Lynchburg Wastewater Treatment Plant - Executive Summary
Chlorine has been widely used to provide effective disinfection and for other uses at wastewater treatment plants. The use of chlorine is not risk free, however. Historically, it is clear that utilities have recognized the risks and have been successful in developing procedures to handle chlorine safely and to protect the off-site public and the environment from potential accidental releases.
As an added layer of protection, the United States Environmental Protection Agency (EPA) promulgated Hazardous Chemical Risk Management Program regulations to further ensure that facility owners understand the risks and take proactive efforts to reduce risk through comprehensive training programs, procedures, and risk mitigation measures. Additionally, EPA wanted the public to be informed regarding these issues.
The Lynchburg Wastewater Treatment Plant has always understood these risks and has maintained a well-trained staff and a safely operated and maintained facility. The tr
ack record of the City of Lynchburg is exemplary with respect to handling hazardous chemicals. Furthermore, the City of Lynchburg has taken a comprehensive approach to be in full compliance with the RMP regulation by June 21, 1999.
The City of Lynchburg owns and operates the Lynchburg Wastewater Treatment Plant (WWTP). The facility's mission is to protect public health and water quality by providing a wastewater effluent free of harmful pathogens for discharge to the James River. Approximately 500 to 1,000 pounds per day of chlorine gas is used to disinfect the wastewater effluent prior to discharge. A maximum of 34,000 pounds of chlorine are stored on-site. The chlorine is stored as a gas that is liquefied under pressure in containers that contain 2,000 pounds each.
Chlorine Process and Safety Equipment
The chlorine system at the Lynchburg WWTP is a liquid system from the ton-containers to the evaporators and a positive pressure gas system from the evapor
ators to the vacuum regulators in the Chlorinator Room. Chlorine is withdrawn from the ton-containers as a liquid and conveyed under pressure to two evaporators in the Chlorinator Room. From each evaporator, chlorine gas is conveyed under pressure to a vacuum regulator located between the evaporator and the chlorinators. Three chlorinators and three injectors are provided. As the pressurized gas from the evaporators passes through the vacuum regulators, it is reduced to a vacuum. The vacuum created by the injectors conveys the chlorine gas from the vacuum regulators to the chlorinators and from the chlorinators to the injectors. At the injectors, the chlorine gas is mixed with water to make the chlorine solution, which is conveyed to one or more of the following application points: raw wastewater, secondary effluent, gravity sludge thickener, and return activated sludge.
Safety equipment for the chlorine system includes exhaust fans and louvers for room ventilation, chlorine det
ectors with local visual and audible alarms, emergency showers and eyewashes, an emergency "B" kit, ten-minute air packs, and a windsock.
Risk Management and Process Safety Management Program Overview
Chlorine is subject to the Environmental Protection Agency's (EPA's) Risk Management Program (RMP) regulation, which can be found in 40 CFR 68, and the Occupational Safety and Health Administration's (OSHA's) Process Safety Management Program (PSMP) regulation, which can be found in 29 CFR 1910.119.
The primary components of the RMP are as follows:
' A five-year accident history
' An off-site consequence analysis for a worst-case and alternative release scenario
' A comprehensive prevention program to minimize risks (i.e., minimize the potential for a release)
' An emergency response program to ensure that an accidental release is appropriately handled
' An overall management program to supervise the implementation of the RMP
Following development of the RMP, the facility must submit
a Risk Management Plan (Plan) to the EPA by June 21, 1999. The Plan is a summary of the facility's Risk Management Program. The RMP will be updated every five years, or whenever a process changes or a new process is added. The OSHA PSM regulation has basically the same requirements as the prevention program element of the EPA RMP. The Lynchburg WWTP RMP meets the requirements of both regulations.
The following sections briefly summarize the elements of the Lynchburg WWTP RMP.
Five-Year Accident History
The Lynchburg WWTP has used chlorine to disinfect wastewater for over forty years. In the last five years, the facility has had no accidental releases which are required to be reported under the RMP regulation.
Off-Site Consequence Analysis
An off-site consequence analysis was conducted for worst case and alternative case release scenarios. The worst case release scenario for chlorine has been defined by the EPA to be an accidental release in which the largest on-site vesse
l releases its contents as a gas over ten minutes. Since the largest container stored at the facility holds 2,000 pounds of chlorine, the worst case release scenario is a release of 2,000 pounds of chlorine over 10 minutes. The alternative release is a "more likely" incident than the worst case. The RMP regulation allows the owner to define the alternative release scenario based on historical experience or operations staff knowledge of their system. The alternative release scenario for the facility was assumed to consist of a pigtail disconnecting from the ton container valve. These two scenarios were modeled to estimate the distance to an endpoint of 3 ppm. It should be noted that this concentration has been found to typically cause minor eye and nose irritation. Since the chlorine ton containers are in an enclosed building, the building provides passive mitigation to reduce the rate of chlorine release to the atmosphere.
The results of the analysis showed that the risk of ch
lorine exposure for the Lynchburg WWTP is relatively low because of site topography and the location of populated areas generally uphill from the treatment plant site. Since chlorine gas is heavier than air, a chlorine release would tend to flow downhill toward low-lying areas. For the Lynchburg WWTP, this would be to the north to the James River, where the chlorine would remain in or around the water until dissipated.
There are always risks associated with handling and using chlorine. These risks include the potential inhalation of chlorine gas if it is accidentally released. The prevention program is a key component of reducing the risk associated with a potential chlorine gas release. Key elements of the prevention program include:
' Employee participation
' Process safety information
' Process hazard analysis
' Incident investigation
' Standard operating procedures
' Mechanical integrity
' Management of change
' Pre-startup review
' Compliance audits
' Hot work permits
' Trade secrets
The following briefly describes the benefits of the following prevention program elements: standard operating procedures, mechanical integrity program, employee training and the process hazard analysis.
The facility staff has developed up-to-date and accurate written standard operating procedures (SOPs) to ensure that operators have clear instructions for safe operation of the chlorine system. Effective SOPs, when combined with operator training, are instrumental in ensuring safe operation of the system and in preventing accidental releases.
The purpose of the mechanical integrity program is to ensure the continued integrity of the process equipment. An effective mechanical integrity program is needed to prevent accidental chlorine releases that may result from mechanical failure of improperly maintained equipment. The Lynchburg WWTP mechanical integrity program includes maintenance, inspection, and testing procedures and s
Knowledgeable well-trained personnel are essential to preventing and mitigating the effects of accidental chemical releases. The Lynchburg WWTP training program ensures that personnel working on or near the chlorine system are adequately trained in operation and maintenance procedures and the appropriate response actions to an accidental chlorine release.
The process hazard analysis is a valuable risk reduction tool that outlines deficiencies in equipment and procedures, identifies potential system failure modes, and provides recommendations for system and operational improvements.
Emergency Response Program
A comprehensive emergency response program has been prepared which outlines the procedures and lines of communication that are necessary to effectively respond to and mitigate a potential chlorine gas release.
In the event of a chlorine gas release in the Chlorine Storage or Chlorinator Room, a detector will detect the presence of chlorine gas. The detector will act
ivate audible and visual alarms to give warning to plant staff. The facility emergency response program includes procedures for notifying the local hazardous materials (hazmat) teams of the incident and procedures for evacuating the facility. Currently, the Virginia Area 8 regional hazmat team in Roanoke will respond to mitigate a chlorine leak. The City of Lynchburg Fire Department has received grant funding and is currently developing a hazmat team. In the future, it is expected that hazmat response will be from the City Fire Department.
Planned Changes to Improve Safety
The City of Lynchburg is currently evaluating additional modifications to supplement existing safeguards for the chlorine system at the Lynchburg WWTP. These include installation of a chlorine monitor to provide local and remote indication of chlorine concentration, and addition of remote alarms for the chlorine detectors. Evaluation of alternative disinfection systems or the addition of emergency chlorine
scrubbers is also planned in the near future. Modification of the chlorine system to provide remote emergency shutoffs on the ton containers is also planned for installation in the near future.