Marion Municipal Utilities
Risk Management Plan
The City of Marion Wastewater Treatment Facility is a 12.0 MGD conventional activated sludge facility with single stage nitrification, phosphorus removal, and anaerobic digestion.
Disinfection is by chlorination followed by de-chlorination. Specific processes incorporate the use of certain regulated substances. The disinfection process utilizes chlorine, followed by sulfur dioxide addition for de-chlorination. The maximum intended inventory of chlorine is 6,000 lbs. However, there can not be more than 4,000 lbs in use at one time. The maximum intended inventory of sulfur dioxide is 900 lbs. A by-product of anaerobic digestion is the production of methane, and other gases, commonly known as digester gas. Digester gas is collected and stored for use as fuel to power pumps, blowers, and heating systems. The maximum storage capacity for digester gas is 47,710 cubic feet, or 1,891 lbs.
The maximum intended inventory of chlorine exceeds the EPA Threshold Quantity (TQ) of 2,500 lbs. Therefore, the Marion Wastewater Treatment Facility must develop and implement a Risk Management Plan, in compliance with 40 CFR par 68. The inventories of other regulated substances do not exceed the TQs for those substances and are not included as a part of the plan.
Facility personnel will follow routine maintenance procedures in making required repairs, in the event of a minor chlorine leak. If the leak is significant, the City of Marion Fire Department will be contacted to respond, per the facility Emergency Action Plan.
A large leak, developing in a full one ton cylinder stored outside of the chlorination building would be considered a worst case scenario. All of the contents of the cylinder would be released as a toxic gas within the span of approximately ten minutes. There are no passive mitigation measures in this case. Under worst case weather conditions, the chlorine would travel 5.4 miles before dispersing enough to no longer pose a hazard to the public.
The Accident Release Prevention Program is, in effect, the OSHA Process Safety Management Program and the USEPA Risk Management Program.
One of the key safety features of the chlorination process is the piping system. This system operates under a vacuum condition, preventing accidental release of chlorine gas into the atmosphere. If the integrity of the piping system is compromised, the loss of vacuum automatically terminates the release of chlorine gas from the system. A positive pressure piping system, which incorporates pertinent safety devices, is in place as a backup.
The ventilation system is integral to the safety of the chlorination process. This system, which can be operated either automatically or manually, has the inlet vent at floor level because chlorine gas is heavier than air. A chlorine gas detector triggers warning devices and activates the ventilation system, if atmospheric levels of chlorine gas are detected at one part per million or greater.
Personal protective equipment is stored remotely to provide safe access in the event that the atmosphere around the chlorine building becomes contaminated. Emergency repair kits are stored in the chlorine building and are painted bright yellow with clear labeling. These kits are routinely demonstrated in safety training sessions to insure proper knowledge regarding the equipment and its use. The repair devices are properly maintained and replenished as required to insure availability in the event of an emergency.
If the automatic chlorine detection equipment fails, leaks are detected through routine inspection using ammonia. In the presence of chlorine, ammonia produces a white vapor. Chlorine odors can be detected at levels as low as 0.5 mg/l and an audible hissing can be detected in more serious cases.
Training programs are in place, providing instruction regarding the proper use of personal protective equipment as well as procedures for routine maintenance repairs.
If a leak is considered to be minor, a team of at least two trained facility personnel will make the appropriate repairs. All pertinent personal protective equipment will be used as required.
On August 1, 1994 a minor leak resulted in the release of approximately 44 lbs of chlorine gas. This release did not result in any on-site or off-site death, injury, property damage, environmental damage, evacuations, or sheltering in place. This is the only incident involving chlorine release in the past 5 years and does not qualify as a reportable release as defined by 40 CFR 68.42 (a).
The Marion Wastewater Treatment Facility has an Emergency Action Plan, which has been coordinated with the City of Marion Fire Department. In the event of a leak, the plan requires that the individual, having discovered the leak, remove themselves from the effected area and immediately report the condition to his/her supervisor. Each employee is trained to be aware of potentially dangerous conditions.
The supervisor will initiate the alarm for evacuation and will attempt to notify other department supervisors as to the nature of the alarm. The supervisor will then notify the fire department of the emergency condition. Each department supervisor will be responsible to observe the windsock on top of the chlorine storage building and determine the best evacuation route as specified in the Emergency Action Plan. Employees unable to communicate with their supervisor should observe the windsock and follow an evacuation route upwind. Evacuation route maps are posted in several notable areas throughout the facility.
If an alarm sounds during weekday shifts, each employee should stop work activities, shut down equipment, wear clothing appropriate for the weather conditions, and assemble at their supervisor's office. If an employee can not reach the supervisor's office, he/she should observe the windsock and choose an evacuation route upwind.
The Marion Fire Department will be responsible for rescues as required. An employee requiring medical services shall be treated at Marion General Hospital. Both have been notified as to the possibility of an emergency by letter. The local emergency planning committee has been notified of the potential hazards of chlorine. In the worst case scenario, as described above, the Grant County Emergency Management Agency will conduct evacuation efforts.