Patuxent Water Reclamation Facility - Executive Summary
Risk Management Plan Executive Summary |
Patuxent Water Reclamation Facility
The Anne Arundel County Patuxent Water Reclamation Facility (PWRF) located in Crofton, Maryland is designed to treat up to 6 million gallons per day of domestic wastewater. The PWRF treats wastewater from over 50,000 people in Anne Arundel County. The facility is designed to remove pollutants from wastewater before discharging the reclaimed water into the Little Patuxent River. As part of this treatment system, chlorine and sulfur dioxide are used for disinfection and dechlorination, respectively. Chlorine and sulfur dioxide are stored at the facility in one-ton cylinders. Disinfection and dechlorination are common processes used by many wastewater treatment plants in the United States.
Anne Arundel County Department of Public Works personnel have designed and implemented a Process Safety Management (PSM) program to ensure safe operation of the disinfection and dechlorination processes. As part of the PSM
program, a process hazards analysis has been conducted to evaluate the safety of each of these processes. The minimum amount of chemicals required to meet the facility's discharge permit parameters is stored in an enclosed brick building. Standard operating procedures have been written for the safe handling of chlorine and sulfur dioxide cylinders. Annual training is provided to facility personnel in safe handling and use of chlorine and sulfur dioxide, and a strict preventative maintenance program has been implemented for each process. Monitors are installed in the enclosed chemical building to detect any leaks. If a leak is detected, building ventilation systems shut off automatically preventing any chemical from escaping from the storage building. In the event of a leak, Anne Arundel County Fire Department Hazardous Materials (HAZMAT) unit is contacted and, if necessary, they will slowly and safely mitigate the situation under controlled conditions. No releases of chlorine or
sulfur dioxide have occurred at the facility resulting in any off-site impacts.
During development of this Risk Management Plan, PWRF evaluated scenarios that potentially could result in a release of either chlorine or sulfur dioxide from the facility. One scenario evaluated an uncontrolled release of the entire contents of a one-ton cylinder of chlorine or sulfur dioxide. This release scenario which was approximated by using the Anne Arundel County HAZMAT unit's computerized air dispersion models indicated that an unmitigated "worst-case" release would have off- site impacts.
Measures, including leak detection alarms and automatic ventilation shut off, are installed at the storage building to mitigate a potential leak, so it is highly unlikely that the entire contents of a one-ton cylinder would be released without being safely contained in the storage building. Alternative release scenarios for each process were also conducted to evaluate "more likely" releases from the chlorine
and sulfur dioxide processes. Based on the process hazard analysis conducted at the PWRF, a likely scenario might be a leak of chlorine or sulfur dioxide at the connection on a one-ton cylinder. Modeling conducted by the Anne Arundel County HAZMAT unit indicated that such a release would have some off-site impact.
Building mitigation was not considered in the modeling evaluations of either scenarios, therefore the results overestimate the actual area that would be affected by any potential leak. Coordination between the Anne Arundel County Fire Department HAZMAT unit and the facility personnel enhances and ensures safe facility operation as well as emergency response to any chemical situation. The interagency relationship between the HAZMAT unit and the PWRF personnel has fostered open communication and coordination of emergency response procedures and the safe handling and storage practices for chlorine and sulfur dioxide. In addition, HAZMAT unit personnel were directly involved
in development of this Risk Management Plan for the PWRF, both in conducting release scenario modeling and with providing input to the emergency response program at the facility. Through this cooperative effort and the ongoing process safety management procedures at the facility, Anne Arundel County will continue to operate the Patuxent Water Reclamation Facility in an environmentally safe manner.