North River Water Pollution Control Plant - Executive Summary
The North River Water Pollution Control Plant is one of the 14 facilities operated by the New York City Department of Environmental Protection (NYCDEP) which treats the City's wastewater. Each of these facilities produces methane as a byproduct of anaerobic digestion of sewage prior to discharge of the treated effluent into waterways (and dewatering of biosolids [sewage sludge] for beneficial use.) This processing of wastewater is an essential step in preventing the pollution of New York City's surface waters. Digester gas is used in the facility to provide domestic and treatment process heat. It also fuels engines which power equipment.
The methane in the digester gas is a regulated flammable substance under both the EPA and OSHA regulations. At North River the maximum inventory of digester gas exceeds the regulatory threshold of 10,000 pounds.
New York City DEP is committed to protecting its employees, the public, and the environment from any accidental releases of
hazardous materials used at its facilities. We have implemented safety, environmental protection, and risk management programs to prevent hazardous materials releases.
If there is an accidental release, we will immediately call for emergency response to minimize the effect of the release and notify the public of any actions necessary to ensure public protection, through the Fire Department of New York.
Worst-Case Release Scenario
The NYCDEP has conducted an offsite consequence analysis as required by the regulations, including an extremely unlikely, worst-case release scenario (i.e., total release from the single largest container over a ten minute period, assuming worst case meteorological conditions followed by an explosion of the resulting vapor cloud). Results of this worst-case event indicate that offsite receptors would be affected.
A release represented by this worst-case scenario is extremely unlikely because of the robust design of digester vessels and gas holders (th
ey are designed to withstand pressures well in excess of normal operating conditions) and the rigorous maintenance and prevention programs in place at North River.
In fact, EPA release reporting databases and industry experience suggest that the worst-case release scenario as defined in the RMP regulations is so unlikely that it should not be used as the basis for emergency planning. A more reasonable potential release scenario for emergency planning is presented in "The alternative release scenario(s)" section below.
Alternative Release Scenario
A "credible worst-case" scenario, formulated in accordance with USEPA guidance, was selected as the North River alternative release scenario. This scenario involves a ten-minute release of the contents of a vessel followed by a vapor cloud fire. Results of this credible worst-case event indicate that offsite receptors would not be affected.
The results of the process hazard analysis (PHA) and the facility's operating history suggest th
at even this credible worst-case is extremely unlikely to occur, but it can serve as the basis for emergency planning.
Accidental Release Prevention Steps
NYCDEP is committed to personnel safety, public safety, continued reliable operation and regulatory compliance. Based on this commitment, the Plant Chief has assumed overall responsibility for the development and implementation of the Risk Management Program. The Plant Chief has also clearly defined accountability and responsibility for each of the prevention program elements to meet both EPA and OSHA Process Safety Management requirements.
To ensure that a worst-case or alternative release scenario does not occur, the NYCDEP maintains a release prevention program with the primary focus of protecting plant employees and the public from the hazards associated with an accident or release involving methane. The multifaceted program includes the use of:
Flammable gas detectors and alarms to rapidly alert operators to any problems
Process safety information to document the safe process design;
Process hazards analyses to evaluate the chemical and process hazards;
Operating procedures to ensure that the system is operated safely;
Maintenance, inspection and testing to ensure that the system is maintained according to applicable standards and manufacturer's recommendations;
Training, Hot Work Permits, Contractor Safety, and Employee Participation Programs to ensure that all employees and contractors working on and around the processes are aware of the hazards, can perform their job duties safely and know the actions to be taken in an emergency;
Management of Change and Pre-startup Safety Reviews to ensure that changes are documented, analyzed and kept within the design basis;
Incident Investigation procedure to investigate each incident and "near misses" to determine root causes and make needed safety improvements; and,
Periodic Compliance Audits to ensure that our programs are working as they should to
protect both employees and the public.
Five-Year Accident History
Within the past five years, North River has not had any accidental releases that resulted in injuries or property damage. The plant has maintained an excellent safety record throughout its operating history and has never had a major methane release that could have had adverse effects on the public.
In the event that a methane release does occur, North River has an emergency response program that coordinates emergency response with the Fire Department of New York. If such a release did occur, plant personnel would contact the Fire Department of New York who would dispatch firefighters to the facility.
Maintaining A Safe Operation
The NYCDEP continually works to safely manage the hazards of methane to protect employees and the community we serve. The Risk Management Program will be maintained to reduce the risk of accidental releases and each year we will conduct training, review procedures, ma
intain the equipment and follow safe work practices. Periodically, we will audit our program, review our Process Hazard Analysis and coordinate with the community emergency response organization.