Terminal Island Treatment Plant - Executive Summary
The Terminal Island Treatment Plant treats municipal wastewater from the communities surrounding Los Angeles Harbor to reduce the communities' environmental impact on Los Angeles Harbor. During the biological treatment process, digester is generated as a byproduct when the solids extracted from the wastewater are stabilized. Terminal Island Treatment Plant uses this gas to fuel generators and boilers to assist in operating its plant process. Storing large quantities of digester gas can be hazardous. As the agency responsible for operating Terminal Island Treatment Plant, the City of Los Angeles Bureau of Sanitation takes safety obligations in storing and using digester gas as seriously as we take providing the environment with safe treated water. The following document describes what could happen if there were to be an accident, the steps taken every day to ensure safety, and what to do in event of an emergency.
Accidental Release Prevention and Emergency Response
The City of Los Angeles Bureau of Sanitation and Terminal Island Treatment Plant accidental release prevention policy 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 Terminal Island Treatment Plant has a process that generates, stores, conveys, and burns digester gas. This document summarizes our existing health and saf
ety programs, our internal management response procedures, and ongoing actions that are designed to prevent or minimize impacts of accidental releases of digester gas to the environment. The Terminal Island 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 Terminal Island Treatment Plant, originally built in 1935 and modernized between 1977 and 1981, is located at 445 Ferry Street in San Pedro, Los Angeles County, California. The plant is located on a 21.5-acre property. Wastewater treatment at Terminal Island Treatment Plant includes preliminary treatment, primary and secondary treatment, and coagulation/filtration before final discharge. The plant is designed to treat an average dry weather flow of 30 million gallons per day (mgd) and a peak dry weather flow of 55 mgd. Currently, the plant's inf
luent flow averages 16 mgd. The wastewater treated at the plant is discharged within the Los Angeles Harbor. The outfall is 6,000 feet long.
The facility currently generates and stores digester gas. Digester gas is a byproduct of the sludge digestion process. It is a mixture containing approximately 64 percent methane and 36 percent carbon dioxide along with other trace compounds. It is a regulated flammable substance under RMP and CalARP. Digester gas is stored in up to four digesters, a low-pressure gas holder, a high-pressure gas holder, and in facility piping. The digester gas process contains approximately 18,280 pounds of digester gas including 7,369 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.) Because the maximum quantity of digester gas stored at Terminal Island Treatment Plant exceeds the federal RMP and CalARP thresholds of 10,000 pounds, th
e facility is subject to federal RMP and CalARP regulations. The digester gas process at the Terminal Island Treatment Plant is categorized as a Program 1 process under federal RMP and
Digester Gas Safety Systems
The Terminal Island Treatment Plant has a number of safety systems designed to prevent accidental releases of digester gas. Several of these safeguards are described below.
Fire Protection System
Automatic fire sprinklers are located along the stairway to the top of each digester. The high-pressure gas sphere is equipped with a deluge system. Automatic fire sprinklers are also available in the power generation building. The boiler room and the gas compressor building contain portable fire extinguishers.
Leak Detection System
The gas compressor building has two stationary explosion meters, which will detect the presence of explosive gases and sound an audible alarm at 10 percent of the lower explosive limit (LEL). At the same time, the alarm signa
l is also sent to the main control room.
Pressure Relief Valves
Each digester has two pressure relief valves that release digester gas at 11 inches of water column pressure. Throughout the low-pressure gas system there are U-shaped condensate drain tubes. These tubes not only drain condensate, but also serve as pressure relief devices in case the pressure in the system exceeds the water height in the tubes. In the high-pressure gas system, there are two spring-loaded pressure relief valves on top of the high-pressure gas sphere. The pressure relief valves are set to relieve gas pressure in the high-pressure gas sphere at 50 psig.
Waste Gas Burners
The waste gas burners provide two separate units for wasting gas-one on line at all times and one on standby. Each unit consists of a waste gas burner with an automatic ignition system, a flame arrestor, and a back pressure regulator for maintaining proper pressure in the low-pressure gas system. In automatic mode, the operations of t
he waste gas burners are controlled by the level of the low-pressure gas holder.
Numerous pressure switches for the automatic and safe operation of the gas compressors and the waste gas burners are located both upstream and downstream of the gas compressors. The high-pressure switches on the high-pressure side stop the compressors when the pressure reaches 48 psig. A total of four low-pressure switches are on the gas compressors' suction side. These switches shut down compressors if a low-pressure condition exists. In addition, a high-pressure switch on the low-pressure side triggers the waste gas burners to burn gas under abnormal conditions.
Most of the gas handling piping is underground except when it has to be above ground near process equipment items. The above ground portion of the piping is mostly constructed of carbon steel. Cast iron pipes are used for underground piping.
Flame arrestors are baffled metal heat exchangers that
prevent flames from entering a vessel containing digester gas. Flame arrestors are located immediately before pressure relief valves on each digester. Flame arrestors are also located on the gas pipe next to each of the two waste gas burners. A flame arrestor is also installed on the digester gas line that leads to the boiler.
Entry to Terminal Island Treatment Plant is controlled with a fence and gates, which are monitored by security guards. Visitors and contractors must be approved by Terminal Island Treatment Plant staff prior to entry into the facility.
Offsite Consequence Analysis Results
Worst-case release scenarios were evaluated using the multienergy method for estimating the potential impact vapor cloud explosion for Terminal Island Treatment Plant digesters, low-pressure gas holder, and the high-pressure gas holder. The distance from the point of release to a location at which the flammable regulated substance concentration equals or exceeds a certai
n 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 pound per square inch (psi). The RMP and CalARP regulations require that, for the worst-case release analysis, the release should be assumed to occur at ground level (0 feet). Accordingly, the worst-case release analysis was performed for this level. The passive mitigation was not considered in the analysis. 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, Terminal Island Treatment Plant is in compliance with federal and State of California Process Safety Management (PSM) requirements. Chemical-specif
ic prevention steps include staff awareness of the hazardous properties of digester gas and the presence of methane detectors and alarms.
The Terminal Island Treatment Plant accidental release prevention program is based on the following key elements:
7 Commitments to safety by the Bureau of Sanitation facility management and staff
7 Comprehensive safety process 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 program using qualified staff