Spring Branch Wastewater Treatment Plant - Executive Summary |
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EXECUTIVE SUMMARY (Spring Branch Wastewater Treatment Plant) The accidental release prevention and emergency response policies at your facility: The City of Huntsville Water Pollution Control (WPC) Department's primary goal is to protect public health and the environment, and to continuously attempt to reduce the risks associated with the use of chemical substances. WPC follows the City of Huntsville's general safety policy of providing a safety program designed to safeguard all employees, and to minimize the frequency and severity of accidents. In addition to the City's general safety policy, WPC safety policy involves a combined commitment of both management and employees through continuous efforts in reducing/preventing hazardous conditions at all City of Huntsville Wastewater Treatment Plant (WWTP) facilities. The WPC emergency response policy includes an emergency action plan designed for non-responding facilities involving the coordination with local emergency responders (Fire D epartment-HazMat Unit) and local emergency planning committee (Huntsville-Madison County Emergency Planning Committee) to ensure, in the unlikely event of accidental release, the community and environment has an effective response strategy available. A description of your facility and the regulated substances handled: The Spring Branch Wastewater Treatment Plant (WWTP), located at 1800 Vermont Road, Huntsville, Alabama, is a 41 million-gallon per day (MGD) conventional activated sludge facility. Treatment processes include screening, grit removal, primary clarification, coarse bubble aeration, secondary clarification and chlorination. Sludge treatment and processing involves gravity thickening, anaerobic digestion and dewatering using sand-drying beds. The treated effluent is then discharged to the Tennessee River. The facility is manned by State certified wastewater treatment operators, twenty-four hours per day (three eight hour shifts) seven days per week. The regulated subst ances used at the Spring Branch WWTP are chlorine, propane and methane. The purpose for the chlorination process is for effluent disinfection and thus to prevent the spread of waterborne diseases. The maximum amount of chlorine on site is twelve (12) one-ton cylinders. Propane is used for winter heating and fueling the boilers. The boilers produce the heat for the sludge digesters in order to maintain optimum bacterial activity. The propane storage system consists of three 10,000-gallon tanks. Methane gas is the principal by-product of anaerobic sludge digestion. The methane gas produced is drawn from the digesters, scrubbed (cleaned), compressed and stored in a 97,000 cubic foot capacity sphere. The resulting 'purified' methane is used as fuel for the blower engines. These blower engines supply air (oxygen) to the wastewater necessary for the activated-sludge process. The worse-case and alternative release scenarios: The Offsite Consequence Analysis (OCA) was conducted by foll owing the guidance outlined in EPA's industry-specific, Risk Management Program Guidance for Wastewater Treatment Plants document, 40 CFR Part 68-Risk Management Programs document, and the consequence distances were estimated utilizing EPA's RMP*CompTM atmospheric dispersion modeling software. Toxics worst-case release: EPA predefined the assumptions used for this analysis. This release scenario involves the release of a one-ton chlorine cylinder (2000 lbs.) uniformly, over a 10-minute period, resulting in the greatest distance to a specified endpoint. Mitigating effects of the chlorine building are considered; i.e., the release rate from the building will be approximately 55 percent (building release-rate-multiplicative factor provided by EPA) less than if the release occurred outdoors. The estimated distance to the endpoint obtained using EPA's specified parameters is 0.9 miles from the release source. The resulting area extends offsite, and public receptors are within the distan ce to the endpoint. The estimated residential population potentially affected is approximately 20. Toxics alternative release: This scenario involves a release due to the uncoupling of a chlorine cylinder transfer hose. The resulting release takes place indoors (mitigation effects of the building are taken into account) for a period of 10-minutes at a release rate of 30 pounds per minute. Active mitigation measures are not considered. Other assumptions (meteorological conditions, release duration) are obtained from guidance provided by EPA. The estimated distance to the endpoint is 0.1 miles from the release source. The estimated residential population potentially affected is 0. Flammables worst-case release: EPA predefined the assumptions used for this analysis. This release scenario involves a 10,000 gallon propane tank when filled to the greatest amount allowed (80% capacity, 33,600 lbs.), resulting in a vapor cloud explosion. The estimated consequence distance to an overp ressure level of 1-psi using EPA's specified parameters is 0.3 miles from the release source. The resulting area extends offsite, and public receptors are within the consequence distance. The estimated residential population potentially affected is 0. Flammables alternative release: This release involves the failure of an unloading hose caused by a driver failing to remove the hoses between the storage tank and delivery vehicle before driving away. The result is a vapor cloud explosion of the released quantity. The active mitigation measures are assumed to function properly, limiting the released quantity (approximately 69 lbs.) to that contained in the hose. The estimated consequence distance to an overpressure level of 1-psi is 0.03 miles from the release source. The estimated residential population potentially affected is 0. The general accidental release prevention program and chemical-specific prevention steps: The City of Huntsville ensures the Spring Branch WWTP facility is designed in compliance with recognized and generally accepted good engineering practices. The facility is designed, built and operated in accordance with all applicable Federal, state and local industry-specific regulations, codes and standards. The equipment specifications (materials for construction, actual design and tolerances) of any equipment used to store or transfer a regulated substance are appropriate for the specific materials and operations for which it is used. Elements of WPC's accident prevention program include a preventative maintenance and routine equipment inspection program. An upgraded training program, which augments the current level of training received by operators and maintenance personnel, has also been instituted. In addition, each department within WPC conducts weekly safety meetings to further enhance WPC's commitment towards accident prevention and community protection. Five year accident history: The Spring Branch WWTP has had no accidental relea se of chlorine, propane or methane that resulted in deaths, injuries, or significant property damage onsite, or known offsite deaths, injuries, evacuations, sheltering in place, property damage or environmental damage. The emergency response program: In the event of an accidental release involving a regulated substance, WPC emergency response procedure is to notify the Huntsville Fire Department (HazMat Unit) and request that they respond to the emergency. To ensure that an effective response is available, appropriate mechanisms are in place to notify emergency responders when there is a need for a response. Furthermore, emergency response efforts have been coordinated with both, the Huntsville Fire Department and the Huntsville-Madison County Emergency Planning Committee, to include this facility in the local community emergency response plan (developed under the Emergency Planning and Community Right-to-Know Act, EPCRA) regarding a response to a potential release. This will help to ensure that, in the unlikely event of a regulated substance release, the community and environment has an effective emergency response strategy available. Planned changes to improve safety: Recommended actions to improve safety were identified in March 1999, when a hazard review was completed for the facility. These recommended actions have been evaluated and implemented as required. |