Billerica Water Treatment Plant - Executive Summary |
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Section 1 Risk Management Plan Elements Billerica Water Treatment Plan Town of Billerica, MA 1.1 Executive Summary The Town of Billerica Water Treatment Plant (WTP) accidental release prevention policy involves a consolidated approach that integrates technologies, procedures, and management practices. All applicable procedures of the U.S. Environmental Protection Agency (EPA) Prevention Program are followed. The WTP emergency response policy involves the preparation of response plans that are tailored to each facility and to the emergency response services available in the community, and meets the EPA Emergency Response Program requirements. The Town of Billerica WTP, located at 250 Boston Road, Billerica, Massachusetts, is required to provide disinfection of the treated water before its disc harge to the water distribution system. The Town presently utilizes chlorine gas for disinfection to meet the minimum standards of the Safe Drinking Water Act. Nine one-ton containers of pressurized liquid chlorine are located on site. Three one-ton containers of chlorine are located within the building of which two are manifolded to the chlorination system. The remaining six cylinders of chlorine are each stored in one-ton containers on an exterior elevated rack. The offsite consequence analysis includes consideration of two release scenarios, identified as "worst case release" and "alternative scenario." EPA defines the first scenario, 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 de termine the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint" selected by EPA of 3 ppm (chlorine), which is the Emergency Response Planning Guideline Level 2 (ERPG-2). The American Industrial Hygiene Association (AIHA) defines this 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 involves a failure of a one-ton storage tank containing either 2,000 pounds of chlorine. The offsite consequence analysis for these tanks was performed for two sets of conditions. The first set of conditions was pr edefined by the EPA. This analysis assumed that the vessel would completely release all of its contents in ten minutes. The toxic endpoint used was the one-hour average ERPG-2. The population residing within a full circle with a radius corresponding to the toxic endpoint distance was determined. For the worst-case modeling analysis, the EPA-mandated meteorological conditions were used. These correspond to Stability F, wind speed of 1.5 m/s, highest daily temperature of 77oF and an average humidity of 50%. From the modeling results, it was concluded that the radius which corresponded to the toxic endpoint distance was 3.0 miles. Within the 3.0 miles, approximately 46,800 people would be affected by this EPA-specified release and the corresponding conditions. The alternative release scenario involves the release of a one-ton cylinder of chlorine. In this case, however, the release is inside a building. The release is assumed to be over a ten-minute time period. Liquid chlorine released from the ruptured whip would flash immediately to a vapor. The meteorological conditions used were Stability D, wind speed 3.0 m/s, average air temperature of 50oF, and 50 percent average humidity. Based on these conditions, the off-site impact extends 0.6 miles. The chlorine detector is the active mitigation measure considered. The general WTP accidental release prevention program is based on the following critical elements: ~ High level of training of operators ~ Preventive maintenance program ~ Use of state-of-the-art process and safety equipment ~ Use of accurate and effective operating procedures, written with the participation of the operators ~ Performance of a hazard review of equipment and procedures ~ Implementation of an auditing and inspection program Chemical-specific preventions steps include availability of self-contained breathing apparatus (SCBA), awareness of the hazardous and toxic properties of chlorine, and presence of c hlorine detectors. No accidental releases of chlorine have occurred at this facility in the past five years. The facility has an emergency response program, which has been coordinated with the Billerica Fire Department. |