Norwich Wastewater Treatment Plant - Executive Summary
Norwich Public Utilities (NPU) owns and operates the Norwich Wastewater Treatment Plant (WWTP) located at 44 Falls Avenue in Norwich, Connecticut. This facility, as a user of chlorine in excess of regulated thresholds, is subject to the Occupational Safety and Health Administration's (OSHA's) Process Safety Management (PSM) regulations, as promulgated under 29 CFR 1910.119, and the United States Environmental Protection Agency's (EPA's) Risk Management Program (RMP) regulations, as promulgated under 40 CFR Part 68. |
The NPU and it's employees all share in the responsibility for the health and safety of NPU employees, contractors, and general public. The goal of this risk management program, as endorsed by all levels of management within NPU, is to prevent accidental releases of substances that can cause serious harm to the public and the environment from short-term exposures to chlorine and to mitigate the severity of releases that do occur. The 1990 Amendments to the Clean Air Act (C
AA) require EPA to issue a rule specifying the type of actions to be taken by facilities (referred to in the statute as stationary sources) to prevent accidental releases of such hazardous chemicals into the atmosphere and reduce their potential impact on the public and the environment.
The NPU WWTP in Norwich, Connecticut utilizes chlorine in their Chlorination Process in which chlorine gas is introduced during the wastewater disinfection process under controlled conditions. The facility typically will have an inventory of eight (8) 2,000-lb cylinders of which four (4) will be connected to the Chlorination Process at any one time. Two (2) cylinders are actually "open" to the system while the Chlorination Process is underway. The Chlorine Storage Room is located on the interior of the Sludge Handling building. The Chlorination Process is conducted in the Chlorine Room which is within the same building interior adjacent to the Chlorine Storage Room.
NPU was required to conduct an of
fsite consequence analysis to provide information to the government and the public about the potential consequences of an accidental chemical release at your facility. The offsite consequence analysis (OCA) consisted of two elements:
7 A worst-case release scenario
7 Alternative release scenarios.
To simplify the analysis and ensure a common basis for comparisons, EPA has defined the worst-case scenario as the release of the largest quantity of a regulated substance from a single vessel or process line failure that results in the greatest distance to an endpoint. In broad terms, the distance to the endpoint is the distance a toxic chlorine vapor cloud will travel before dissipating to the point that serious injuries from short-term exposures will no longer occur. The toxic endpoint for chlorine is 0.0087 mg/L.
At the NPU WWTP, chlorine is present in one-ton (2,000-lb) cylinders. The worst-case scenario assumes that this quantity is completely released over a period of 10 minutes (e.
g., a 2000-lb worst case corresponds to a 200-lb/min rate of release). The predicted distance to the toxic endpoint for this scenario within an urban environment is 1.3 miles, based on look-up tables provided in EPA's guidance document entitled "Risk Management Program Guidance for Wastewater Treatment Facilities". This release would impact a relatively medium residential population surrounding the WWTP, some schools, hospitals, and commercial/industrial facilities.
The potential alternative scenario selected involves the release of liquid chlorine from a small hole (1/16 inch diameter) in a pipe or vessel. This would provide a continuous release of chlorine at a rate of 10 lbs/minute which would flash immediately to vapor and be carried downwind. The estimated distance to toxic endpoint would be 0.1 miles, affecting a very low residential population (< 100 people).
The NPU WWTP has developed and implemented standard operating procedures (SOPs) and policies in order to reduce the li
kelihood of a release of chlorine. SOPs developed to date include:
7 Chlorine Cylinder Handling and Changing Procedures
7 Chlorine Line Blockage Procedures
7 Emergency Procedures
7 Chlorine Storage and Handling Procedures
7 Maintenance Checklists and Procedures
7 Chlorine Procedures for Normal Operations
7 Startup Procedures Following Shutdown
The Chlorination Process has several safeguard features including the use of "Chloromatic" valving and chlorine alarm systems. There was one accidental release of chlorine at the NPU WWTP within the last five years, which occurred in October 1996. Two employees received minor injuries as the result of a release of approximately ten (10) pounds of chlorine. Corrective actions were developed and implemented.
An Integrated Response Plan (IRP) has been developed and implemented by NPU for their water purification and wastewater treatment plants. The IRP provides a systematic approach to facility response for a spectrum of emergency incidents incl
uding medical, fire, explosion, chemical release, and bomb threat. The IRP outlines procedures for notification of internal and external (local and state) responders for all conceivable emergency and non-emergency situations. The NPU has established a chain-of-command system, notification procedures, and alert systems procedures. Exercises and drills are conducted on a regular basis as part of employee training.
NPU programs are developed to accommodate additions and revisions of relevant sections to reflect organizational changes and updates as knowledge on hazard control accumulates. Change is ongoing in most fields of scientific and legislative endeavor. As regulations are promulgated by the Occupational Safety and Health Administration (OSHA), the National Institute of Occupational Safety and Health (NIOSH), the Environmental Protection Agency (EPA), and National Fire Protection Association (NFPA), our programs will be updated.