Joint Water Pollution Control Plant - Executive Summary
Chlorine is the most commonly used chemical for disinfecting wastewater. The County Sanitation Districts of Los Angeles County (CSDLAC) Joint Water Pollution Control Plant (JWPCP) uses chlorine for disinfecting wastewater to provide safe effluent discharges to the environment. Digester gas, on the other hand, is one of the by-products of the sludge digestion process at wastewater treatment plants. Digester gas is used as an energy resource at JWPCP, instead of flaring it as a waste gas as would be done at a number of wastewater treatment plants. JWPCP's chlorine and digester gas processes are 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 procedures followed to safely operate the facility, including a description of the possible consequences in case of an accident and the actions wh |
ich will be taken by the facility in the event of an emergency. The following information is specifically required in the RMP Executive Summary:
* Accidental release prevention and emergency response policies.
* General facility and regulated substances information.
* Offsite consequence analysis results.
* Summary of the accidental release prevention program and chemical-specific prevention steps.
* Five-year accident history summary.
* Emergency response program summary.
* Planned changes to improve safety.
The above information for the JWPCP Chlorine and Digester Gas Systems are provided below.
Accidental Release Prevention and Emergency Response Policies
The JWPCP accidental release prevention policy involves a unified approach that integrates proven technology, staff training in operation and maintenance practices, and tested and proven management system practices. All applicable procedures of the State of California and EPA's Prevention Program are adhered to, includ
ing key elements such as training, systems management, and emergency action procedures.
The JWPCP Emergency Action Plan (EAP) details the procedures to be followed by employees in the event of chlorine or digester gas releases. The EAP also provides information on escape procedures and emergency escape route assignments. JWPCP EAP was prepared for the chlorine and digester gas systems to facilitate coordination and emergency planning with offsite response officials and facilities in the event of an emergency.
General Facility and Regulated Substance Information
The Joint Water Pollution Control Plant treatment facilities are located on a land area of approximately 215 acres within the City of Carson. The property is bounded by the Harbor (110) Freeway on the west, Sepulveda Boulevard on the North, Main Street on the east and Lomita Boulevard on the south. The County Sanitation Districts of Los Angeles County has operated the JWPCP facility since 1928. The JWPCP serves a popu
lation of about 3.5 million people and many industries in southern and eastern Los Angeles County, providing advanced primary and partial secondary treatment for 385 million gallons of wastewater per day.
The purpose of the chlorine system is to provide disinfection to the primary and secondary effluent. The disinfecting medium is calcium hypochlorite, obtained by on-line reaction of chlorine with a lime slurry. The chlorine system consists of the railcar chlorination system, chlorine containment and treatment system, auxiliary systems, including instrument air, pad air, chlorine leak detection, caustic absorption, and a caustic scrubber. Liquid chlorine is delivered to the chlorine station by railcars. Six double walled and insulated tank cars of 90 ton chlorine capacity are usually present on two rail spurs with two cars piped and one actually delivering chlorine.
Dry compressed air is supplied to the railcar being unloaded at 175 psig to provide pressure to move the chlorine
while keeping it in a liquid state. A flexible monel hose connects the railcar to a 3-foot deep pipe gallery located directly underneath the three unloading stations. Three expansion vessels are provided; they protect the liquid chlorine piping from rupture due to pressure buildup from liquid chlorine being trapped between two closed valves and absorbing ambient heat.
Chlorine flows in the pipe gallery to the Injection Room, where liquid chlorine and lime slurry are injected into a process line with water acting as a transport medium. Two chlorine sensors in this room provide leak detection, warning and scrubber activation. An automatic caustic scrubber system provides containment and neutralization of possible chlorine releases in the Injection Room by sealing off external ventilation and recirculating the chlorine-contaminated air through a caustic scrubbing tank and venturi.
In case of a major chlorine leak, the chlorine railcar can be isolated by emergency shutoff valves lo
cated on the piping downstream of the railcar manway. There are emergency shutdown switches (push buttons) located at the unloading rack and at chlorine control rooms. The emergency shutdown switches are also activated by the plant computer control system.
A full containment building and caustic scrubber system able to neutralize the release of 90 tons (one railcar load) of chlorine is provided at the chlorination facility. Upon detection of chlorine gas by chlorine detectors, the scrubber system is activated; chlorine leaking into the containment building is ducted into a venturi scrubber, and neutralized with recirculating caustic solution. The system is capable of neutralizing the contents of a 90 ton chlorine railcar. The scrubber system is of once-through design, the maximum discharge chlorine concentrations from the scrubber stack would be 5 parts per million by volume (ppmv).
Gas analyzers are used to sense a chlorine gas leak in the railcar storage room. Upon detection
of 5 ppm chlorine leak, the following process is initiated: a) the normal ventilation system is shut down in the leak area to contain the gas within the room, b) local visual and audible alarms are actuated, c) remote alarms at the distributed control system operator interface unit located in the control room and the scrubber control panel are activated, and d) the selected duty caustic recirculation pump is started. If the selected duty recirculation pump fails to start, the standby recirculation pump starts automatically and an alarm is annunciated at the control panel. A chlorine analyzer is also used to determine the chlorine concentration in the scrubber exhaust. The scrubber system is also equipped with an emergency generator set. The emergency generator will automatically start after the loss of regular power and will continue to run for 5 minutes after regular power is stored. The emergency generator powers the Containment Building and Injection Room scrubbing systems incl
uding local alarms, the scrubber fan, recirculation pumps, electrically operated valves, and the Bailey.
The purpose of the digester gas system is to use the digester gas produced at the JWPCP as an energy resource, instead of flaring it as a waste gas. The sludge collected from the primary and secondary settling tanks is pumped into sealed digesters and heated, by steam, to approximately 96 deg F to encourage growth of mesophilic anaerobic bacteria. The bacteria consumes as well as stabilizes the sludge and in the process produces digester gas that is approximately 65 percent methane and 35 percent carbon dioxide. The digester gas collects in the head space of the digester and flows via pipelines to one of the following pieces of equipment for combustion: (1) Gas Turbines, (2) Boilers, (3) IC Engines, and (4) Flares.
The digester gas system consists of 24 rectangular and 17 circular anaerobic digesters, gas distribution system, compressors, and flares. Each rectangular digester
has a volume of 100,000 cubic feet and is 57 ft wide, 100 ft long, and has a depth of 18 ft. Each circular digester has a volume of approximately 500,000 cubic ft and is 125 ft in diameter with an average depth of 36 ft. Both the circular and rectangular digesters are identical in process, operation, and control strategy.
Access to the JWPCP facility is through gates, which are closed after regular hours.
Offsite Consequence Analysis Results
The offsite consequence analysis includes consideration of two 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 and vaporizes resulting in a vapor cloud explosion," due to an unspecified failure. The alternative scenario is defined as "more likely to occur than the worst-case release scenario".
RMP and CalARP regula
tions for Program 3 processes require the performance of a consequence analysis for one worst-case release scenario that is estimated to create the greatest distance in any direction to a toxic endpoint resulting from an accidental release of regulated toxic substances from covered processes. For the worst-case release scenario analysis for the JWPCP, one scenario was considered. Only passive or administrative controls are allowed under this scenario to reduce offsite impacts. The scenario used for JWPCP is the rupture of a 90-ton railcar, resulting in a release of 180,000 pounds of chlorine over a 10-minute duration. The release rate for chlorine was thus estimated to be 18,000 pounds per minute inside the building. The chlorine railcars are in an enclosed building, which results in a passive mitigation of any chlorine release. The release rate reduction from the enclosed building is estimated to be approximately 87% of the release rate from the railcar, per guidance from EPA rega
rding control efficiencies levels for buildings storing chlorine. The release rate for chlorine was thus estimated to be 2,304 pounds per minute.
The released liquid chlorine is assumed to form a denser-than-air cloud and then disperse in the atmosphere. The distance to the toxic endpoint was estimated using the EPA's Dense Gas Air Dispersion (DEGADIS 2.1) Model. The toxic endpoint selected by EPA and CalARP rules for chlorine is 3 ppm, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). The toxic endpoint was conservatively set by EPA to ensure public notification and that local emergency response planning takes into account the greatest possible impacted area surrounding the release point. In practice, this type of a total failure of bulk storage tanks would be unlikely. EPA-mandated meteorological conditions, namely atmospheric Stability Class F, wind speed of 1.5 meter per second, highest daily maximum temperature (111 deg F), and average relative humidity (
66%) were used for the worst-case release scenario analysis. The results of the air dispersion modeling indicate that this scenario will result in 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 process hazard analysis. A review of the past five-year accident history data for the chlorination facility pursuant to these rules indicated that there were no such chlorine releases, which could have re
sulted in offsite (outside the JWPCP boundary) toxic endpoint distances. Similarly, no credible accident scenario was identified from the process hazard analysis, which would reach offsite. Thus, an acceptable/credible alternative release scenario had to be selected based on expert judgement.
Since chlorine is the only regulated toxic substance used at the facility, only one alternative scenario was selected for the offsite consequence analysis.
The scenario selected for the JWPCP chlorination facility involves the release of chlorine from the monel flexible hose connecting the railcar to the processes. This scenario can occur if the operator uses a flex hose, which is worn or has a defect, which results in a crack in the flex hose during the withdrawal of chlorine from the railcar. It is assumed that the crack developed in the flex hose (1-inch diameter) corresponds to a hole of 0.1875-inch (3/16 inch) diameter. The control room would have been warned of the chlorine leak by
the chlorine detectors installed at the chlorination facility. It is assumed that a maximum of sixty minutes would be required for operators or an emergency response team to respond and activate the remote controlled shutoff valves installed on the flex hoses after an assessment. Alternatively the leak could be stopped by closing the shutoff valves remotely and placing the standby railcar into service. This would provide indirect evidence that the leak could be stopped by the valves. Personnel would still be required to investigate and determine the source of the leak. The alternative release scenario assumes that this was not done.
The chlorine release rate inside the storage room was estimated at 87 lb./min. However, the chlorine release rate to the atmosphere from the scrubber would be only 0.01 lb/min. Since the chlorine release from the scrubber stacks would be neutrally buoyant, EPA's SCREEN3 model was used for the air dispersion analysis. The meteorological conditions u
sed for the alternative release scenario analysis were Stability D, wind speed of 3.0 meters per second, average air temperature of 61 deg F, and average humidity of 66%. The results of the dispersion modeling analysis indicated that the maximum ground level one hour average concentration for chlorine would be less than 0.1 ppm (0.02 ppm). This concentrations is significantly lower than 3 ppm, the toxic endpoint , and will have no offsite impacts.
It may be noted that the occurrence of this scenario is highly unlikely because the flex hoses are carefully inspected during each connection/disconnection operation, and during operator rounds.
Digester Gas System
RMP and CalARP regulations for Program 3 processes require the performance of a consequence analysis for one worst-case release scenario that is estimated to create the greatest distance in any direction to a flammable endpoint resulting from an accidental release of regulated flammable substances from covered processes. For t
he worst-case release scenario analysis for the JWPCP digester gas system, two scenarios were considered: (1) vapor cloud explosion of the entire contents of a circular digester and (2) the vapor cloud explosion of the entire contents of a rectangular digester. The mass of methane in the digester was estimated as 1,458 lbs and 978 lbs for the circular and rectangular digesters, respectively.
The released methane is assumed to form a gas cloud, which detonates, resulting in a gas vapor cloud explosion. A yield factor of 10 percent of the available energy released in the explosion was used to determine the distance to the explosion endpoint. The distance to the toxic endpoint was estimated using the EPA's guidance. The flammable endpoint specified by EPA is an overpressure of 1 pound per square inch (psi). This represents the threshold for potential injuries to people as a result of property damage caused by an explosion (i.e. injuries from flying glass from shattered windows or fa
lling debris from damaged houses). The results of the offsite consequence analysis indicates that the flammable endpoint circle for the circular digester would not extend to any public receptor. However, the flammable endpoint circle from the rectangular digester would extend offsite and impact public receptors.
As a worst-case alternative release scenario, the complete release of digester gas from a single rectangular digester was selected as an alternative scenario for the digester gas system. It was assumed that the methane released will form a vapor cloud (with all the mass of methane in the flammable range) and a detonation would occur. A yield factor of 3 percent for the TNT-equivalency model (in comparison to 10 percent selected for the worst-case release scenario) was used to determine the distance to the endpoint of 1 psi.
No passive or active mitigation systems were considered for the off-site consequence analysis. However, there is a wall surrounding the digesters tha
t will act as a passive mitigation device and will serve to decrease the explosion (overpressure) impacts. The actual distance to the explosion endpoint overpressure of 1 psi would be smaller than that predicted without considering the mitigation effect of the wall.
The distance to the flammable endpoint was estimated using EPA's guidance. The results of the consequence analysis indicated that the overpressure of 1 psi would extend off-site but would not impact any public receptors.
Finally, no digester gas (methane) releases that could have caused safety or health hazard (no deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at the JWPCP during the last five years.
Summary of the Accidental Release Prevention Program and Chemical-Specific Prevention Steps
JWPCP is in compliance with Federal and State Process Safety Management requirements. JWPCP accidental release prevention program is based on the following key elements:
management system and clear levels of responsibilities and team member roles.
* Comprehensive process safety information that is readily available to staff, emergency responders, and contractors.
* Comprehensive preventive maintenance program.
* Performance of process hazard analysis of equipment and procedures with operation and maintenance staff participation and review.
* Use of state-of-the-art process and safety equipment.
* Use of accurate and effective operating procedures, written with the participation of the operators.
* High level of training of the operators and maintenance staff.
* Implementation of an incident investigation, inspection, and auditing program using qualified staff.
Chemical-specific prevention steps for the chlorine and digester gas systems include the following: availability of self-contained breathing apparatus (SCBA) and/or air purifying respirators worn by the operators during connection/disconnection of chlorine supply, personal protective equi
pment, awareness of the hazardous properties of chlorine and digester gas, presence of chlorine and methane detectors/alarms, and chlorine scrubber.
Process and Chemical Safety Information
Comprehensive chemical data have been assembled to include regulatory reporting and action thresholds, health hazard, and chemical exposure limitations, as well as detailed physical properties of chlorine and digester gas. This information includes chlorine and digester gas background information and MSDS sheets.
CSDLAC also has procedures in place to update process safety information for JWPCP if there is a major change that makes existing information inaccurate.
Process Hazard Analysis
In 1995, a detailed process hazard analysis (PHA) was conducted for the chlorination system equipment and procedures. In 1999, the PHA for the chlorination system was further reviewed. A PHA for the digester gas system equipment and procedures was performed in 1999. Both PHAs for the chlorine and digester
gas processes will be updated again within a five-year period or whenever there is a major change in the process. No recommendations were made to further improve the chlorination system since the process has not been modified. However, a list of recommended actions were developed to improve the digester gas system safety and staff is currently evaluating these recommendations. Staff will document the completion of recommended actions.
A seismic walkthrough was recently completed based on the LEPC 1998 guidance document, and recommendations were provided to JWPCP staff for their evaluation and implementation.
JWPCP maintains written operating procedures that provide clear instructions for chlorine and digester gas processes. The JWPCP ensures effective operating practices by combining them with operating and maintenance training programs. The chlorine and digester gas operating procedures include initial startup, shutdown, and abnormal (temporary) and emerg
ency procedures. Similar procedures for the waste gas flare, compressors, and gas turbine power generation system are also available.
JWPCP updates procedures whenever a significant change occurs in the process or equipment.
JWPCP employees presently involved in operating or maintaining the chlorine and digester gas processes are trained in an overview of the process and applicable operating and maintenance procedures. JWPCP ensures that each employee newly assigned to the chlorine and digester gas processes, is trained and tested to be competent in the operating procedures listed pertaining to their duties. Each employee (presently involved in operating the chlorine or digester gas process) has been trained to receive the required knowledge, skills, and abilities to safely carry out the duties and responsibilities, including emergency response.
Training is currently provided annually to each employee operating the chlorine facility and at a minimum every three years
for operators at digester gas facilities. In addition, the JWPCP ensures that operators are trained in any updated or new procedures prior to startup of a process after a major change as indicated in their Management of Change procedures.
Contractors are properly informed of the hazards, access limitations to the process area, and emergency response procedures. The contractors are informed, prior to the initiation of the work at the site, of the applicable provisions of the emergency response plan. CSDLAC Field Engineering and Environmental Health and Safety Section holds contractor safety briefings before allowing them near or in the process areas, controls access to the process areas, and evaluate the contractor's performance.
Pre-Startup Safety Review and Mechanical Integrity Program
JWPCP ensures that a pre-startup safety review is completed for any new covered-by-the-rules process, or for significant modifications to an existing covered process that requires a
change in the process safety information. JWPCP maintains the mechanical integrity of process equipment to help prevent equipment failures that could endanger workers, the public, or the environment. JWPCP's mechanical integrity program includes the following:
* Written procedures for maintaining mechanical integrity through inspection and testing of process equipment, based on instructions of equipment vendors, industry codes, and prior operating experience.
* Implementation of the written procedures by performing inspections and tests on process equipment at specified intervals.
* Training of maintenance personnel in preventive maintenance program procedures; safe work practices such as lockout/tagout, line or equipment opening, and avoidance and correction of unsafe conditions; and safe use and application of special equipment and/or unique tools.
Hot Work Permits and Management of Change
JWPCP requires employees and contractors to employ safe work practices when performing
"hot work" in, on, or around the covered process. JWPCP uses a permitting program to ensure hot work is conducted safely on or near a process involving chlorine and digester gas.
JWPCP provides a system and approach to maintain and implement any management of change or modifications to equipment, procedures, chemicals, and processing conditions. This system allows JWPCP staff to identify and review safety hazards or provide additional safety, process, or chemical information to existing data before the proposed change would either compromise system safety or need training to be completed.
Internal Compliance Audits
Internal compliance audits will be conducted every 3 years to verify compliance with the programs and procedures contained in the RMP. The JWPCP will assemble an audit team that will include personnel knowledgeable in the Risk Management Program rule and in the process. This team will evaluate whether the prevention program satisfies the requirements of the Risk Manag
ement Program rule and whether the prevention program is sufficient to help ensure safe operation of the process. The results of the audit will be documented, recommendations resolved, and appropriate enhancements to the prevention program will be implemented.
JWPCP investigates all incidents that could reasonably have resulted in a catastrophic release (serious injury to personnel, the public, or the environment) so that similar incidents can be prevented. An investigation team is assembled and the investigation is initiated within 48 hours of the incident. The results of the investigation are documented, recommendations are resolved, and appropriate process enhancements are implemented. Information found during the investigation is reviewed by affected staff and added or used to revise operating and maintenance procedures.
Five-year Accident History Summary
JWPCP chlorination facility had one accidental release of chlorine in the last five years; the re
lease quantity was estimated at one (1) pound. The release caused one on-site injury where the exposed worker was sent to a clinic and referred to a hospital. The worker returned to work after three days. There were no off-site impacts from the chlorine release. A new chlorine alarm and other modifications were made to prevent a similar incident from reoccurring.
Emergency Response Program Summary
JWPCP trained operators are first responders to chlorine and digester gas leak alarms and accidental releases. Depending on the severity of the accidental release, external resources such as the Los Angeles County Fire Department may be called to aid in handling chlorine and digester gas release. As part of the emergency response program, the JWPCP has developed and implemented an Emergency Action Plan for the purpose of protecting the employees as well as the public and the environment.
Planned Changes to Improve Safety
Based on the 1999 PHA, no additional changes were recommended
for the chlorination system. However, for the digester gas system, 6 changes to further improve the digester gas system safety were identified. It is expected that these recommended actions will be evaluated by December 1999. Recommended actions that are determined by evaluation to enhance safety of the covered processes without other negative impacts will be implemented.