Hyperion Treatment Plant - Executive Summary |
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Introduction The Hyperion Treatment Plant treats municipal wastewater from the City of Los Angeles so that the environmental impact from the City to Santa Monica can be dramatically reduced. Digester gas is a byproduct that is generated when the solids extracted from the wastewater are stabilized in a biological treatment process. Hyperion Treatment Plant sends this gas to Scattergood Power Plant to use as fuel in their power generators. Storing large quantities of digester gas can be a hazard. As the agency responsible for operating Hyperion Treatment Plant, the City of Los Angeles Bureau of Sanitation takes our safety obligations in storing and using these chemicals as seriously as we take in providing the environment with safe treated water. The following document describes what could happen if there were to be an accident, the steps we take every day to ensure safety, and what to do in event of an emergency. Accidental Release Prevention and Emergency Response Policies The City of Los Angeles Bureau of Sanitation and Hyperion Treatment Plant accidental release prevention program involves a unified approach that integrates proven technology, staff training on operation and maintenance practices, and tested management system practices. All applicable procedures of the State of California and U.S. Environmental Protection Agency (EPA) Prevention Program are adhered to, including key elements such as training, systems management, and emergency response procedures. This document complies with the EPA Risk Management Program under Section 112 (r) of the Clean Air Act (CAA) Amendments of 1990, 40 Code of Federal Regulations (CFR) Part 68, and the California Accidental Release Prevention (CalARP) Program under California Code of Regulations (CCR) Title 19, Division 2, Chapter 4.5. The Hyperion Treatment Plant has a system that generates, stores, conveys, and burns digester gas. This document summarizes our existing health and safety programs; our internal m anagement response team, policies, and procedures; and ongoing actions that are designed to prevent or minimize impacts of accidental releases of digester gas to the environment. The Hyperion Treatment Plant has prepared an emergency action plan to handle any potential accidental releases. To date, we have an excellent record in preventing accidents from occurring. General Facility and Regulated Substances Information The Hyperion Treatment Plant, operating since 1946, is located at 12000 Vista del Mar, Playa del Rey, Los Angeles County, California. The plant, located on a 135-acre property, is adjacent to LAX airport at the intersection of Imperial Highway and Vista Del Mar. Wastewater from the Los Angeles Bureau of Sanitation service area is treated at the Hyperion Treatment Plant and discharged into two outfalls, one 3 miles and one 5 miles into the ocean. The wastewater treatment at Hyperion Treatment Plant includes preliminary treatment, flow equalization, primary and secon dary treatment, and coagulation and microfiltration before final discharge. The Hyperion Treatment Plant is capable of handling wastewater flows up to 450 million gallons per day (mgd), with an average flow of 370 mgd. The facility currently generates and stores digester gas (containing 64 percent methane), a flammable regulated substance under RMP and CalARP. Digester gas is stored in 38 digesters, a low-pressure gas holder, and in the plant pipelines. The digester gas process contains approximately 107,000 pounds of digester gas including approximately 43,000 pounds of methane. (The quantity of methane in Section 1.17c.3 of RMP*Submit is reported as digester gas because digester gas is used for applicability determinations). This digester gas storage exceeds the listed threshold quantities in the RMP and CalARP rules. The digester gas process at the Hyperion Treatment Plant is categorized as a Program 1 process under the CalARP regulation. Digester Gas Safety Systems Fire P rotection System Digester systems are provided with a separate, automatic wet-pipe fire extinguishing system with overhead sprinklers. Smoke detectors, heat detectors, and manual pull stations are located throughout the facility and linked to a fire alarm control panel (FACP). In the event of a fire, the system operates automatically by setting off audible and visual alarms, initiating the pre-action fire water sprinkler system, shutting down the interlocked fans and air conditioning units, and releasing any electromagnetically held doors installed in the area. Leak Detection System A combustible gas detection system is installed throughout the digester tunnel complex to sense levels of methane gas. Methane levels are registered on digital displays located in the various control rooms as a percentage of the lower explosive limit (LEL). If levels of methane exceed 10 percent LEL, local alarm horns and flashing warning lights will be activated within the area. Because methane is li ghter than air, the sensors are installed near the ceiling of the tunnels. Methane levels above 10 percent LEL are considered unsafe and requires that all personnel evacuate the area immediately. Pressure Relief Valves Two pressure/vacuum relief valves are provided on the domes of the digesters installed in 1998 and three are provided on original digesters. Each pressure/vacuum relief valve assembly in the gas domes is designed to safely vent gas from the digester at three times the monthly gas production rate; thus if one assembly fails, the second one can safely handle all the gas produced in the digester. The relief valves are set to release gas if the pressure exceeds 5 inches of water column above the normal digester battery gas main pressure or approximately 11 inches of water column. Backup Power Supply An uninterruptible power system (UPS) provides at least 2 hours of backup power supply to essential loads at the digester station. Pressure Switches The low pressure gas ( LPG) line from each digester contains a pressure gauge with local readout, a high pressure switch that closes at high pressures, a low pressure switch that closes at low pressures, and an orifice type differential pressure flow indicator with readout at the battery control panel. A low pressure alarm is also annunciated at the battery control panel. Pipeline The pipeline from the Hyperion Treatment System to the Scattergood Generating Station is equipped with manual shutoff valves that can be closed in the event of a significant pressure decrease in the pipeline. Flame Arrestor Flame arrestors are located immediately before pressure relief valves on digesters. Flame arrestors are baffled metal heat exchangers that prevent flames from entering the digester. Flares Flares are used to burn excess digester gas. Each digester is connected through a common line to a flare that is activated when the gas level in the low pressure gas holder reaches 90 to 95 percent capacity or when the gas line to Scattergood exceeds 38 pounds per square inch (psi). Site Control Entry to Hyperion Treatment Plant is controlled with a fence and gates, which are monitored by security guards. Visitors and contractors must be approved by Hyperion Treatment Plant staff prior to entry into the facility. Offsite Consequence Analysis Results Worst-case release scenarios were evaluated using the multienergy method for the effects of potential vapor cloud explosions for the Hyperion old digesters, low pressure gas holder and the interplant pipeline. The distance from the point of release to a location at which the flammable regulated substance concentration equals or exceeds a certain pressure (known as the flammable endpoint) was determined. As required by EPA and CalARP regulations, the digester gas flammable endpoint used was an overpressure of 1 psi. The RMP and CalARP regulations require that, for the worst-case release analysis, the release should be assumed to occur at ground l evel (0 feet). Accordingly, the worst-case release analysis was performed at this level. The passive mitigation provided by the hill east of the site was considered in the analysis. It will provide an additional mitigative influence. Analysis of the worst-case release scenarios for the digester gas process demonstrates that the endpoint distances are less than the distances to the nearest public receptor. Summary of the Accidental Release Prevention Program and Chemical-Specific Prevention Steps A prevention program is not required for Program 1 processes under CalARP regulations. However, Hyperion Treatment Plant is in compliance with Federal and State Process Safety Management (PSM) requirements. Chemical-specific prevention steps include staff awareness of the hazardous properties of digester gas and the presence of methane detectors and alarms. Hyperion Treatment Plant accidental release prevention program is based on the following key elements: 7 Commitment to safety by the Bureau of Sanitation facility management and staff 7 Comprehensive process safety information that is readily available to staff, emergency responders, and contractors 7 Comprehensive corrective and preventive maintenance program 7 A process hazard analysis 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 operations and maintenance staff participation 7 High level of training of operators and maintenance staff 7 Implementation of an incident investigation, inspection, and auditing programs by qualified staff |