WATER TREATMEMT PLANT - Executive Summary |
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A. The City of Fort Scott Water Treatment Plant 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 Water Treatment Plant emergency response policy involves the preparation of a response plan that is tailored to the facility itself and to emergency response services available in the community, and are in compliance with the EPA Emergency Response Program requirements. B. The City of Fort Scott Water Treatment Plant chlorine system was installed to disinfect the water supply for the City as well as for Bourbon County Consolidated Water District #2. The water treatment facility includes a chlorination room, which contains two (2) one ton chlorine cylinders, two chlorine vacuum regulators, flowmeters, ventilation system, and a chlorine alarm system. The treatment facility is manned 24 hour s per day, 365 days per year. Water treatment plant operators monitor the chlorine feed system at two hour intervals while the plant is in operation. C. The offsite consequence analysis includes consideration of two (2) chlorine release scenarios, identified as "worst case release" and "alternative scenario". The first scenario defined by the EPA, states that "the owner or operator shall assume that the maximum quanity in one 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 either the "toxic endpoint" selected by the EPA or 3 PPM, the Emergency Response Planning Guideline Level ERPG-2. This concentration is defi ned 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 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 Fort Scott Water Treatment Plant involves a failure of a single vessel (a total of approximately 2,000 lbs of chlorine). The offsite consequence analysis for this scenario was performed following conditions pre-defined by EPA, namely release of the entire amount as a gas in 10 minutes, use of the 60 minute average ERPG-2 as the toxic endpoint, and consideration of the population residing within a full circle with the radius corres ponding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis. However, one must consider the following: (1) Only about 26% of the total of the compressed liquefied chlorine released to the atmosphere flashes as a vapor. The remaining unflashed liquid forms liquid-driplet aerosols, resulting in the formation of a very dense chlorine cloud consisting of vapor and liquid droplets, with dispersion characteristics significantly different than a cloud consisting only of chlorine gas. (2) It is not appropriate to compare a 10 minute release to a 60 minute average standard. The 3 PPM 60 minute ERPG value can be modified using available time of exposure/concentration relationships to match the ten minute release time. (3) Only the population within an elliptical plume extending downwind of the release point is potentially affected. This plume area is approximately 6% of the area of the full circle. EPA-mandated meteoro logical conditions were used: Stability F, wind speed of 1.5 m/sec, highest temperature in the past 3 years (102 degree F), and a 65% average humidity. When atmospheric modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 2.6 miles and an estimate of residential population potentially affected was 8,500. The alternative release scenario involves a vessel leak resulting from a cylinder valve failure. The chlorine released is 317 lbs., over one hour of (10.5 lb/min), resulting in toxic endpoint distances to ERPG-2 and -3 levels. The latter is defined by AIHA as "the maximum airborn concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing life-threatening health effects." The typical meteorological conditionds used were Stability D, wind speed of 3.0 m/sec, average air temperature of 77 degrees F, and 50% average humidity. The estimated dista nces traveled to the toxic endpoints are 2,516 ft. for ERPG-2 and 903 ft. for ERPG-3. An estimated residential population of 1,000 potentially affected. Actuation of the chlorine detector is an active mitigation measure. An additional mitigation measure is that the chlorine feed is a vacuum type system. There is no pressurized chlorine piping in the system. This measure significantly reduces the chance of a major chlorine leak. The water treatment plant location in relation to the surronding terrain must also be considered. Approximately .8 mile west of the water treatment plant lies the Marmaton River, the City's water supply. The elevation of the river is 118 feet below the treatment plant elevation. If a release were to occur the decrease in elevation could cause the sinking characteristic of the chlorine gas to follow the river channel even against the wind or cross-wind. If this was the case there would be considerably less population affected than estimated i n both release screnairos. D. The general WTP accidental release prevention program is based on the following elements: 1. Operator training. 2. Preventive maintenance program. 3. Use of up to date process and safety equipment. 4. Use of effective operating procedures, written with operator participation. 5. Hazard review of equipment and procedures. 6. Implementation of a preventive maintenance and inspection program. 7. All operators have been trained on self-contained breathing apparatus (SCBA) and are aware of of the hazard and toxic properties of chlorine. E. No accidental releases of chlorine have occurred at this facility in the past five years. F. The facility has a Chlorine Emergency Response Plan, which has been reviewed by the City of Fort Scott Fire Department and the, Bourbon County Public Works Director, director of the Local Emergency Planning Committee. This program includes an emergency response decision tr ee and a notification plan. |