City of Erie, PA - Wastewater Treatment Plant - Executive Summary
The City of Erie Wastewater Treatment Plant (WWTP) is committed to minimizing the risk to employees and to the public of injury or death from an accidental release of chlorine. Chlorine gas is the only regulated substance at the WWTP and is used for disinfection of the City's effluent stream prior to discharge. Liquid chlorine is piped from a railroad tank car to an evaporator that converts the chlorine to a gas. The chlorine gas flows to the chlorinator which dissolves the gas in water and forms a dilute liquid chlorine, which becomes the disinfection agent. The maximum amount of chlorine in this process at any one time is 180,000 pounds. This represents the volume in a full railroad tank car. This amount exceeds the threshold for EPA's Risk Management Planning of 2500 pounds. There are possible offsite consequences from a chlorine release, but the facility is not covered by OSHA's process safety management standard. Therefore, the Erie WWTP is only subject to risk management |
program level 2.
The Erie WWTP maintains up-to-date, accurate, written operating procedures that provide clear instructions for the chlorine process. These operating procedures are instrumental in ensuring safe operation of the systems and preventing accidental releases. An equipment failure could also result in an accidental release. The WWTP has a maintenance program that is also critical to maintain the on-going mechanical integrity of the process equipment. The Process and Operations Superintendent ensures that all chlorine process safety information is kept up-to-date, and maintained in a format that provides easy access for employees.
The Process and Operations Superintendent ensures that all operators have the required training to properly and safely operate the chlorine process. All new employees must complete at least 8 hours of initial training, which consists of chlorine specific safety and health hazards, process operations, and emergency operations including shutdow
n. Each employee must also complete at least 4 hours of refresher training every three years. The refresher training covers a review of all topics presented in the initial training, as well as any changes to the chlorine process or equipment. Written examinations are given to evaluate the employees' proficiency following the training sessions.
Hazard reviews are conducted to identify, evaluate, and control the risk associated with process hazards and chlorine release scenarios. The overall purpose is to prevent or minimize the effects of a release. The hazard review is conducted on the entire chlorine system. The Process and Operations Superintendent updates the hazard review at least once every five years, or when a major change occurs in the process.
A chlorine gas leak to the atmosphere is the primary hazard associated with this process. The worst case scenario would be represented by the complete failure of the railroad tank car, releasing 90 tons of chlorine into the air.
Using EPA's guidance criteria, this release is calculated to take place over 10 minutes. At a wind speed of 3.4 mph, the chlorine gas would travel more than 25 miles before the concentration drops below the toxic endpoint, the level at which chlorine gas is no longer a hazard to the public. Depending upon the wind direction, such a release could affect everyone within Erie County, part of northern Crawford County and part of western Chataqua County, New York. The population within a 25 mile radius of the WWTP was estimated to be 226,076 people. This was determined using the "LandView" computer software developed by the EPA and NOAA (National Oceanic and Atmospheric Administration).
Numerous alternate release scenarios resulting from the failure of valves or broken piping were considered. Different variables were used in evaluating each different situation. These include the size of the opening, pressure and release duration. The "alternate release" scenario chosen represents
a more plausible possibility than the loss of the complete railroad car. This situation involves damage to the 2-inch piping that connects the railroad car and the evaporator in the chlorine room. This would allow liquid chlorine to escape uncontrolled from the pipe estimated time of one-half hour. There are automatic controls to close off the valve at the railroad car, but he volume in the piping could still escape to the environment. The volume contained in the pipe is 2276 pounds, and the time for a response from the Erie fire department is estimated to be 30 minutes. This scenario assumes that the 2276 pounds escapes over the 30 minute time period at 76 pounds per minute. Using EPA's guidance criteria, with a wind speed of 6.7 mph, the chlorine gas would travel 0.4 miles before the concentration drops below the toxic endpoint. The population within a 0.4 mile radius of the WWTP was estimated to be 2114 people. This was determined using the "LandView" computer software deve
loped by the EPA and NOAA (National Oceanic and Atmospheric Administration).
During the past five years, there has been only one accidental release from the Erie WWTP in which chlorine escaped offsite. On 9/20/1995, a section of piping broke releasing about 600 pounds of liquid chlorine. The chlorine went to a gaseous state and was carried to the north by the wind. The Erie fire department and hazmat were notified and they responded. The northern area surrounding the plant has no residential population, and there was no need for an evacuation. The hazmat personnel then cleaned up the area.
In the event of an accidental release, the WWTP emergency action plan contains the procedures for evacuation of the plant and immediate notification of the fire department. The fire department is responsible for control of the chlorine leak and evacuation of any affected residents. The fire department has a copy of the WWTP risk management plan and conducts inspections to review plant operat
ions, equipment and procedures.