Ashland Water Treatment Facility - Executive Summary |
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Executive Summary Accidental Release and Emergency Response Policies The City of Lincoln Ashland Water Treatment Facility (WTF) has operated their disinfection process with only one minor incident within the last five years. This successful operating record is due to the City's commitment to ongoing training programs, operating procedures, and computer-generated maintenance activities. Stationary Source and the Substance Handled The City of Lincoln operates a water treatment facility in Ashland, Nebraska. The facility uses chlorine to reduce the pathogenic (disease causing) bacteria and viruses in potable water to less than the maximum contaminant levels set forth in the Safe Drinking Water Act. Chlorine utilized in the disinfection process arrives at the facility in one ton containers that are stored in a ventilated building equipped with leak detection devices and an air scrubber unit. Chlorine also arrives at the facility in 150-pound containers that are placed by dolly in to a designated area of the chlorine process area. The maximum quantity of chlorine stored at the facility is 35,000 pounds. Off-Site Consequence Analysis One worst-case release scenario and one alternative release scenario were assessed for the chlorine process. To ensure a common basis for comparisons, EPA defined the worst-case scenario as the release of the largest quantity of a regulated substance from a single vessel or process line that results in the greatest distance to an endpoint. The worst-case scenario allows consideration of passive mitigation measures. The worst-case release scenario for the chlorine process was determined in accordance with the requirements provided in 40 CFR 68.22 and 40 CFR 68.25(b,c). The alternative release rate is a release that is considered more reasonable or "more likely." The alternative release scenario for the chlorine process was determined in accordance with the guidelines in 40 CFR 68.22 and 68.28. Active mitigation measures, as w ell as passive mitigation measures, can be used in determining the alternative release scenario. According to EPA, the toxic endpoint for chlorine has been defined to be 0.0087 mg/L (3 ppm). An airborne concentration that is used as the toxic endpoints is the maximum airborne concentrations below which it is believed that nearly all individuals can be exposed for up to one hour without experiencing or developing irreversible or other serious health effects. The distance to the toxic endpoint becomes a radius for a circle around the covered process. Residential population within the circle is required to be determined based on available census information. The population number is reported as part of the EPA submittal. This method greatly overestimates the population potentially exposed to a chlorine release because the chlorine plume would seek lowest elevations in the direction of the prominent winds. Since wind direction cannot be anticipated for an accidental release, EPA man dated the circle estimation method. Release scenarios and distances to toxic endpoints are discussed in more detail in the subsequent paragraphs. Chlorine Worst-Case Release Scenario For the chlorine process at the Ashland WTF, the worst-case release results from a one-ton chlorine cylinder (maximum amount held in a single vessel) rupturing when unloaded from the delivery truck and its contents escaping to the atmosphere in 10 minutes. In the event the cylinder would release its entire contents to the atmosphere in 10 minutes, the release rate would be 200 pounds per minute. The distance to the toxic endpoint worst-case release distance, 1.3 miles, was taken from Exhibit 4-3 of the EPA's Risk Management Program Guidance for Wastewater Treatment Plants, for an urban setting. The residential population within the 1.3-mile radius of influence was determined to be approximately 300 people. The population was calculated by utilizing the U.S. Department of Commerce software package L andViewTM III, which sums 1990 population information from the Census Bureau for areas within the 1.3-mile radius impact zone. Alternative Release Scenario The alternative release scenario, or scenario more likely to result in a release, involves a failure of the lead gasket used for sealing the valve connection. This scenario results in a release of less than 2 pounds of chlorine gas for 20 minutes. It is assumed that the air scrubber turns on at 3 ppm chlorine, which discharges 5 ppm chlorine at a rate of 500 cfm. This results in a release rate of less than 0.1 pounds per minute. The distance to the toxic endpoint alternative release distance, less than 0.10 miles, was taken from Exhibit 4-15 of the EPA's Risk Management Program Guidance for Wastewater Treatment Plants, for an urban setting. The residential population within the 0.10-mile radius of influence was determined to be 0 people. The population was calculated by utilizing the U.S. Department of Commerce software pac kage LandViewTM III, which sums 1990 population information from the Census Bureau for areas within the 0.10-mile radius impact zone. Accidental Release Prevention Program The City of Lincoln has developed a Prevention Program in accordance with the requirements of 40 CFR 68 for Program Level 2. The City will continuously evaluate and update their safety and prevention procedures as needed. The City conducted a process hazard review for the process determined to be "covered", the chlorine process, as part of the development of the Risk Management Program Plan. Five-Year Accident History One accident, as described under 40 CFR 68.42(a), has occurred at the Ashland WTF in the previous five years. This accident was due to human error, and resulted in only minor injury for one employee. As a result of the accident, employee training has been revised to prevent repeat of this accident. Emergency Response Program The emergency response program established by the City of Lincoln fo r the Ashland WTF does not require personnel to respond to accidental releases of regulated substances. The local emergency response agencies will be relied upon for coordinating all response actions resulting from the release and for informing the public about the release. The facility has developed an Emergency Action Plan outlining actions taken in the event of an accidental release of regulated substances as well as in the event of natural disasters. Safety Improvements The facility is currently in the process of evaluating the recommendations from the process hazard review completed in February 1999. Any improvements made in response to the recommendations will be documented. |