City of Turlock Waste Water Treatment Facility - Executive Summary
RISK MANAGEMENT PROGRAM |
City of Turlock Water Quality Control Facility
Chlorine Injection System
The City of Turlock Water Quality Control Facility (TWQCF) prepared a chemical risk management program (RMP) in general accordance with California Code of Regulations, Title 19, Section 2735.1, et. Seq. The regulations are also referred to as the California Accidental Release Prevention (CalARP) program. The Federal Environmental Protection Agency (EPA) also regulates facilities with certain toxic and flammable substances. The federal regulations are codified in Title 40 of the Code of Federal Regulations (CFR), part 68.
TWQCF prepared the RMP to satisfy regulatory requirements and to demonstrate a commitment to evaluate and improve chlorine handling systems and practices at the facility. TWQCF has incorporated state-of-the-art safety features into the chlorine system at the facility as part of system modifications and upgrades. In the unlikely event
that a chemical release does occur at the facility, TWQCF personnel are trained in the appropriate response measures, relying on emergency services provided by the local fire department and the Stanislaus County Hazardous Materials Response team. TWQCF will continue to improve chlorine-handling safety through the implementation of the prevention program elements of the RMP.
TWQCF, at 901 South Walnut Avenue in Turlock, California, is located in an area zoned for commercial and industrial use. The facility is near Highway 99, which runs north and south through Turlock. TWQCF processes an average daily flow of 10.2 million gallons per day (MGD) with a design capacity of 20 MGD. Plant influent comes from Turlock's residential, commercial, and industrial customers. As a Regional Treatment facility, TWQCF also teats the wastewater from both Denair and Keyes Community Service Districts.
The major processing units are: 1) primary treatment, which removes settleable solids; 2) secondary
treatment, which removes suspended and dissolved organic solids removed from the waste stream. These unit processes combine to remove approximately 95% of the solids entering the facility. Four anaerobic digesters function to stabilize the solid wastes removed from the primary and secondary systems. After flowing through the various systems, the plant effluent is disinfected with chlorine and dechlorinated with sodium bisulfite, then discharged to the San Joaquin River via an irrigation field.
The RMP regulations require facilities to identify and evaluate chemical release scenarios resulting from potential failures of the chemical handling systems covered by an RMP. Program 3 requirements of the RMP apply to TWQCF due to the quantity of chlorine used. Program 3 facilities are required to evaluate a worst-case release scenario (release parameters are defined by the regulations) and an alternative release scenario. A worst-case release scenario is defined in the regulations as; "
the greatest amount held in a single vesselreleased as a gas over 10 minutes." An alternative release scenario is identified as a release that is more likely to occur at the facility.
The largest chlorine vessels at TWQCF, the one-ton containers, each have a maximum capacity of 2,000 pounds of chlorine. At any given time, there is the potential to have eight full and four full or partially full one-ton containers at the site. TWQCF recently completed modifications to the system, moving the vacuum regulators to the one-ton containers. This modification eliminated the interconnection of the one-ton containers and greatly reduced the amount of chlorine that would be released in the event of a catastrophe. Therefore, the worst-case release scenario for the facility is a release of 2,000 pounds of chlorine in 10 minutes. Catastrophic failure of the chlorine container would be required for this scenario to occur. Assuming pessimistic atmospheric conditions, very conservative chemical
dispersion characteristics, and a toxic endpoint of three parts per million (ppm) chlorine vapor, the predicted distance to the toxic endpoint for the worst-case release scenario is 3.0 miles. The EPA Risk Management Program Guidance for Wastewater Treatment Plants, October 1998, was used for the chemical dispersion analysis. No administrative controls or mitigation measures were considered in the analysis.
An alternative release scenario described in the above referenced EPA guidance document was used by TWQCF. The release scenario is described as a 1/4-inch effective diameter orifice leading to an airborne release, representative of a faulty regulator or valve. The evaluation used a release rate of 150 pounds/minute and average weather conditions. The predicted distance to the toxic endpoint is 0.6 miles.
The RMP regulations require a review of the accidental release prevention program and chemical specific prevention steps used by the facility. TWQCF has incorporated many
safety features in the chlorine system to prevent system failures and to mitigate potential releases. The predominant safety concern with chlorine gas water treatment systems is a release from the pressure side of the system. TWQCF has greatly reduced this risk by moving the vacuum regulators to the ton containers. Any leak in the system, other than from the tank itself, will now be limited to the amount of chlorine in the pipeline. The TWQCF chlorine systems are continuously monitored by automated control systems that regulate the rate of chlorine flow to the chlorinators. Chlorine flow will not occur without the vacuum created by water flowing past the injectors.
In addition to the physical features of the chlorine system at the facility, TWQCF has administrative controls in place to maintain safe operation of the systems. Administrative controls include, but are not limited to: formal training programs for system operators and emergency responders, a hot work permit program,
a lock-out/tag-out program, a line break program, a contractor safety program, and a management of change program. Written standard operating procedures (SOPs) are currently being prepared for the chlorine systems at the facility and will provide a basis for site specific operator training and a ready reference for operating and trouble-shooting the systems.
TWQCF is committed to maintaining the mechanical integrity of the chlorine system. Lead washers are replaced and the flexible connection lines (pigtails) are inspected each time a full tank of chlorine is connected to the system. The pigtails are inspected annually and replaced upon any indication of deterioration. Annual maintenance of the vacuum regulators, chlorinators, injectors, system is performed by Borges & Mohoney, a private chlorine system maintenance contractor. Preventive maintenance at the facility includes shift, daily, weekly, and periodic inspection, calibration, and testing of chlorine system equipment.
RMP regulations require a review of the five-year accident history at the regulated facility. TWQCF reported that they have not experienced an accidental release of chlorine during the past five years.
In the unlikely event that a chlorine release requiring emergency response occurs at the facility, TWQCF has trained all water treatment operators for emergency response. An in-house chlorine safety course, which covers general chlorine safety and handling, flexible pigtail and lead gasket use and replacement, chlorine tank repair kit use and emergency response procedures, is given to all water treatment operators. Self Contained Breathing Apparatus (SCBA), CPR, and first aid training is also provided. TWQCF has a respirator program as prescribed by OSHA's Respiratory Protection Standard. The facility has a written emergency response program that identifies the roles, responsibilities, and actions of the emergency responders. TWQCF will not be relying on local community responders
to mitigate chlorine releases at the facility. TWQCF will rely on community responders for medical assistance and public evacuation or protection in place, if necessary.
Changes to improve safety at the facility are ongoing. Many of the mitigation measures suggested by the process hazard analysis team have already been implemented. Others will be implemented during the next several months. The status of significant mitigation measures is as follows:
7 Installed pressure vacuum regulators on each chlorine cylinder.
7 Motion detector system has been installed and connected into telemetry system.
TWQCF will respond to all suggested mitigation measures. TWQCF is establishing schedules of proposed actions. Management responses and support will be consistent with TWQCF's commitment to safe and environmentally responsible operations.