Deer Island Treatment Plant - Executive Summary

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Massachusetts Water Resources Authority 
Deer Island Treatment Plant 
Winthrop, Massachusetts 
The Massachusetts Water Resources Authority (MWRA) operates the Deer Island Treatment Plant (DITP) in Winthrop, Massachusetts, which is subject to U.S. Environmental Protection Agency (EPA) regulations governing Accidental Release Prevention (ARP) Requirements: Risk Management Programs under Section 112(r) of the Clean Air Act (40 CFR Part 68).  The DITP is subject to this regulation due to the presence of a flammable gas, methane, which is a component of digester gas. This Risk Management Plan (RMP) has been developed in accordance with the requirements specified under 40 CFR Part 68, Subpart G.  The RMP certifies that the DITP has instituted a Risk Management Program that is in compliance with U.S. EPA ARP Program 2 requirements.  
The RMP includes an Executive Summary and Data Elements following the format published by U.S. EPA.  This document identifies the applicable corpo 
rate policies and risk management systems, including comprehensive accident prevention and emergency response programs.  In addition, this RMP identifies a set of worst case and alternative release scenarios, the potential off-site consequences of those releases, and the facility's five-year accidental release history.  This RMP certifies that prevention and emergency response programs are in place so as to minimize risks to workers and the potentially affected public.    
1.1    Overview 
MWRA strives to conduct its business in strict conformity with all applicable laws and in a safe and responsible manner. MWRA places the very highest priority on the safety and health of its employees and members of the communities in which it operates.  This policy applies to the Winthrop, Massachusetts DITP and to all the locations of MWRA and to all materials which may be hazardous to health.   
The occupational safety and health of the  
Authority employees and well-being of our neighbors is a matter of paramount concern.  The Authority is committed to ensuring that its facilities and work sites are safe and that all employees observe safe work practices and are properly equipped to perform their assignments.  To achieve that objective, the Authority employees Board certified safety and health professionals, who are continuously developing and implementing a comprehensive and effective occupational and safety health program.  The program must reflect the requirements of relevant laws and regulations, generally accepted standards and the dictates of common sense.   
The immediate health and safety of all Authority personnel and the public is a primary concern in the procurement of all safety-related equipment.  If an emergency/critical situation should arise, the Division Director, DITP Director and professional staff responsible for occupational safety and health are contacted immediately. Safety is part of everyone's  
job.  Therefore, each employee of the Authority shall comply with this program and adhere to all approved safety standards and procedures.  This program includes specifically identified responsibilities for all employees including, line supervisors, managers, directors, construction engineers, and health & safety staff. It also includes requirements for health and safety, operations, and emergency response training. The MWRA policy also establishes requirements for notification, reporting and investigating imminent hazards, potential hazards, accidents and injuries.  Site safety surveys, safety inspections and safety "audits" are performed under the direction of the DITP Safety Supervisor who reports the findings to the appropriate managers, directors, and committees. 
1.2    Risk Management System 
DITP  has developed a management system to implement and maintain compliance with the Accidental Release Prevention (ARP) and related chemical safety and emergency response programs.  This man 
agement system identifies lines of responsibility for the entire program and each of its key elements: 
* Accidental Release Prevention Program: Director, Deer Island Treatment Plant 
* Off-Site Hazard Assessment: Field Safety Supervisor 
* Prevention Program: Deputy Director of Operations and Maintenance Support 
* Emergency Response Program: Field Safety Supervisor   
The Deer Island Treatment Plant processes and treats wastewater from Boston-area communities.  The waste is pumped into storage tanks where it is consumed by micro-organisms, which remove solids and a majority of toxic chemicals.  The remaining sludge is further processed in sludge digesters where it is mixed and heated to reduce its volume and kill disease-causing bacteria.  Gas is produced in the digesters by the action of anaerobic bacteria. Digester gas typically contains about 62 percent methane, 2 - 4 percent hydrogen sulfides and a remainder of mostly carbon di 
oxide.  Digester gas is transported via pipe from each of 12 egg-shaped digesters to two digester gas holding tanks.  The gas is then cleaned, compressed and transported via underground pipe to the DITP Thermal Power Plant, the North Main Pump Station and a free standing fuel cell, where it is used as fuel.  Digester gas that is not consumed for power generation is incinerated in three flares.  The digesters are equipped with pressure safety relief valves that vent excess gas to the atmosphere to prevent structural failure associated with over-pressurization.  The digester gas system is designed to prohibit the build-up of significant flammable quantities of methane in the atmosphere.   
The maximum total estimated amount of methane in the entire digester gas process is about 68,000 lb.  Because this exceeds the 10,000 lb threshold for methane established under ARP, this process is regulated under 40 CFR Part 68.  No other toxic or flammable substances that are regulated under ARP are  
present in threshold quantities at the DITP.    
EPA has established three Programs by which facilities are to comply with ARP.  Program 1 applies to any facility that in the past 5 years has not had an accident that adversely affected the public or environment and for which the worst-case release would not affect public receptors.  The requirements for Program 1 are to register with EPA and certify that public receptors would not be affected and that off-site emergency responders have been notified of the on-site hazards.  Because during the ongoing construction phase,  MWRA prohibits public access to Deer Island and the hazards associated with methane are localized, the DITP presently qualifies for Program 1 ARP status.  However, once construction has been completed, there are plans to establish public access along the perimeter of Deer Island for recreational purposes.   Because this will result in the potential  presence of public receptors within the modeled impact area, once this 
area is open to the public the facility would become ineligible for Program 1 status.  
For this reason the MWRA has implemented an ARP program and is filing the Risk Management Plan according Program 2 requirements.  These requirements include the assessment of worst-case and alternative releases, review of the 5-year accident history, and an accident prevention program. DITP is subject to Program 2 because it is not listed among the 9 Program 3 NAICS codes specified in the regulation and is not subject to the U.S. Occupation Safety and Health Administration Process Safety Management Program.  
3.0   Off-Site Hazard Assessment 
For the purposes of developing and maintaining adequate RMP's, the EPA has defined in its governing rules and guidance a series of modeling methods and assumptions which are to be utilized as administrative guides for planning purposes.  In order to standardize and simplify to a practical level the many factors that can potentially occur in an accidental rele 
ase situation, some of these assumptions may not take into account the available preventive measures or mitigation methods that would diminish or even eliminate the implied risks that are suggested by "worst-case" analyses.  For that reason, both the results for the standardized "worst case" defined by the EPA methods and an alternative case, which is believed by DITP to more realistically represent situations that may possibly, but rarely, occur within the lifetime of the facility, are presented and described.  The actual incident history for this facility over the last five years has been reviewed.  No accident has resulted in reportable on-site injury, off-site injury, emergency response, or damage to property or the environment 
3.1    Worst Case Release for Flammable Substances 
The worst case for flammable substances is defined as a vapor cloud explosion involving the largest amount of a regulated substance in a single vessel.  The endpoint is a 1 psi overpressure, which represents  
a pressure at which damage to structure could take place. The largest vessel containing a regulated flammable substance at the Deer Island facility is a digester gas storage tank containing 21,000 lb of methane.  Applying EPA's RMP*CompTM program results in an estimated worst-case endpoint distance of 0.2 miles.  This distance extends to adjacent waters but does not impact any residential or commercial areas.  It will however, cover small portions of the planned public walkway that will surround the facility.  
3.2    Alternative Flammable Release 
The alternative release is a leak from a digester gas compressor located inside the compressor  building.  It is assumed that a sufficient quantity of digester gas is released that the concentration approaches the upper flammability limit.  It then assumed that a vapor cloud explosion occurs. Again, the endpoint used is a 1 psi overpressure and applying RMP*CompTM indicates an endpoint distance of 0.1 mi.  This alternative release affects the p 
lanned public walkway and adjacent waters but does not affect other public or environmental receptors.  
DITP has measures in place to prevent and mitigate potential releases of toxic and flammable substances.  These include flammable gas detectors, pressure relief vents, alarms, and fire detection and suppression systems.   
Although, consistent with ARP regulations,  the DITP currently qualifies for Program 1 status, DITP is instituting a Program 2 Accident Prevention Program that consists of the following elements: 
     Safety Information  including MSDS for methane and, for each portion of the digester gas process, safe upper and lower operating parameters, equipment specifications and applicable codes and standards.  
       Hazard Review, including a systematic evaluation of potential hazards associated with production, storage and transport and use of digester gas and development of recommendations for improving safety. 
       Operating Procedures  regarding vario 
us portions of the digester-gas system. 
       Training  of workers on health and safety, operating procedures and EPA's Accidental Release Prevention program. 
   Maintenance system and procedures to maintain mechanical integrity of the process components  and associated equipment. 
       Incident Investigation  procedures to document incidents that involve the release  of  digester gas. 
       Compliance Audit  of the prevention program to be conducted in 1999 and at least every three years. 
During the past 5 years (June 1994 to June 1999), there has been a single accident (March 1999) involving digester gas that qualifies for reporting under 40 CFR Part 68.  The incident involved a minor release  (estimated to be less than 10 lb) of digester gas from a compressor located inside a concrete building.  The amount of gas released was limited by isolation valves that engaged and the damage associated with an isolated gas fire was limited to the compressor, requi 
ring replacement of the compressor and associated fittings.  The incident investigation has tentatively concluded that the release was due to a faulty component in the compressor. It is MWRA's estimation that the cost for replacing the equipment that was damaged in this incident, estimated at $50,000, requires that this incident be reported in the RMP. This incident and no other accidental release of digester gas at the DITP within the past 5 years has  resulted in any of the following reporting criteria:   reportable on-site injury, off-site injury, off-site evacuation or sheltering in place, or damage to off-site property or the environment. 
It is the policy of DITP to place the highest priority on employee safety and health and on protection of the community from all plant-induced environmental conditions.   The Deer Island Treatment Plant Crisis Management Plan incorporates provisions to safeguard worker safety and to notify local response agenci 
es that have the primary responsibility for emergency response to digester gas leaks, fires and explosions at the DITP.  These agencies (Winthrop and Boston Fire Departments) have been informed of the hazards present at the DITP and the design of the digester gas system.  The DITP Emergency Response Team (ERT) is trained and prepared to isolate workers from areas of potential harm in the event of a digester gas leak and to communicate with off-site emergency responders.  The ERT , however, is not expected to undertake fire-fighting activities associated with digester gas releases. 
DITP has organized its management system to effectively address all hazards and potential risks. Personnel training are necessary to support a continual improvement in facility safety.  These programs are all documented so that needed information about the safe handling of all chemicals present at the facility is available to employees, and can be readily interprete 
d by emergency response team staff and the Site Emergency Coordinator when questions arise from public safety officials on potential risks to the community.  All of these features of the RMP and the integrated risk management program at this site lead to operations that are safe today, but will be even safer tomorrow.
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