Isabela Wastewater Treatment Plant - Executive Summary
Compaqma de Aguas de Puerto Rico (CAPR) as operator of the Puerto Rico Aqueduct & Sewer Authority (PRASA) system has developed a Risk Management Plan (RMP) for management and prevention of risks associated with the storage and use of chlorine, a regulated toxic substance, at the Isabela Wastewater Treatment Plant. The RMP was prepared in compliance with 40 CFR Part 68 and Clean Air Act (CAA) Section 112(r)(1). The Prevention Program elements build upon the facility's Process Safety Management (PSM) system prepared in compliance with 29 CFR Part 1910.119. |
Accidental Release Prevention and Emergency Response Policies
It is CAPR's policy to comply with applicable Federal and Puerto Rican requirements. The chlorination process at the Isabela Wastewater Treatment Plant uses chlorine, a hazardous toxic substance regulated by EPA, OSHA, and PROSHO. Due to the hazardous characteristics of chlorine, the Isabela Wastewater Treatment Plant observes various safety precautions in the storage,
conveyance and use of chlorine. The safety precautions are necessary to protect employees, contractors, and visitors at the Isabela Wastewater Treatment Plant and the immediately surrounding areas. Safety precautions include procedures and equipment to minimize the potential for accidental release, as well as a written emergency response program for response to any chlorine release that may occur.
The Stationary Source and Regulated Substances Handled
The Isabela Wastewater Treatment Plant provides treatment for up to 2 million gallons per day of wastewater. The regulated substance handled at the Isabela Wastewater Treatment Plant is chlorine.
Chlorine is delivered to the facility via truck in ton containers. The storage building has space for up to eight full containers, a total of 16,000 pounds of chlorine. Chlorine containers are connected to vacuum chlorinators. The chlorinators regulate chlorine use. From the chlorinators, chlorine gas is distributed under vacuum to inj
ectors. The injectors combine the gaseous chlorine with water. The chlorinated water is mixed with the wastewater plant flow for disinfection and odor control.
Worst-case and Alternative Release Scenarios
The worst-case release scenario was determined following EPA's Risk Management Program Offsite Consequence Analysis Guidance. The worst-case release scenario is a vapor release of the entire contents of a ton container over a ten minute period (200 pounds of chlorine per minute). Other worst-case assumptions required by EPA include a low wind speed (1.5 meters per second), stable atmosphere (Class F), urban topography, and no active mitigation of the release.
EPA requires the determination of the area (zone of vulnerability) which may be exposed to a chlorine concentration of 3 ppm or greater. According to the American Industrial Hygiene Association, 3 ppm is the maximum concentration of chlorine in air below which nearly all people could be exposed for one hour without serio
us health effects. Based on the worst-case assumptions, the zone of vulnerability was determined to extend 1.3 miles from the chlorine storage area.
The following are known to be within the zone of vulnerability for the worst-case release scenario: residences, hospital, schools, and recreation areas (river and beach).
Approximately 9,900 residents are located within a 1.3 mile radius of the chlorine storage area. Many of these residents would not actually be impacted in even a worst-case release, as the chlorine would travel in the direction of wind. No known environmental receptors (such as state parks or officially designated wildlife preserves) are located within the zone of vulnerability.
The conditions and parameters for the worst-case scenario are specified by EPA. A more realistic alternative release scenario was examined, also following EPA's Risk Management Program Offsite Consequence Analysis Guidance. The alternative release scenario is a vapor release of the entir
e contents of a ton container through a broken 3/8 inch flexible connector tube. If the container was not shut off, the contents would be released at a rate of 21 pounds of chlorine per minute over a 95 minute period. More typical weather conditions are also used (wind speed of 3.0 meters per second, atmospheric stability Class D). Other conditions remain the same as in the worst-case scenario (urban topography and no mitigation of the release).
The zone of vulnerability for the alternative release scenario is determined to extend 0.1 miles from the chlorine storage area. Approximately 100 residents are located within a 0.1 miles radius of the chlorine storage area. These residents could be impacted, depending on the direction of wind. No known environmental receptors are located within the zone of vulnerability.
General Accidental Release Prevention Program and Chemical-specific Prevention Steps
CAPR complies with PROSHO requirements for Prevention Programs and for Process Sa
fety Management. Operators, maintenance staff and contractors are informed of chlorine hazards, and hazard signs are posted in the chlorine storage area. Standard operating and maintenance procedures have been developed, and employees who work with chlorine are provided training.
Emergency Response Program
CAPR has an emergency response program. Chlorine gas detectors are located within the storage area for early detection and warning of any leak. Leak repair kits are maintained on site, and operators are trained in how to quickly stop any leak that may occur. The emergency response program is coordinated with Civil Defense for notification of the public.
CAPR periodically conducts various training programs, including emergency response training. All CAPR facilities are scheduled to receive refresher training by September 30, 1999.
Five-year Accident History
One accident resulting in the unplanned release of chlorine gas in excess of 10 pounds has been recorded in the past f
ive years. On June 12, 1995 there was a release of unknown duration of an unknown quantity from a broken flexible connector tube. No injuries resulted from this leak. The cause of this leak was investigated and the flexible connector tube was replaced to prevent further releases.
Planned Changes to Improve Safety
CAPR uses Process Hazard Analyses (PHA) to identify and recommend changes to ensure a high level of safety. Issues identified from a PHA are then addressed in CAPR's Prevention Program. Assessments of the chlorine processes were conducted during April and May 1999 for each CAPR facility. Documentation of the formal PHA for this facility will be completed by July 20, 1999. An audit of the RMP and PSM programs will be conducted within three years to verify the effectiveness of the program.