Manhattan Wells Chlorination Station - Executive Summary
Chlorine is the most commonly used substance for disinfecting drinking water. The addition of chlorine or chlorine compounds to water is called chlorination. Chlorination is considered to be the most important process for preventing the spread of waterborne disease in drinking water. The Los Angeles Department of Water and Power (DWP) also uses chlorine for drinking water disinfection purposes to protect public health per state and federal water quality standards. Storing and handling large quantities of chlorine can create hazardous situations. DWP takes safety obligations in storing and using chlorine as seriously as it takes providing safe drinking water. The DWP Manhattan Wells Chlorination Station chlorine handling process is subject to the U.S. Environmental Protection Agency (EPA) Risk Management Program and Plan and also to the California Accidental Release Prevention (CalARP) Program. These Programs require a summary in the Risk Management Plan (RMP) of policies and pro |
cedures followed to safely operate the facility, including a description of the possible consequences in case of an accident and the actions which will be taken by the facility in an event of an emergency. The following information is specifically required in the RMP Executive Summary:
7 Accidental release prevention and emergency response policies.
7 General facility and regulated substances information.
7 Offsite consequence analysis results.
7 Summary of the accidental release prevention program and chemical-specific prevention steps.
7 Five-year accident history summary.
7 Emergency response program summary.
7 Planned changes to improve safety.
The above information for the Manhattan Wells Chlorination Station is provided below.
Accidental Release Prevention and Emergency Response Policies
The DWP accidental release prevention policy involves a unified approach that integrates the use of proven technology, trains staff in operation and maintenance practices, and uses tested and
proven management system practices. All applicable requirements of the State of California and EPA's Prevention Program are adhered to, including key elements such as training, systems management, and emergency response procedures.
The DWP emergency response policy involves the preparation of emergency response plans for hazardous materials which are tailored to each facility and to the emergency response services available in the community, and is in compliance with the EPA and CalARP Program Emergency Response Program Requirements. The Manhattan Wells Chlorination Station has prepared an Emergency Response Plan for Hazardous Materials to facilitate coordination and emergency planning with offsite response officials and facilities in the event of an emergency. The emergency response plan has been coordinated with local response agencies (City of Los Angeles Fire Department). The Manhattan Wells Chlorination Station has an excellent record in preventing accidents from occurring.
General Facility and Regulated Substance Information
The Manhattan Wells Chlorination Station is located at 6219 Manhattan Place between Gage Avenue and 62nd Street, west of Harbor Freeway and south of Slauson Avenue. It is in the midst of a commercial and industrial area. The station has been installed to disinfect water that is discharged from various wells and is distributed for domestic and industrial consumption in east-central Los Angeles. The station has a building with storage area for chlorine ton containers and a chlorinator room with two chlorinators with injectors. The facility currently stores chlorine, a regulated toxic substance under the EPA and CalARP Program rules. There is a maximum of three chlorine one-ton containers at the chlorination station. A maximum of two one-ton containers can be attached to the chlorine header for discharging chlorine gas at one time. The third container is stored as a spare and is not connected to the process. The one-ton container i
s the largest vessel (container) on line. The maximum quantity of chlorine present at the Manhattan Wells Chlorination Station at any given time exceeds the listed threshold quantities in the EPA and CalARP rules. It also exceeds the listed threshold quantities in the federal and California Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) Standards. However, the facility is normally unmanned and water treatment operators visit the facility daily and respond to any trouble alarms which may occur. Thus, the DWP Manhattan Wells facility is not subject to federal or California OSHA PSM regulations.
There is a maximum of three chlorine one-ton containers at the chlorination station. Two ton containers rest on load cell scales, which allows the operators to monitor the chlorine weight remaining in the container. Chlorine gas is withdrawn from the ton container through a vacuum regulating valve, which is installed directly on the container angle valve.
Chlorine gas is pulled under vacuum from the vacuum regulating valve through plastic tubing and the chlorine header lines to one of the two chlorinators provided at the chlorination station. In case of rupture of the plastic tubing connecting the container to the header lines, air would be drawn in rather than chlorine being released, and the vacuum regulator would shut down the chlorine supply at the container angle valve, operating as a shut-off valve. From the chlorinator, the gas is pulled by vacuum to an injector on the wall where chlorine gas is dissolved into mixing water to form a concentrated solution. This solution is then piped into the pumping station forebay for further mixing to provide disinfection. This chlorinated water is then piped into the water distribution network.
Residual free chlorine is continuously monitored by a residual analyzer. Rate of gas flow through the chlorinator is adjusted by a controller in response to flow and residual signals.
A chlorine lea
k detector has been installed inside the chlorine building, which alarms locally as well as at the DWP's Los Angeles Aqueduct Filtration Plant (LAAFP) at Sylmar.
In the event power is lost at the chlorination facility, an alarm will alert the LAAFP control room. Loss of power will cause the UPS system to take over powering station controls. Chlorine flow will continue unaffected with no safety consequences.
The facility is normally unmanned; water treatment operators visit the facility daily. A response team coordinated from DWP Los Angeles Aqueduct Filtration Plant (LAAFP) responds to any trouble alarms which may occur. Access to the facility is through gates, which are kept locked all the time.
Offsite Consequence Analysis Results
The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst-case release scenario" and "alternative release scenario". The first scenario is defined by EPA, which states that "the owner or operator
shall assume that the ... maximum quantity in the largest vessel ... is released as a gas over 10-minutes," due to an unspecified failure. The alternative scenario is defined as "more likely to occur than the worst-case release scenario".
Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint" selected by EPA of 3 ppm, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as the "maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action." The residential population within a circle with a radius corresponding to the toxic endpoint distance has to be defined, "to estim
ate the population potentially affected".
The worst-case release scenario at the Manhattan Wells Chlorination Station involves a failure of the one-ton container and release of 2,000 pounds of chlorine to the atmosphere over a 10-minute duration, regardless of how improbable this may be. The chlorine release rate to the atmosphere was defined to be 200 lbs./min. No passive mitigation systems were considered in determining the chlorine release rate to the atmosphere.
EPA and CalARP regulations require that the models used for dispersion analysis should appropriately account for the density of the released gas. Since the chlorine cloud formed during the worst-case release scenario would be denser-than-air, the Dense Gas Air Dispersion (DEGADIS 2.1) model was used for performing the air dispersion modeling analysis.
EPA-mandated meteorological conditions, namely Stability F, wind speed of 1.5 m/sec, highest daily maximum temperature (1100F), and average humidity (71%) were used for the
dispersion modeling analysis. The results of the dispersion modeling analysis indicated that the worst-case scenario has offsite impacts.
RMP and CalARP rules require that a scenario which results in offsite toxic endpoint distance and is more likely to occur than the worst-case scenario should be selected as the alternative release scenario, unless no such scenario exists. Unlike the worst-case scenario, the alternative release scenario may consider "active" mitigation such as automatic shutoff valves, excess flow valves, and containment with scrubbers. Active mitigation is defined as requiring mechanical, electrical, or human input.
The alternative release scenarios must consider the facility accident history and/or failure scenarios identified in the hazard review. A review of the past five-year accident history data for the chlorination facility pursuant to these rules indicated that there were no chlorine releases, which could have resulted in offsite (outside the Manhattan
Wells Chlorination Station boundary) toxic endpoint distances. Similarly, no credible accident scenario was identified from the hazard review, which would reach offsite. Thus, an acceptable/credible alternative release scenario had to be selected based on expert judgement.
The scenario selected for the Manhattan Wells chlorination system involves the release of chlorine from the chlorinator relief valve. The one-ton containers are connected to vacuum regulating valves so the chlorine gas flows under vacuum. If the vacuum regulating valve fails to seat properly, the pressure in the container will break the vacuum and the relief valve in the chlorinator will lift, venting chlorine inside the building. The control room would have been warned of the chlorine leak by the chlorine monitors installed at the station. It is assumed that approximately sixty minutes would be required for operators or an emergency response team to respond. The chlorine containers are stored inside an enclo
sed building, which results in a passive mitigation of any release. The release rate reduction from the enclosed building is approximately 55 percent of the release rate from the ton containers, per guidance from EPA regarding control efficiencies for buildings storing chlorine. The amount of chlorine released was estimated at 0.05 lbs, at an average rate over one hour of 0.0008 lb/min.
The alternative release scenario toxic endpoint was also estimated using the Dense Gas Air Dispersion (DEGADIS 2.1) model. The toxic endpoint for chlorine is 3ppm. The results of the dispersion modeling analysis indicated that the alternative release scenario has no offsite impacts. The typical meteorological conditions used were Stability D, wind speed 3.0 m/s, average air temperature of 650F, and 71% average humidity.
Finally, no chlorine releases that could have caused safety or health hazard (no deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at
the Manhattan Wells Chlorination Station during the last five years.
Summary of the Accidental Release Prevention Program and Chemical-Specific Prevention Steps
The DWP accidental release prevention program is based on the following key elements:
7 Detailed management system and clear levels of responsibilities and team member roles.
7 Comprehensive safety information that is readily available to staff, emergency responders, and contractors.
7 Comprehensive preventive maintenance program.
7 Performance of hazard review of equipment and procedures with operation and maintenance staff participation and review.
7 Use of state-of-the-art process and safety equipment.
7 Use of accurate and effective operating procedures, written with the participation of the operators.
7 High level of training of the operators and maintenance staff.
7 Implementation of an incident investigation, inspection, and auditing program using qualified staff.
Chemical-specific prevention steps include availabili
ty of self-contained breathing apparatus (SCBA), worn by the operators during connection/disconnection of chlorine supply, awareness of the hazardous and toxic properties of chlorine, presence of a chlorine detector with remote monitoring, and the use of vacuum regulating valves mounted on the ton containers.
Comprehensive chemical data has been assembled to include regulatory reporting and action thresholds, health hazard, and chemical exposure limitations, as well as detailed physical properties of chlorine. This information includes chlorine background information and MSDS sheets.
Equipment safety information was compiled on the chlorine process. Specifications for the chlorine process are collected and provided in one place for easy reference Details such as maximum intended inventory; safe upper and lower temperatures; and safe upper and lower pressures for the chlorination facility are on file at the facility. DWP also has procedures in place that are trigge
red to update safety information if there is a major change that makes existing information inaccurate.
In 1993, a detailed hazard review was conducted for the chlorination system equipment and procedures. The hazard review was further reviewed in April 1999 and will be updated again within a five-year period or whenever there is major change in the process. A list of recommended actions was developed in April 1999 to further improve the chlorine safety and staff is currently evaluating these recommendations. Staff will document the completion of the recommended actions.
A seismic walkthrough was recently completed based on the 1997 UBC LEPC Region 1 guidance document, and recommendations were provided to DWP staff for their evaluation and implementation.
DWP has prepared written operating procedures for Manhattan Wells chlorination facility that provide clear instructions or steps for safely conducting activities relating to chlorination proce
ss. They are consistent with the chlorine safety information. Written operating procedures included in the facility's Operation and Maintenance Manual for Chlorination Stations include:
7 Delivery of Chemicals
7 Container Connections
7 Normal Operations
7 Shutdown, and
7 Operating Problems and Remedies.
The DWP ensures that each employee operating or maintaining the chlorination process, and each employee newly assigned to this process, is trained and tested for competency in the operating procedures listed above. The DWP employee training documentation files include training records for each employee assigned to operate or maintain the chlorination process. The training ensures that the employee has the required knowledge, skills, and abilities to safely carry out the duties and responsibilities, including chlorine emergency response, as provided in the operating procedures. Employee training includes as a minimum the following elements:
7 Safety In
7 Process Technology and Process Equipment, including safety systems;
7 Maintenance Procedures;
7 Operating Procedures for the chlorine system;
7 RMP Program contents; and
7 Emergency Response Plan and Procedures.
Refresher training is provided at least every three years to each employee operating the chlorination process to ensure that the employee understands and adheres to the current operating procedures. In addition, DWP ensures that operators are trained in any updated or new procedures prior to startup of a process after major modifications.
The DWP operates a Mainsaver Program that generates a task order for performance of the preventive maintenance routine after a designated time past the closing of the previous task order for that maintenance. Description of the work to be performed is included with the printed work order. The water treatment supervisor is responsible for this task.
In addition, the written maintenance procedure is provided in th
e General Operation and Maintenance Manual as follows: Preventive maintenance checklists are provided which summarize inspection, test, and maintenance schedules on a daily, weekly, monthly, biannual, annual, every 2 to 10 years, and as-needed basis. These allow the operator to rapidly review what maintenance is necessary, and provide supervisors with a brief log of maintenance history at the chlorination station. The schedules are supplemental to the log sheets on-site and provide a summary and quick reference to manufacturer's O&M manuals.
DWP documents inspection, testing, and maintenance of chlorination equipment and assures the performance is done in accordance with the recommendations of the manufacturer and industry groups (i.e., Chlorine Institute).
Internal Compliance Audits
The DWP will certify every three years (or earlier) that compliance with Program 2 Prevention Program requirements are met and that procedures and practices developed are adequate and being followed.
The compliance audit will consist of separating the RMP program elements or sections, and auditing each element to determine compliance and effectiveness. For each internal audit, the audit team will complete a Compliance Audit Certification Page and a Compliance Audit Checklist. The Compliance Audit Certification Page provides process identification, the dates of the audit, team members, and certification by the audit leader and the Plant Manager. The Compliance Audit Checklist details the requirements of each RMP element and contains questions that may assist with the auditing process. The audit checklist for each element consists of the following three sections:
7 Records Review: A review of the RMP written Prevention Program.
7 On-Site Conditions: The audit team will review the program elements based on observation of the plant conditions and safety practices.
7 Interviews: The program elements will be evaluated by interviewing personnel from appropriate functions including op
erations, maintenance, management, and contractors.
Team members will record RMP program deficiencies identified during the audit on the checklist.
The DWP incident investigation procedures describe incident reporting, investigation, and investigation reporting steps to be followed by plant personnel. The incident investigation shall be started promptly but no later than 48 hours after the event. The DWP will promptly address and resolve all recommendations and shall implement the recommendations in a timely manner to prevent an incident recurrence. All incident investigation reports will be retained on DWP file for at least a period of five years from the date the reports are completed.
Five-year Accident History Summary
No chlorine releases that could have caused safety or health hazard (deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at the Manhattan Wells Chlorination Station during the last five years.
Emergency Response Program Summary
DWP is a first responder, its employees respond to chlorine accidental releases. Depending on the severity of the accidental release, external resources such as the City of Los Angeles Fire Department may be solicited to aid in handling a chlorine release.
As part of the emergency response program, the DWP has developed and implemented an emergency response plan for the purpose of protecting public health and the environment. The following elements are included:
(a) An emergency response plan, maintained at the stationary source and at the Los Angeles Aqueduct Filtration Plant (LAAFP) containing:
7 Organizational structure (chain-of-command) and responsibilities of various DWP personnel.
7 Procedures for planning and coordination with off-site emergency response organizations.
7 Details of the training programs for all employees involved with the chlorination process, contractor training, and medical surveillance of DWP personnel who respond to
7 Details of emergency recognition and prevention at the DWP.
7 Procedures for informing the public and local emergency response agencies about accidental releases.
7 Documentation of proper first aid and emergency medical treatment necessary to treat accidental human exposures and the detailed information on emergency health care.
7 Procedures and measures for emergency response after an accidental release.
(b) Procedures for the use of emergency response equipment and for its inspection, testing, and maintenance.
(c) Training in relevant procedures for all employees involved with the chlorination process.
(d) Procedures to review and update, as appropriate, the emergency response plan to reflect changes and ensure that employees are informed of changes.
Planned Changes to Improve Safety
As part of the preparation of a Risk Management and Prevention Program (RMPP), a hazard review was performed in 1993 for the chlorination system. The hazard review was performed
using the Hazard and Operability (HAZOP) technique and covered both equipment and procedures used for the chlorine handling system. A number of equipment and procedural changes were made as part of the implementation of the recommended actions. All the above recommendations have been evaluated by the DWP. One of the recommended actions was the replacement of pressurized chlorine gas system with an all-vacuum system. This recommendation has also been evaluated and implemented. Additional 14 changes to further improve chlorine safety were identified in April 1999, when the hazard review was completed for the facility. It is expected that these recommendations will be evaluated by December 1999. The implementation of these recommendations will further improve the safety of the chlorine system.