Southwest Water Pollution Control Plant - Executive Summary

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Executive Summary 
Chemicals are widely used in industry and in the home, as well as present in the environment.  They are transported on roads, waterways, and railways.  We at the Southwest Water Pollution Control Plant (Southwest WPCP) use chemicals too.  For example, we produce methane as a part of our wastewater treatment process. Storing large quantities of methane can be a hazard.  We take our safety obligations in storing and using methane as seriously as we do providing the effective, safe treatment of wastewater.  The following document describes what could happen if there were to be an accident, the steps we take everyday to ensure a safely operating plant, and what to do in event of an emergency.   
Accidental Release Prevention and  Emergency Response Policies 
The Philadelphia Water Department (PWD) and Southwest WPCP policy involves a unified approach that integrates proven technology, trains staff on operation and maintenance practices, and uses tested manag 
ement system practices.  All applicable procedures of the 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 U.S. Environmental Protection Agency's (EPA's) Risk Management Program, under Section 112 (r) of the Clean Air Act (CAA) Amendments of 1990, 40 Code of Federal Regulations (CFR) Part 68. The Southwest WPCP has a sludge digestion system that produces methane as a by-product of the process. The Southwest WPCP has prepared a detailed and comprehensive emergency response plan to handle any potential accidental releases that is designed to safeguard both on- and off-site people. To date, we have had an excellent record in preventing accidents from occurring. 
General Facility and Regulated Substances Information 
The Southwest WPCP, operating since 1954, is located at 8200 Enterprise Avenue in the City of Philadelphia. Wastewater t 
reated at the Southwest WPCP is discharged to the Delaware River.  The treated wastewater meets all EPA standards. This wastewater treatment includes preliminary screening,grit removal, primary sedimentation, secondary sedimentation, and chlorination before final discharge.  The Southwest WPCP discharges up to 300 million gallons per day (MGD) of treated wastewater, with an average flow of between 180  to 200 MGD. 
The facility currently produces methane as a by-product of its wastewater treatment process. Methane is a regulated flammable substance under 40 CFR Part 68 - RMP.  The Plant's methane storage exceeds the listed threshold quantity in the RMP Regulations. 
Methane is produced at the plant as a result of the digestion of sludge from the wastewater treatment process. This is a naturally occurring process that happens in swamps and other locations.  Methane leak detector monitors continuously check for leaks in the digester tank areas. These alarms are annunciated at the central a 
nd local control panels at the plant in the main control room. In the case of a leak, each area has an audible alarm and red flashing warning light to indicate the presence of methane above safety threshold limits. The leak detectors are set to alarm at 25% of the lower explosive limit (LEL) for methane that is well below potential explosive levels.  
The sludge digesters and storage tanks are equipped with pressure relief valves that enhance the safety of the system.  The process rooms are equipped with a ventilation system that operates continuously to ensure no build-up of digester gas that could pose an explosive concern.  
The Southwest WPCP is controlled at Enterprise Avenue by a card access gate.  Visitors and contractors must check-in at the administration building and be approved by Southwest WPCP staff prior to entry into the facility.  The plant is manned 24-hours a day, year round, and alarms notify staff of any problems or situations that require follow-up investigations at  
all times.       
Offsite Consequence Analysis Results 
The offsite consequence analysis includes consideration of one release scenario, identified as "worst case" release scenario. The worst case scenario assumes that the entire content of the largest single container of digester gas is released and instantaneously explodes, regardless of how improbable that may be.  In addition, only "passive" mitigation methods, such as buildings can be considered.  Passive mitigation, as defined, requires no mechanical, electrical, or human input. The regulations require that the worst case scenario assume atmospheric conditions that are conservative and result in large impact areas. 
The worst-case release scenario for methane is focused on the 110-foot diameter sludge digesters that produces the gas. The scenario used for Southwest WPCP is a release of 2887 pounds of methane and an instantaneous explosion hazard.     
The explosion could be caused by catastrophic events, such as an airplane crashing  
into the digester. In practice this type of an explosion would be unlikely and never occur during the lifetime of the plant. The results of the worst-case release analysis indicates that this scenario has no offsite impacts.  Thus, an alternative release scenario is not required for this process. 
Five-year Accident History Summary 
No methane explosions that could have caused safety or health hazards to any individuals at on-site or off-site locations (no deaths, injuries, property or environmental damage, evacuations, or sheltering in place) occurred at Southwest WPCP during the last five years.  This process qualifies for RMP Program 1 because its worst-case release scenario stays on-site and the process has had no accidents in the past five years. 
Prevention Program Summary 
The Southwest WPCP's accidental release prevention policy involves a unified approach that integrates proven technology, trains staff on operation and maintenance practices, and uses tested management system pract 
ices.  Under the RMP Program 1 requirements, Southwest WPCP is not required to have a formal prevention program.  However, they have many elements and policies in place currently that have been effective in preventing accidents from occuring in the digester gas system. 
Southwest WPCP's informal prevention program is based on the following key elements: 
* Detailed management system and clear levels of responsibilities and team member roles 
* Comprehensive safety process information that is readily available to staff, emergency responders,  and contractors 
* Comprehensive preventive maintenance program 
* Use of state-of-the-art process and safety equipment 
* Use of accurate and effective operating procedures 
* High level of training of operators and maintenance staff 
* Implementation of an incident investigation, inspection, and auditing program using qualified staff. 
After reviewing Southwest WPCP existing informal prevention program, no additional measures are necessary to prevent off- 
site impacts from accidental releases of digester gas. 
Emergency Response Program Summary 
Southwest WPCP has coordinated its emergency response actions with the City of Philadelphia Fire Department HAZMAT Unit, which is a member of the Local Emergency Response Planning Committee (LEPC). Emergency evacuation drills are conducted at a minimum frequency of every 12 months. 
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