Shenandoah Water Treatment Plant - Executive Summary |
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The Municipal Authority of the Borough of Shenandoah (MABS) operates a Water Treatment Plant (WTP) located in West Mahanoy Township, Schuylkill County, Pennsylvania. The WTP utilizes the toxic chemical, chlorine, for disinfection during the treatment process. Chlorine is stored in quantities which exceed the process threshold defined in 40 CFR Part 68. This regulation defines the requirements for the MABS Risk Management Program, including this document, the Risk Management Plan. The MABS WTP was constructed in 1994 and became operational in 1995. The facility has used chlorine, stored in one (1) ton cylinders, since its inception. The maximum amount of chlorine stored on site is four (4) one-ton cylinders. The facility operates 24 hours per day and is manned by at least one water treatment plant operator during two (2) shifts. The plant utilizes an automatic dialer system for notification and response during the unmanned shift. The chlorine cylinders are stored in an enclosed room, constructed of concrete block. The chlorine injection system has been designed to incorporate numerous safety features to prevent, detect and respond to leaks. The Risk Management Program included two (2) scenerios for the offsite consequence analysis, identified as "worst-case release" and "alternative release" scenario. The worst-case scenario as defined by EPA, states that "the owner or operator shall analyze 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 was performed to determine the distance traveled by the toxic liquid released before its concentration decreases to the "toxic endpoint". The endpoint concentration is defined by the EPA as a concentration that can result in significant public health impacts. The endpoints for toxic chemicals, as defined in 40 CFR 68.22, are based on the ERPG-2 concentrations developed by the American Industrial Hygiene Association (AIHA). The ERPG-2 level of concern is defined as "the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual's ability to take protective action." The toxic endpoint selected by EPA is 3 parts per million (ppm) (0.0087 mg/l) for chlorine. EPA's RMP*Comp program was used to complete the consequence analyses required under the Risk Management Planning Rule. RMP*Comp was developed by the CAMEO Team at the Office of Response and Restoration, National Ocean Service, NOAA, and the Chemical Emergency Prevention and Preparedness Office of the EPA. This program uses fixed values for certain atmospheric parameters, and does not allow them to be set by the user. This is because the software is i ntended as a simplified model, adhering to the EPA's Offsite Consequence Analysis Guidance, that is acceptable for compliance with the RMP Rule. Worst-Case Release Scenario: As required by RMP regulations, the worst-case release scenarios for the regulated substance involve the following: failure of a one-ton cylinder of chlorine over a ten minute period. In using the RMP*Comp program for the worst-case scenario for chlorine, a distance to toxic endpoint was established at 0.9 miles. In using the toxic endpoint distance of 0.9 miles, an estimated residential population of 600 would be affected. There were also public and environmental receptors identified. Alternative Release Scenario: The rationale for selection of the alternative release scenario used for chlorine was based on typical storage and use systems found at water treatment plants. These scenarios were developed by the American Water Works Association (AWWA). The alternative release scenario used for chlorine inv olves the rupture of the gas feed line. The amount of chlorine released was calculated at 23.4 ppm with a duration of 27.1 minutes. Toxic endpoint distances to ERPG-2 was obtained. Due to urban surroundings in the immediate area and the cylinders being in an enclosed space, the toxic endpoint was established at 0.1 miles. The general MABS emergency response program is based on the following key elements: (1) Personnel training (2) Preventive maintenance program (3) Use of state-of-the-art process and safety equipment (4) Performance of a hazard review of equipment and procedures (5) Implementation of an auditing and inspection program. There has never been an accidental release of chlorine at this facility. The facility maintains an off-site emergency response plan, which has been coordinated and approved by the Schuylkill County Emergency Management Agency. This plan includes planning and prevention procedures, hazard analysis, internal response capabilities, externa l resources, responsibilities, notification and reporting procedures. |