Water Reclamatiion Facility - Executive Summary |
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EXECUTIVE SUMMARY The City of Sanford, Florida is located 20 miles north of Orlando. It is the county seat of Seminole County, and has a utility service area population of approximately 42,000. City of Sanford Utility Department Mission Statement To provide utility customers of the City of Sanford with drinking water, sewerage service and reclaimed water in a safe, cost-effective, environmentally acceptable and approved manner. City of Sanford Risk Management Program The intent of the U.S. Environmental Protection Agency (EPA) Risk Management Program (RMP) regulations are to prevent and minimize the impacts of accidental releases of extremely hazardous substances. The City of Sanford Water and Wastewater Treatment Facilities fall under these new rules because they exceed the threshold for chlorine. Thus, to conform with RMP regulations (FR.61 [120], pg. 31668), the City of Sanford Facilities must meet the following RMP requirements by June 21, 1999, *Hazard Assessment *Prevention Program *Emergency Response Program *Risk Management Plan (RMPlan) The City of Sanford Utility Department 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 emergency response policy involves plans which 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. The City of Sanford Water Reclamation Facility (WRF) is located at 1201 W. Seminole Boulevard, Sanford. It is a 7.3 MGD rated plant which is designed to treat wastewater from the City's collection system to Public Access Quality Reclaimed Water. Chlorine is widely used not only for treating municipal and industrial water and wastewater supplies but also in the production of many dyes, insecticides, solvents and plastics. Chlorine gas is a severe respiratory irritant, and liquid chlorine is irritating to the skin. The gas has a pungent odor detectable at concentrations of less than 1ppm. A few breaths of 1000 ppm chlorine in the air is likely to be fatal. Chlorine gas is used in the final stages of the wastewater treatment process for the purpose of disinfecting the clear effluent. At the WRF gaseous chlorine is continuously fed to the Chlorine Contact Chamber to achieve a 1.5 to 2.0 ppm residual total chlorine level in the effluent. Ty pically, about 125 pounds per day of chlorine is used for every 1.0 mg gallons of effluent. Because chlorine poses a serious health risk if released to the atmosphere, chlorine is fed from one-ton containers through a fail-safe device called a chlorinator. A chlorinator system includes two main components, a vacuum regulator which mounts directly to the upper gas valve of the one-ton chlorine container by means of a lead gasketed positive yoke assembly, and an ejector which uses effluent flow to create the necessary vacuum. From the ejector the chlorine gas mixes with the effluent before being injected into the chlorine contact chamber through a diffuser. The feed system from the container to the ejector is operated under vacuum, so any small leaks pull in air instead of releasing chlorine. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative 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 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 released before its concentration decreases to the "toxic endpoint" selected by EPA of 3 ppm, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American 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 within a radius corresponding to the toxic endpoin t distance has to be defined, "to estimate the population potentially affected". The worst-case release scenario at the Water Reclamation Facility involves a failure of the one-container. The offsite consequences analysis for this scenario was performed for 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 full circle radius corresponding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis; however, the assumptions used may be unrealistic because: (1) Only a fraction (about 26% of the total) of the compressed liquefied chlorine released to the atmosphere flashes as a vapor. The remaining unflashed liquid forms liquid-droplet aerosols. This results in the formation of a very dense chlorine cloud consisting of vapor and liquid droplets, with dispersion characteristics signific antly different than for a cloud consisting only of chlorine gas. (2) It is not appropriate to compare a 10-minute release to a one-hour average standard. The 3ppm one- hour ERPG calue can be modified using available time of exposure/concentrations relationships to match the ten-minute release time; the value obtained is 7.3 ppm. (3) Only the population within an elliptical plume extending downwind of the release point is potentially affected. This plume area, or footprint, is approximately 6% (one-twentieth) of the area of the full circle. EPA-mandated meteorological conditions, namely Stability F, wind speed of 1.5 m/sec, highest daily maximum temperature (116 Degrees F), and average humidity (65%) were used for both sets. When atmospheric dispersion modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 1.30 miles and an estimate of residential population potentially affected of 8,716 people was obtain ed. When atmospheric dispersion modeling for the alternative release scenario was performed using the TRACE 8.0 assumptions, a distance to toxic endpoint of .30 mi miles and an estimate of residential population potentially affected of 946 people was obtained. The alternative release scenario involves a gas valve remaining open (gas release). The typical meteorological conditions use were Stability B, wind speed 3.0 m/sec. Actuation of the chlorine detector is an active mitigation measure considered. An additional mitigation measure is the vacuum-type chlorinator and piping which significantly reduces the amount of chlorine released in case of rupture. The general City of Sanford Utility Department Accidental Release Prevention Program is based on the following 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, written with the particip ation of the operators * Performance of a hazard review of equipment and procedures * Implementation of an inspection program Chemical-specific prevention steps include availability of self-contained breathing apparatus (SCBA), worn by the operators during connection/disconnection of chlorine supply, awareness of the hazardous and toxic properties of chlorine, and presence of chlorine detectors. No accidental releases have occurred at this facility in the past five years. The facility has an emergency response program, which has been coordinated with the City of Sanford Fire Department, and the Seminole County Department of Public Safety which a member of the Local Emergency Response Planning Committee (LEPC). |