High Hill Chlorination Building - Executive Summary |
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Facility and Regulated Substance Handled The High Hill Chlorination Building is located on Faunce Corner Road in Dartmouth, Massachusetts adjacent to the High Hill Reservoir. High Hill Reservoir is a 67 million-gallon distribution storage facility that stores treated water from the Quittacas Water Treatment Plant. The High Hill Chlorination Building is a chlorine storage and feed facility that provides booster disinfection of water stored in the High Hill Reservoir prior to entering the water distribution system for the City of New Bedford and surrounding towns. Maintaining adequate levels of chlorine residual in the water distribution system is essential and is achieved through disinfection with chlorine, which is an EPA regulated substance. Four one-ton containers of chlorine (8,000 pounds) are present at the High Hill Chlorination Building which is in excess of the regulatory threshold and thus requires development of a Risk Management Program. Four one-ton containers of chl orine are present in the Scale Room which is comprised of two chlorine scales, each holding 2 one-ton cylinders, so that one scale can be in operation while the second is on standby. Chlorine gas is withdrawn from the on-line pair of cylinders and an automatic chlorine gas switchover system transfers gas flow from an exhausted source to a standby source to ensure continuous disinfection as required by Federal law. Chlorine gas from the ton containers is fed through the chlorine gas manifold to the chlorinators (two on-line and one standby) located in the adjacent Chlorinator Room. The chlorinators and accessories are designed to control the chlorine flow rate and to direct the gas flow to ejectors which combine the gas with water to form a chlorine solution for disinfection. Risk Management Program Development of the Risk Management Program for the High Hill Chlorination Building has served as an opportunity to evaluate operational and safety issues associated with the use of chlo rine. The Water Department has identified the Assistant Superintendent for providing overall leadership for the Risk Management Program and the Head Operator for providing maintenance of the program. Evaluation of risks from chlorine has involved inspecting existing facilities and compiling safety information for chlorine. This led to conducting a hazard review to identify deficiencies in equipment and operation which could be improved as part of the Risk Management Program. Planned Changes As a result of the hazard review, planned improvements include providing new self-contained breathing apparatuses and escape respirators, connecting the chlorine gas detector alarm with the Quittacas Water Treatment Plant by telemetry, installing ventilation for the scale room, installing a windsock, and installing an outdoor beacon and horn to serve as an alarm during emergency conditions. Compliance audits will be conducted by the Water Department every three years to evaluate the implement ation of the Risk Management Program. Incident investigation reports will be generated for any incident to track problems, eliminate potential recurrence of accidents, and provide a safe working environment for all employees. Accident History Over the past five years there has not been any reportable accidents involving chlorine. Prevention Program Preventative maintenance service is performed annually on all chlorination equipment by a qualified service technician to ensure that all equipment has been inspected, tested and calibrated. Preventative maintenance is a critical component of equipment maintenance and can serve to prevent accidental releases of chlorine resulting from equipment failure. In addition to the annual inspection plant operators perform routine maintenance service which serves to monitor the day-to-day operation of equipment and ensure proper performance. Additionally, the Department of Environmental Protection conducts on-site sanitary surveys of the Hig h Hill Chlorination Building facilities to inspect equipment and determine that operation and maintenance procedures are adequate and is able to produce and distribute safe drinking water. Standard operating procedures have been developed for all operating conditions involving chlorine to ensure uniform operation by all treatment plant operators. Treatment plant operators also receive on-the-job and classroom training in use of chlorination equipment. Outside courses have included "Handling Chlorine and Anhydrous Ammonia Emergencies" by Region One Regional Response Team in cooperation with the Massachusetts Emergency Management Agency, "Hazardous Materials Technical Level Training" by New England Water Works Association, and "Chlorine Safety and Handling Seminar" by Jones Chemicals. Worst-Case Release Scenario The worst-case release scenario was determined to be the complete release of chlorine from a single one-ton container. This represents the greatest amount held in a single vessel on-site. Since chlorine is a gas at ambient temperature it was assumed to be released over a period of ten minutes in accordance with the Risk Management Plan regulations. Because chlorine gas is denser than air, the SLAB computer model was used which was developed by the USAF Engineering and Services Center and the American Petroleum Institute to simulate atmospheric dispersion of denser-than-air gas releases. In accordance with EPA modeling requirements for worst case releases, a wind speed of 1.5 meters per second and atmospheric stability class of F were used in conjunction with rural topography surface roughness coefficients. The SLAB model determined that the maximum distance to a toxic endpoint of 3 parts per million of chlorine generated from the worst-case release scenario is 2.9 miles. While the actual impact area would depend on the prevailing wind direction, the potential impact area lies within a circle around the Chlorination Building with a radius of 2.9 mile s. This radius equates to an area of 26.4 square miles, and includes residential areas, schools, recreational areas, a prison, major commercial, office or industrial areas and churches. Alternative Release Scenario The alternative release scenario selected is a scenario for the accidental release of chlorine due to a failure of a one-inch schedule 80 PVC pipe connected to 2 one-ton cylinders. Since 2 one-ton cylinders are manifolded together and are on-line at all times, the potential for a leak drawing from two cylinders is a possible scenario. The total chlorine release estimated from this condition is 634 lbs over 27 minutes. (American Water Works Association Research Foundation, Compliance Guidance and Model Risk Management Program for Water Treatment Plants, 1998) Local meteorological conditions from the nearby New Bedford Airport were used for average daily temperature, humidity, wind speed and stability class. The SLAB model determined that the maximum distance to a t oxic endpoint of 3 parts per million of chlorine generated from this alternative release scenario is 0.3 miles. The alternative release scenario has a significantly smaller potential impact area of 0.28 square miles in which there are residences but there are not any schools, churches, prisons etc. Emergency Response Policies A mutual aid agreement was developed between the Dartmouth Fire Department and the New Bedford Fire Department to respond to notification of a chlorine release at the High Hill Chlorination Building. Since the Chlorination Facility is within Dartmouth but owned and operated by the City of New Bedford, it was determined that a mutual aid agreement would allow for a timely response and best use of available resources. The Dartmouth Fire Department and New Bedford Fire Department will both respond to notification of a chlorine release. The New Bedford Fire Department's HAZMAT team will be part of the response team. The Water Department submits Tier Two chemic al inventory reports to the Dartmouth Local Emergency Planning Committee (LEPC) in accordance with the Emergency Planning and Community Right-To-Know Act. This information is provided on an annual basis to enable the LEPC to account for all chemicals within its jurisdiction. The Water Department has made the Assistant Superintendent available to serve on the LEPC to ensure that the High Hill Chlorination Facility is properly represented. |