Tujunga 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 Tujunga 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 proce |
dures 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 Tujunga 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 prov
en 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 Tujunga 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 Tujunga Wells Chlorination Station has an excellent record in preventing accidents from occurring.
Facility and Regulated Substance Information
The Tujunga Wells Chlorination Facility is located at 8801 Arleta Avenue in Sun Valley, California. The facility is located approximately one-quarter mile east of the Hollywood Freeway (State 170) and immediately south of the Tujunga Wash River. This facility is a groundwater well field and pumping station complex. The facility injects chlorine into a collector pipeline before entering or after leaving a 3-million gallon water contact tank. The station consists of a chlorine storage room, a chlorination room, a chlorine control room, a chemical feed\tool room, and a chlorine scrubber. The facility currently stores chlorine, a regulated toxic substance under the EPA and CalARP Program rules. A maximum of nine one-ton chlorine containers is stored at the Tujunga Wells chlorine building. Six of these containers can be connected to the chlorination process to feed chlorine gas and the other three containers are stored as spares. The one-ton
container is the largest vessel (container) on line. The maximum quantity of chlorine present at the Tujunga 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 Tujunga Wells facility is not subject to federal or California OSHA PSM regulations.
In normal operation, four 1-ton chlorine containers are manifolded in two banks of two containers to supply chlorine. These four containers are equipped with Halogen actuators on the angle valves and will close the valves when a chlorine concentration of 10 ppm is detected in the room. The facility has existing connections, without Halogen actuator
s, for one additional ton container to connect to each of the two banks. These two container connections have automatic shutoff valves in the piping system immediately downstream of the pigtail connections. These six containers rest on load cell scales, which allows the operators to monitor the chlorine weight in the containers. There is also space for the storage of three additional ton chlorine containers, which can be used as spares, but are rarely used.
Chlorine gas is withdrawn from a bank of containers through pigtails which are attached to the ton container gas valves. The chlorine flows under pressure to a chlorine header to the pressure-sensitive automatic switch-over valves. The switch-over valves are triggered by the rise in vacuum pressure in the chlorine feed line between the switch-over valve and the chlorinator. The rise in vacuum occurs when the chlorine container pressure approaches zero, which happens when the container is empty. If this occurs, the switch-over
valve will open the alternate chlorine connection, demanding chlorine gas from the alternate chlorine containers. The chlorine gas then leaves the switch-over valve under vacuum to the chlorinators in the adjacent room. From the chlorinators, the gaseous chlorine then travels under vacuum to three chlorine injectors in an underground vault outside the station. At the injectors, chlorine mixes with a high pressure water supply to form a chlorine solution, which then travels to diffuser tubes located in the pipelines.
Residual chlorine analyzers monitor residual chlorine downstream of the diffusers and provide feedback control for subsequent chlorine dosing.
Multiple chlorine leak detectors have been installed inside the chlorine building, which alarm locally as well as at the DWP Los Angeles Aqueduct Filtration Plant (LAAFP) at Sylmar.
The Tujunga Wells site has also installed a caustic solution scrubber actuated by the chlorine detectors at a chlorine concentration of 3 ppm that ca
n neutralize up to 2,000 lb of chlorine.
The scrubber system is powered by imported electricity or by the backup generator during power outages. All other chlorine alarms, communication systems, mitigation devices, and facility controls have backup power supplies or batteries that would allow them to operate if normal electrical power was interrupted.
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 ve
ssel ... 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 estimate the population potentially affected".
The worst-case rel
ease scenario at the Tujunga 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 (1060F), and average humidity (61%) were used for the dispersion modeling analysis. The results of the dispersion m
odeling 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 Tujunga Wells Chlorination Station boundary) toxic endpoint distances. S
imilarly, 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 Tujunga Wells Chlorination Station chlorination system involves the release of chlorine gas from a crack in one of the pigtails connecting a third container in a bank to the gas header. The third container in each bank is not equipped with the Halogen actuator and a leak in one pigtail will allow the 1-ton containers to leak. It is assumed that the crack developed in < inch diameter pigtail corresponds to a hole of 0.0625-inch (1/16-inch) diameter. The control room would have been warned of the chlorine leak by the chlorine monitors installed at the chlorination facility at a chlorine concentration of 1 ppm. At a concentration of 3 ppm, the scrubber is automatically activated at the facility. At a concentration of 10 ppm, the Halogen actuators
close the angle valves on the containers. It is assumed that approximately 60 minutes would be required for operators or an emergency response team to respond. No passive mitigation systems were considered. Two active mitigation systems considered are the actuation of a chlorine detector and the operation of the scrubber.
The chlorine release rate inside the storage room was estimated at 0.6 lb/min (EPA, 1998b). However, the chlorine release rate to the atmosphere from the scrubber would be only 0.003 lb/min. Based on the chlorine release rate of 0.6 lb/min (EPA, 1998b) and the release duration of 60 minutes, the total quantity of chlorine released inside the storage room was estimated at 36 lb for the alternative release scenario.
EPA's SCREEN 3, a steady state screening model, was used for the selected alternative release scenario. The results obtained using this model are expected to be conservative (higher concentrations). SCREEN3 is a Gaussian dispersion model applicable to
continuous releases of non-reactive, non-dense gases that are emitted from point or area sources (EPA, 1998a). The user may predict a conservative worst-case result based on a pre-selected range of worst-case meteorological combinations or may select individual wind speed and stability categories for analysis. The wind speed and stability class combinations considered in the SCREEN3 model for the alternative analysis is the EPA recommended default combination of wind speed of 3 m/s and atmospheric stability of D. The SCREEN3 model predicts one-hour average concentrations for the modeled pollutants. The toxic endpoint for chlorine is 3ppm. The results of the dispersion modeling analysis indicated that the alternative release scenario has no offsite impacts.
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 Tujunga 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 availability 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 chlorine detectors with remote monitoring, use of Halogen actuators on ton containers, and a chlorine scrubber.
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 triggered to update safety information if there is a maj
or change that makes existing information inaccurate.
In 1990, 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 Tujunga Wells chlorination facility that provide clear instructions or steps for safely conducting activities relating to chlorination process. They are consistent with the chlorine safety inf
ormation. 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 Information;
7 Process Technology and Process Equipmen
t, 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 the General Operation and Maintenance Manual as follow
s: 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 operations, 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 Tujunga Wells Chlorination Station during the last five years.
Emergency Response Program Summary
DWP is a first res
ponder, 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 chlorine releases.
7 Details of emergency recognition a
nd 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 1990 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. In addition, Halogen actuators tied into the chlorine detectors have been added to four of the ton containers. Additional 16 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