South Water Purification Plant (SWPP) - Executive Summary
CHLORINE RISK MANAGEMENT PROGRAM (RMP) |
CITY OF CHICAGO
DEPARTMENT OF WATER
South Water Purification Plant (SWPP)
June 9, 1999
The South Water Purification Plant (SWPP) treats water to potable drinking standards for the City of Chicago and many surrounding communities. The plant uses chlorine to disinfect water from Lake Michigan. The plant stores more than the threshold quantity of 2,500 lbs of chlorine onsite. The
disinfection process is the only process at the South Plant subject to United States Environmental Protection Agency (USEPA) Risk Management Program (RMP) regulations codified in 40CFR Part 68. Chlorine is an easily liquefiable greenish-yellow gas with a pungent, irritating odor. It is listed by the USEPA as a regulated toxic substance for release prevention. Chlorine is safe to use as a drinking water disinfectant under regular plant conditions when handled with appropriate care.
SWPP Chlorine Process
Liquid chlorine is trucked to the p
lant site in 1-ton (2,000 lbs) pressurized containers by an outside vendor. Liquefied chlorine in the containers is changed to gas-phase chlorine with evaporators. Chlorine gas is mixed with water at different application points for disinfection as part of the water treatment process.
SWPP Release Prevention and Emergency Response Policy
The City of Chicago Department of Water (DOW) in concert with SWPP management is committed to manage and operate the plant in accordance with relevant USEPA regulations and general good operating practices to ensure minimum risk of a chlorine release from the disinfection process. The DOW has voluntarily implemented an Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) program for the SWPP chlorine process although it is not explicitly subject to this federal program. In order to ensure periodic monitoring and continual evaluation of the RMP/PSM program elements being implemented at the plant, the DOW has instituted
an emergency response (ER) organizational structure within the Department and SWPP. In addition to their regular duties, members of this structure have additional RMP/PSM-related responsibilities for the long-term management of the RMP/PSM program.
Worst-case Release Scenario
As required by USEPA regulations, the worst-case release scenario was assumed to be the complete loss of contents of a 1-ton chlorine container during unloading operations that are performed outdoors. In this facility, chlorine containers are unloaded and stored outdoors. For this analysis no passive
mitigation measures were assumed. The USEPA guidance for defining a worst-case release scenario for unmitigated release of gas is to estimate the release rate over a 10-minute period of the largest quantity resulting from a pipe or vessel failure. Thus, the chlorine emission rate from the worst-case release scenario used was the loss of 2,000 lbs of chlorine averaged over a 10-minute period, i.e., 200 lbs/min. US
EPA's public-domain RMP*Comp model was used to determine the distance to the toxic endpoint of 0.0087 mg/lit (or 3 ppm). The toxic endpoint distance does go offsite. It should be noted that the potential offsite impact due to a release is greatly minimized on account of the location of SWPP which is bounded by Lake Michigan on the north and east. Since almost 50 percent of the area within the circle of influence defined by the distance to the toxic endpoint as the radius is over Lake Michigan, potential offsite impacts are greatly reduced.
SWPP employees thoroughly inspect every chlorine container for potential leaks and overall structural integrity upon delivery and prior to process hookup. Chlorine sensors and a system of emergency alarms at strategic locations around the chlorine process initiate the emergency response procedures (i.e., release abatement and evacuation) that includes activation of the emergency caustic scrubber to neutralize potential chlorine releases. This mini
mizes the chance that a container will fully discharge its contents in a release and minimizes the potential for an offsite impact.
Alternative Release Scenario
The following three most likely alternative scenarios (ranked in order of probability of occurrence) were identified:
- Case (1): Container valve failure;
- Case (2): Shear of pigtail containing liquid chlorine; and
- Case (3): Over-pressurization of rupture disk
The above alternative cases were modeled using USEPA's public-domain RMP*Comp model to determine the distance to the toxic endpoint of 0.0087 mg/lit (or 3 ppm). Effects of both passive mitigation (due to building enclosure) and active mitigation afforded by the SWPP scrubber system were included in the analysis. The maximum toxic endpoint distance does go offsite, but only by a few hundred feet. It should be noted that any potential offsite impact due to a release is greatly minimized due to SWPP's location, which is bounded by Lake Michigan on the north and east.
As noted above, SWPP employees thoroughly inspect every connection from the chlorine container to the liquid piping for potential leaks and overall structural integrity prior to hookup. In addition, SWPP has regular operation and maintenance procedures for evaluating and replacing, if required, container valves and rupture disks. Also, the plant has chlorine sensors and a system of emergency alarms at strategic locations around the chlorine process that initiate the emergency response procedures (i.e., release abatement and evacuation) that includes activation of the emergency caustic scrubber to neutralize potential chlorine releases. This minimizes the chance for a discharge of quantities of chlorine which could result in an offsite impact.
Release Prevention Program
As a municipal organization SWPP is not subject to OSHA regulations. However, SWPP has proactively implemented an OSHA Process Safety Management (PSM) program (codified in 29CFR Part 1910.119) for the chlorine process.
The scope of the PSM program encompasses various facets of release prevention, e.g., it engenders employee participation, increases employee awareness about the hazards of handling chlorine, establishes safe standard operating procedures and enhances access to process safety information. In December 1998, SWPP performed a PSM audit and a HAZOP process hazards analysis (PHA) on the chlorine system with the help of outside consultants in order to review existing operating procedures, equipment maintenance schedules, operational safeguards and identify action items to render the process safer. Following the PHA, SWPP developed a written PSM program along with an updated O&M (Operations and Maintenance) Manual with the help of outside consultants. The written PSM program
provides the procedural backbone for safe operability functions (i.e., continual review of safe operating procedures, review of mechanical integrity of equipment, improved maintenance schedules, increased training, bet
ter access to process safety information and hazard awareness for both employees and onsite contractors, and effective emergency response planning), and allows SWPP to maintain, review and evaluate the program on a periodic basis.
Five-year Accident History
SWPP has had no reportable chlorine releases in the past five years (6/94 - 6/99). The South Plant has been operational since 1946. Since that date there have been no serious onsite injuries, no offsite injuries and no offsite environmental damage due to a chlorine release.
Emergency Response Program
Since SWPP has adopted the OSHA PSM program, the plant has updated existing procedures for Emergency Planning and Response to conform to applicable PSM regulations. SWPP has adapted the PSM Emergency Response Plan so that it also satisfies RMP Part 68 requirements.
SWPP has a well delineated emergency response (ER) organization under the command of the emergency response coordinator (ERC) with a set of clearly defined responsibilit
ies and procedures for ER team members. ER team members are regularly evaluated, receive updated training and conduct practice emergency response drills. Besides onsite training and practice, ER team members are responsible for coordinating emergency response activities (e.g., agency notifications) with local emergency responders such as the Chicago Fire Department, Illinois Emergency Management Agency (IEMA) and the National Response Center (NRC) through established channels of communication. The Emergency Response Plan contains detailed notification procedures to be followed by ER team members.
SWPP has detailed onsite evacuation procedures customized for the plant in the event of a release of chlorine. SWPP is equipped with appropriate emergency response equipment in readiness for immediate application. The Local Emergency Planning Committee (i.e., the Chicago Fire Department) is responsible for addressing all offsite emergency activities.
The City of Chicago Department of Wate
r (DOW) and SWPP management are committed to supporting the emergency response (ER) organization and its prescribed functions. ER team members are drawn from the existing employee pool and the organizational concept fosters pride and emphasizes concerns for safe operation of the plant. The well defined ER organization at SWPP operating in conjunction with the Chicago Fire Department alleviate safety concerns about handling chlorine at the plant.
Changes to Improve Safety
The DOW is currently completing minor upgrades to improve the chlorine system. Also modifications to the plantwide communications system are underway and will be completed by the end of 2001. A full upgrade of the SWPP chlorine system including new piping and equipment, full enclosure of the loading dock, and emergency scrubber improvements is anticipated within the next five years. Thus, in addition to improved operating and safety procedural changes, upgrades to the chlorine system demonstrate the commitment to saf
ety that the DOW has made to both plant employees and the surrounding community.