond to any trouble alarms which may occur.
The RMPR requires the analysis of two offsite consequence scenarios. The two scenarios are identified as the "worst case release" and "alternative release". The first scenario is defined by EPA, which states that "the owner or operator shall assume that the ... maximum quantity in the largest vessel.. is released as a gas over 10 minutes," due to an unspecified failure. The alternative scenario is defined as "more likely to o
ccur than the worst-case release scenario".
Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine gas released before its concentration decreases to the "toxic endpoint" selected by EPA of 3 parts per million (ppm), which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as 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 distance has to be defined, "to estimate the population potentially affected".
The worst-case release scenario at the FKAA J. Robert Dean WTP involves a catastrophic failure of the one ton cylinder due to
corrosion, impact or construction defects. The offsite consequence analysis for this scenario was performed using the EPA's OCA Guidance reference table with conditions pre-defined by EPA. The pre-defined conditions assume an atmosphere of Stability Class F, wind speed of 1.5 meters per second, a temperature of 77 Fahrenheit, and are applicable for any relative humidity. The entire contents of the chlorine cylinder are assumed to be released in a 10 minute duration (200 pounds/minute). Since more than 50% of the terrain was rural, a rural topography was assumed. The affected population within a specified radius was determined using Landview III (1990 Census Data). Using the EPA's OCA Guidance reference table, a distance to toxic endpoint of 3.0 miles and an estimate of residential population potentially affected of 19,000 within the 3.0 mile radius was obtained. The affected population used may be unrealistic because only the population within an elliptical plume extending downw
ind of the release point is potentially affected.
The alternative release scenario involves a chlorine gas pipe leak between the one ton cylinder and the vacuum regulator/check unit. This small section of pipe is the only portion of piping which is under pressure. The remaining piping is under a vacuum system. When vacuum system is broke, the vacuum regulator/check unit closes preventing chlorine gas from escaping vacuum system. the alternate release scenario from the EPA's OCA Guidance reference table assumes an atmosphere of Stability Class D, wind speed of 3.0 meters per second, relative humidity of 50%, temperature of 77 Fahrenheit, and a rural topography. The total amount of chlorine gas released was assumed 317 pounds in a 60 minute duration with a maximum sustained release rate of 10.5 pounds/minute. Using the EPA's OCA Guidance reference table, a distance to toxic endpoint of 0.6 miles and an estimate of residential population potentially affected of 6 within the 0.6 mil
e radius was obtained.
If an accidental release of chlorine gas occurs and a concentration of 1ppm of chlorine gas is detected in the air, the chlorine detectors in the storage area will sound alarms. The WTP operators are trained to safely to the alarms.
The general FKAA J. Robert Dean WTP accidental release prevention program is based on the following key elements:
*High level of operator training
*Preventive maintenance program
*Routine review of operating procedures, process and safety equipment, and process hazard
The FKAA J. Robert Dean WTP has an emergency response program which is provided annually to the Local Emergency Response Commission and the MetroDade Fire Department. The MetroDade Fire Department performs annual surveys of the WTP. Emergency response drills are reviewed and conducted a minimum of once a year.
No accidental releases of chlorine gas have occurred at the FKAA J. Robert Dean WTP in the past five years. The FKAA plans to continue improving its Risk
Management Plan and Program and enhancing employee and public safety through prevention and emergency response programs.