West River Water Treatment Plant - Executive Summary |
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WEST RIVER WATER TREATMENT PLANT The West River Water Treatment Plant (West River) has two independent chlorine injection systems that are fed through one ton container. There is only one ton container on line at any given time. The system is operated under vacuum using gaseous chlorine. There is a vacuum regulator to automatically switch from one injection system to the other when the pressure drops and the gas container is empty. Each one ton container is equipped with a spring loaded normally closed valve attached to the container head. If the system loses vacuum (due to a down stream malfunction, leak, etc.), the valve shuts and chlorine addition is automatically stopped. The valve is a normally closed, static control device that requires no electrical power to operate. The facility has three chlorine detectors to monitor leakage in the chlorine storage and chlorinator rooms. One detector in the chlorine storage room gives a digital readout of the atmospheric chlorine conc entration. The sensor is located in the storage room but the readout is located outside this area. Chlorine sensors are located at six inches above floor level in both rooms. The detector will alarm at the main control room panel and automatically start the dry scrubber in the affected area. Currently the facility has two building exhaust fans to vent the chlorine gas from the buildings and to provide a minor level of workers safety. A dry scrubber system is installed and operational. The gas inside the building is drawn into the scrubber and neutralized using a solid adsorbent. The scrubber has the capacity to adsorb one full ton container of chlorine gas (2000 pounds of chlorine). The West River Facility normally stores a maximum of ten one ton containers at the site at any one time. All containers are stored indoors in a building with doors, which seal. During chlorine deliveries, the delivery truck backs up to the unloading area. The building doors are open and the chlor ine containers are brought inside. Normally the chlorine storage and chlorinator rooms are sealed with doors that remain closed unless chlorine is being unloaded. All chlorine containers are stored within the chlorine storage room. If a chlorine leak is detected, the chlorine alarm will sound and the dry scrubber starts-up automatically. Air inside the building is evacuated and fresh air is drawn into the building. The scrubber will provide a negative pressure within the building and not allow the chlorine gas to leak outside A second safety feature in operation at this facility is vacuum regulator units. These units are installed on the operating and standby containers. If the valve loses vacuum because of a down stream leak on the vacuum side of the valve, the system will lose vacuum and automatically shut down. The facility also has an emergency response team with the proper training and equipment to deal with chlorine releases. The Worst Case chlorine release for this fac ility assumes that a one ton chlorine container ruptures during unloading outdoors in a rural area. The container discharges a dense gas release under worst case meteorological conditions of F Stability and 1.5 meters per second. All two thousand pounds contained in the ton container are assumed released over ten (10) minutes. It is only presented for comparative purposes and for non-OSHA facilities to determine under which RMP Program Level the facility fits. The Worst Case Impact Area is three (3) miles in radius (EPA CEPP Risk Management Program Guidance For Wastewater Treatment Plants EPA 550-B-98-010 October 1998). There are about 29,000 people living in the Worst Case release area who could be affected by this release. Located within this area are ten schools. They are Amity High School, Center School, Wintergreen School, Brennan School, Helen Street School, Blessed Sacrament School, Church Street School, Dunbar Hill School, Bear Path School, and the Eli Whitney Technical School. Also in this area are seven cemeteries, Mount Sacred Heart Convent, and recreational areas and parks. The Most Likely release case is that no chlorine will be released outside of the clorinator building. As indicated above there are three redundant levels of safety controls at the facility should a release occur. First the dry scrubbing system would prevent any released chlorine gas from exiting the building. Second, the vacuum regulator check unit would shut down and prevent additional gas from being released from the container. Thirdly, an alarm would be sounded and the facilities emergency response team would be at the location within a few minutes to shut the system down if all of the automatic controls failed. In order to evaluate a Most Likely release scenario that results in a release that is not contained, it is necessary to assume that all automatic controls fail and the on-site response team must shut off the leaking chlorine container. Under those unlikely as sumptions, the following release scenario was addressed. A steady-state leak of up to 5 pounds per minute of chlorine either as a gaseous or a two-phase release. It should be noted that a completely filled one-ton container has a maximum gaseous discharge rate of about 500 pounds per day ( 0.35 pounds per minute). Significant gaseous discharges above this rate will result in the container freezing up and the discharge stopped. It is also assumed that the container discharges a dense gas release under meteorological conditions of D Stability and 3.0 meters per second at an ambient temperature of 25 C. The Most Likely Case Impact Area is a tenth (0.1) of a mile in radius (EPA CEPP Risk Management Program Guidance For Wastewater Treatment Plants EPA 550-B-98-010 October 1998). There are about 15 people living in the Most Likely Case release area who could be affected by this release. The impact area may affect a small portion of Lake Dawson. Otherwise, there are no schools, hospita ls, parks or other sensitive receptors located within this area. In fact almost all of this release would be contained on the South Central Connecticut Regional Water Authority property. The facility has not had any accidental releases of chlorine from this covered process in the five years prior to the submission of this Risk Management Plan (RMP). |