Downingtown RWPCC - Executive Summary
The Downingtown Regional Water Pollution Control Center (DRWPCC) has prepared and implemented a Risk Management Program in accordance with the Chemical Accident Prevention Provisions of 40 Code of Federal Regulations (CFR) Part 68 to prevent chlorine exposure to Downingtown personnel and members of the community, as well as to the environment. This Risk Management Plan (RMP) encompasses all the elements of the Risk Management Program. Accidental release prevention and emergency response policies at the DRWPCC emphasize safety, training, and maintenance. |
The DRWPCC is located in Downingtown, Pennsylvania, 44 miles west of Philadelphia. Chlorine is used to disinfect wastewater prior to discharge to the East Branch of the Brandywine Creek. The facility treats an average flow of 5.2 million gallons per day (MGD) of wastewater. Chlorine at the facility is contained in 1-ton (2,000 lb) containers that are on a standby/on-line basis to ensure the chlorination process is continuous. Chlo
rine is drawn from the 1-ton containers in a gaseous state.
The chlorination process area atmosphere is continuously monitored for chlorine gas leaks, and DRWPCC is equipped with visible and audible alarms to alert personnel that a release has occurred. The DRWPCC preventive maintenance program maintains equipment related to chlorine operations to ensure it is fully operational.
A worst-case release scenario was estimated, per the United States Environmental Protection Agency (EPA) guidance, to provide the greatest distance in any direction to the established toxic endpoint. The worst-case release quantity, established by the regulations, is the greatest amount of chlorine held in a single vessel. In accordance with 40 CFR Section 68.25, it is assumed that the gas is released over a 10 minute period.
No administrative controls or active mitigation measures were included for the worst-case release scenario. Tables from the EPA and Chemical Emergency Preparedness and Prevention Offi
ce (CEPPO) Risk Management Program Guidance for Wastewater Treatment Plants were used to determine the distance to the toxic endpoint for the worst-case release scenario. The facility is considered urban topography due to the buildings, trees, and steep hill to the south, southeast.
The five-year accident history was evaluated to determine a likely alternative release scenario. On April 7, 1997, an operator accidentally disconnected the pigtail from a full container. His respirator was immediately filled with chlorine, and he evacuated the building. The release was controlled by manually reconnecting the pigtail. Based on this scenario and a review of common 1-ton releases, it was determined that the most likely scenario for a container leaking would involve the pigtail. Chlorine gas could potentially be released through the 0.25 inch diameter pigtail, and the container could release approximately 9 pounds per minute of chlorine. Using EPA Guidance Tables, the distance to the to
xic endpoint for this type of release was determined.
The DRWPCC has developed an accidental release prevention program that includes several key elements. DRWPCC is subject to the Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) standard and uses many elements of the PSM in its RMP accidental release prevention program. The primary safe-guard for the chlorine process is the chlorine leak detection system in place at the chlorine building. The leak detection sensor is tested on a monthly basis to ensure it is functioning properly. Operators tour the facility twice a day to ensure the chlorine feed system is functioning properly. Audible and visible alarms are located at the chlorination building and in the operator control room, located in the Control and Sludge Disposal Building.
The DRWPCC plans to add an additional dual head system to detect chlorine in the regulator pressure vent lines. A chlorine leak would be indicated by this system with
a unique beacon color, differentiating a chlorine release from other DRWPCC emergencies. The chlorine regulators have pressure relief valves that vent at the rear of the building should the pressure exceed the setpoint. An interlock device between the alarm and the exhaust fan is in place to shut down the fan when a release is detected, and contain the chlorine inside the chlorine building.
The DRWPCC also has several programs in place to prevent accidental chlorine releases. Specifically, the facility trains operators on the proper operation of the chlorination process, uses state-of-the-art safety equipment, and implements a preventive maintenance program to ensure the process equipment is operating properly.
The DRWPCC has developed and implemented an Emergency Action Plan and an Emergency Operations Plan which contain provisions for trained employees to respond to incidental chlorine releases. However, in the event that the release is beyond the control of the operators, per
sonnel have a mechanism in place to notify the Fire Department for assistance. Equipment available for handling chlorine leaks at the DRWPCC includes Self-Contained Breathing Apparatus (SCBA) and ton container emergency repair Kit 'B' (B Kits). The Local Emergency Planning Committee (LEPC) will provide additional support in the event of an emergency response.