City of Gallup Wastewater Treatment Plant - Executive Summary
Executive Summary |
In June 1996, the U.S. Environmental Protection Agency (EPA) issued Risk Management Program (RMProgram) regulations (40 CFR, Part 68). Regulated under the Clean Air Act Amendments (CAAA), Section 112(r), the RMProgram requires facilities that store large amounts of listed hazardous chemical substances to prepare and implement risk management plans to reduce the probability of accidental releases and minimize the health risks to the public and the environment. The RMProgram regulates 77 listed toxic substances and 63 listed flammable substances. The RMProgram regulations apply to an estimated 7,200 public and private drinking water and wastewater treatment facilities nationwide where chlorine, ammonia or sulfur dioxide are used. When properly used, chlorine, ammonia and sulfur dioxide have proven to be both safe and effective.
The Gallup Wastewater Treatment Plant (GWWTP) in Gallup, New Mexico is the City of Gallup's only wastewater treatment plant, currently s
erving over 20,000 people in the area. The GWWTP receives, treats and releases wastewater from residential, commercial and industrial sources. The facility stores and uses only two regulated chemicals, anhydrous chlorine and sulfur dioxide, in quantities higher than the threshold quantities. The terms anhydrous chlorine and chlorine are used interchangeably and specifically refer to a chemical listed in the RMProgram regulations.
The chlorine is used in the chlorination process to disinfect wastewater. Chlorine is stored within a building in three 1-ton containers. The total maximum intended inventory is 6,000 pounds. The chlorine is liquified under pressure in the containers. Chlorine is drawn as a gas from the 1-ton containers through a vacuum feed system. The gaseous chlorine is then metered into a solution through two chlorinators. The chlorine solution is then fed to various chlorine feed points. The sulfur dioxide is used in the dechlorination process in which sulfur d
ioxide reacts with water and hypochlorous acid created by the chlorination process. The hypochlorous acid must be removed from the wastewater prior to discharging the effluent into the Puerco River because hypochlorous acid has detrimental effects on aquatic life. The sulfur dioxide is stored in the dechlorination storage building in eight 150-pound cylinders. The maximum intended inventory of sulfur dioxide is 1,200 pounds. The facility is subject to the Occupational Safety and Health Administration (OSHA) Process Safety Management (PSM) Standard and therefore, the chlorination and dechlorination processes are subject to the Program 3 RMProgram Regulations.
The major driving force in the development of the RMProgram regulations is reducing the risk to public health by minimizing the potential of a chemical release. The GWWTP has a multi-layer system in place to meet this goal. The RMProgram includes the following: (1) properly trained operators to safely handle
chlorine and sulfur dioxide; (2) leak detectors located where chlorine and sulfur dioxide are stored and/or used; and (3) chemical release prevention and emergency response plans in place. Trained personnel respond to alarms to assess whether a release poses an imminent danger to employees or the public. While a significant release is unlikely, the emergency response plans have been developed for just such an occurrence. The emergency response plans include procedures to be followed by operators trained to take appropriate action including contacting the City of Gallup Fire Department and New Mexico State Police.
Within the management and administrative roles of the GWWTP, responsibility has been defined to coordinate and implement the RMProgram. Overall development and management of the RMProgram is the responsibility of the RMProgram Manager. The Wastewater Systems Superintendent is the designated RMProgram Manager. The RMProgram Coordinator reports to the RM
Program Manager and is responsible for the day-to-day coordination and implementation of the RMProgram. The Wastewater Systems Assistant Superintendent is the designated RMProgram Coordinator. The RMProgram Coordinator will delegate various GWWTP operators to assist in the implementation of the RMProgram. Additional program oversight is provided by the City of Gallup's Utilities Director and Risk Management Director who act as auditors of the program's implementation and overall quality.
Worst Case and Alternative Release Scenarios
EPA requires facilities subject to RMProgram regulations to evaluate potential off-site consequences of chemical releases. As part of the consequence analyses, EPA requires that one release representing the worst case release scenario for toxic regulated substances above the threshold quantity be modeled. In addition, EPA requires that one release representing the worst case release scenario for flammable regulated substances present above the threshol
d quantity be modeled. If there is more than one toxic and/or flammable regulated substance present above the threshold quantity, EPA only requires the substance with the largest worst case scenario to be modeled if the other substance(s) worst case scenario is completely within the largest worst case scenario. In addition to worst case scenario modeling, alternative release scenarios representative of each toxic and flammable substance present above the EPA threshold quantities must be modeled. As mentioned above, chlorine and sulfur dioxide are the only regulated substances above the threshold quantity used by the GWWTP.
To evaluate the potential effect of a worst case or alternative release scenario, a distance to a toxic endpoint is determined. The endpoints for toxic chemicals for the RMProgram scenarios are based on the American Industrial Hygiene Association (AIHA) emergency response planning guidelines level 2 (ERPG-2). ERPG-2 is defined as the maximum airborne concentrat
ion below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action. The toxic endpoint that is calculated for a particular release scenario is used to determine the potentially affected geographical area and population. The ERPG-2 is 0.0087 milligrams per liter (mg/l) for chlorine and 0.0078 mg/l for sulfur dioxide.
EPA states that a "worst case scenario" is useful for encouraging "community dialogue". However, because the worst case scenario does not necessarily represent events likely to occur, it is more useful for discussion purposes than for emergency planning purposes. An "alternative release scenario" is a release scenario more likely than the worst case scenario and should be used for emergency response planning.
The GWWTP stores chlorine within its property boundary in 1-ton containers.
To comply with RMProgram regulations, a worst case scenario was conducted assuming the release of the contents of 2,000 pounds (1-ton) of chlorine in 10 minutes. Because the 1-ton containers are located in a building, the worst case scenario was modeled considering the building as a passive mitigation factor. The resulting distance to the toxic endpoint is 2.2 miles, affecting an estimated population of 1,600. Sensitive receptors that potentially could be affected if the worst case scenario were to occur include a school, a park with soccer fields, four religious institutions and Gallup-McKinley County Airport.
The GWWTP stores sulfur dioxide within its property boundary in 150-pound cylinders. To comply with RMProgram regulations, a worst case scenario was also conducted for sulfur dioxide assuming the release of the contents of 150 pounds of sulfur dioxide in 10 minutes. Because the 150-pound cylinders are located in a building, the worst case scenario was modeled considering
the building as a passive mitigation factor. The results of the worst case scenario modeling effort for sulfur dioxide yielded a distance to toxic endpoint of 0.6 miles. If this scenario were to occur, it would be completely within the worst case scenario for chlorine. As stated above, EPA only requires the substance with the largest worst case scenario (chlorine for this facility) to be modeled if the other substance (sulfur dioxide for this facility) is completely within the largest worst case scenario. Therefore, it is not necessary to report the worst case scenario modeling results for sulfur dioxide at the GWWTP.
The alternative release scenario for chlorine was evaluated for emergency response planning purposes. The alternative release scenario for chlorine is the shearing off of a 1-ton chlorine container valve caused by the mishandling of a container during unloading. This scenario results in a gaseous release of chlorine. The alternative release scenario resulted in a
n endpoint distance of 0.2 miles. A population of approximately of 10 people could potentially be affected if this scenario were to occur. The alternative release scenario for sulfur dioxide is the shearing off of a 150-pound sulfur dioxide cylinder valve caused by the mishandling of the cylinder during unloading. This scenario results in a gaseous release of sulfur dioxide. The alternative release scenario resulted in an endpoint distance of 0.3 miles. A population of approximately 20 people could potentially be affected if this scenario were to occur. In addition a nearby park with soccer fields could potentially be affected if this scenario were to occur.
5-Year Accident History
Any accidental releases from covered processes that resulted in deaths, injuries, or significant property damage on-site, or known off-site deaths, injuries, evacuations, sheltering in place, property damage, or environmental damage must be reported in the RMProgram submission to EPA. Based upon inte
rviews with plant operations, maintenance, safety, and training staff and management, no major chemical release has occurred at the GWWTP in the last five years.
Chemical Release Prevention Program
The GWWTP has a chemical release prevention program in place for the use chlorine and sulfur dioxide in the facility's chlorination and dechlorination processes, respectively. Key provisions of the prevention program are as follows:
* Written procedures have been prepared for the use of chlorine and sulfur dioxide, including directions for safe startup, normal and shutdown operations and emergency shutdown.
* Employees who operate the chlorination and dechlorination systems must receive training initially and periodically on safe startup and shutdown operations and emergency shutdown.
* Incidences, including minor releases are investigated to improve the safety of the chlorination and dechlorination processes.
* Once completed, incident investigations are shared with employees.
A process hazard analysis, which identifies potential hazards and ways to improve the safety of the chlorination and dechlorination processes, is conducted every five years, or when significant changes are made to the process.
* A maintenance program is in place to prevent accidental chemical releases that may result from mechanical failure of improperly maintained equipment. Maintenance practices are consistent with guidance provided by the Chlorine Institute and Compressed Gas Association.
* Compliance audits are conducted every three years to evaluate the RMProgram and its implementation for compliance with EPA RMProgram regulations.
Emergency Response Program
The GWWTP has an emergency response program in place. This program consists of personnel trained to recognize releases, assess the situation, and engage the proper emergency response personnel. When external emergency response is required, GWWTP personnel will notify the City of Gallup Fire Department and/or New Mexico S
tate Police then establish an incident command system. Incident command is transferred to the Fire Department or the New Mexico State Police upon their arrival. GWWTP personnel familiar with the chlorination and dechlorination processes remain on-site to assist the emergency response agencies if necessary. The Fire Department and New Mexico State Police have access to additional emergency response resources, including the Local Emergency Planning Committee, Highway and Transportation Department, Department of Health and the EPA.