Wastewater Treatment Plant #1 (WWTP #1) - Executive Summary |
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EXECUTIVE SUMMARY A. The City of Harlingen Waterworks System (HWWS) accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the U.S. Environmental Protection Agency (EPA) Prevention Program are adhered to. The HWWS emergency response policy involves the preparation of response plans that are tailored to each facility and to the emergency response services available in the community, and is in compliance with the EPA Emergency Response Program requirements. B. The Wastewater Treatment Plant (WWTP #1) has been installed to disinfect and treat the flow of domestic wastewater prior to discharge into the Arroyo Colorado River. The facility is located at 1102 E. Taft Street. The plant utilizes a chlorinating station, liquid chlorine containers, a chlorinator, various safety equipment, an instrument room containing flow recorders, various electrical panels and additional safe ty equipment. The amount of chlorine on site is four one-ton containers with one on-line and three on standby. Water treatment operators are at the facility daily and respond to any trouble alarms that may occur. C. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst-case release" and "alternative release scenario". The first scenario is defined by EPA, which states that "the owner or operator shall assume that the maximum quantity in the largest vessel is released as a gas over 10 minutes" due to an unspecified failure. The alternative release scenario is defined as "more likely to occur than the worst-case release scenario". Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine release before its concentration decreases to the "toxic endpoint" selected by EPA of .0087 mg/L, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the Am erican Industrial Hygiene Association (AIHA) as the "maximum airborne concentration 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 which could impair an individual's ability to take protective action." The residential population within a circle with a radius corresponding to the toxic endpoint distance has to be defined "to estimate the population potentially affected". The worst-case release scenario at the Wastewater Plant #1 involves a failure of the one-ton (2,000 lb.) container that is connected to the system. The offsite consequence analysis for this scenario was performed. The pre-defined conditions set by EPA, namely the release of the entire amount as a gas in 10 minutes, use of the one-hour average ERPG-2 as the toxic endpoint, and consideration of the population residing within a full circle with radius corresponding to the to xic endpoint distance. EPA - mandated meteorological conditions, namely Stability F, wind speed of 1.5 m/sec, air temperature (77?F), and average humidity (50%) were used. When atmospheric dispersion modeling for the worst-case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 1.3 miles and an estimate of residential population potentially affected of 4,700 was obtained. The alternative release scenario involves the rupture of the flexible connection (pigtail) connected to the one-ton container. The amount of chlorine released is 317 lbs., at an average rate over one hour (the duration of the release) at 10.5 lbs./min. to toxic endpoint distances to the ERPG-2 level. D. The general HWWS accidental release prevention program is based on the following key elements: * High level of training of the operators * Preventive maintenance program * Use of state-of-the-art process and safety equipment * Use of accurate and effective operating procedures * Performance of a hazard review of equipment and procedures * Implementation of an audit and inspection program Chemical-specific prevention steps include availability of self-contained breathing apparatus (SCBA), worn by the operators during connection / disconnection of the chlorine supply, awareness of the hazardous and toxic properties of chlorine, and presence of chlorine detectors. E. No accidental releases of chlorine have occurred at this facility in the past five years. F. The facility has an emergency response program that has been reviewed by the Harlingen Fire Department. This program includes an emergency response decision tree and a notification plan. Emergency response drills and drill evaluations will be conducted every six months; emergency operation and response procedures will also be reviewed at that time. G. Changes to improve safety (recommended actions) will be reviewed upon completion of a facility Hazard Assessment a nd Compliance Audit. 17 1 |