Dry Creek Wastewater Treatment Plant - Executive Summary |
|
1. Accidental Release Prevention and Emergency Response Policies This facility handles chlorine and sulfur dioxide, which are considered hazardous materials. The properties of both materials make it necessary to observe safety precautions in handling to prevent human exposure and to reduce the threat to the facility's workers and nearby members of the community. It is the facility's policy to adhere to all applicable Federal and State of California rules and regulations. Safety depends upon the safe procedures used to handle chlorine and sulfur dioxide; the safety devices and systems designed and constructed into the facility; and the training of the pertinent personnel. 2. Stationary Source and Regulated Substances Handled The facility treats wastewater discharged by residential, municipal and industrial users. This water is disinfected by mixing chlorine gas with the wastewater. Liquid chlorine is stored on site in one of the two 60-ton bulk storage tanks located in the Chlor ine Storage Building. One storage tank is kept empty to accept emergency chlorine transfer from the operating tank. Chlorine gas from the on-line container is piped into the chlorinators at several locations within the facility: 1) to the plant effluent at two locations, the East Roseville influent junction box and the North Roseville headworks, for ordor control; 2) to the return activated sludge to control filamentous growth; 3) at the secondary clarifier weirs for algae growth control; 4) to the filters to control algae growth; and 5) at two locations in the chlorine contact tank to disinfect either Title 22 or non-Title 22 water. The excess chlorine residual is dechlorinated prior to discharge using sulfur dioxide. Liquid sulfur dioxide is stored in one of the two 20-ton steel bulk storage tanks situated in the Sulfur Dioxide Storage Building. One storage tank is kept empty to accept emergency sulfur dioxide transfer from the operating tank. Each bulk storage tank has a liq uid withdrawal pipe connected to the sulfur dioxide evaporators; a gas withdrawal pipe connected to both the manual and electric vacuum regulator-check units; an air padding/vapor recovery pipe connected to the air padding compressed air system and to the truck unloading station; and a fill pipe connected to the truck unloading station. Sulfur dioxide gas can be released from the bulk tank to two sulfonators where the gas is monitored and drawn by vacuum to five injectors. One of the sulfonators is standby; the other regulates the flow of sulfur dioxide gas (under vacuum) to a remote injector on the effluent line. From the injectors, sulfur dioxide solution is routed to its point of use. 3a. Worst Case Release Scenario The 60-ton container of chlorine is the largest vessel in the chlorine feed system. Failure of this container will release 120,000 pounds of chlorine. It is assumed that the chlorine gas would be released at the rate of 12,000 lbs per minute for 10 minutes. The 60-ton container is stored inside of a building but the assumption is made that the gas release from the 60-ton container is directly to the surrounding atmosphere external to the building. The distance to the endpoint of 3 ppm for the Worst Case scenario extends beyond the boundaries of the stationary source. 3b. Alternative Release Scenario The Alternative Release scenario for both the 60-ton container of chlorine and the 20-ton container of sulfur dioxide is the failure of the plant operator to properly connect the hose to the pump truck during loading of the container and/or failure of the truck or plant operator to properly close the fill values prior to disconnect. The result, for both regulated substances, is a release of the chemical from the fill pipes or hose into the containment sump. The Alternative Release scenario for the bulk chlorine container is estimated at 472 lb/min for 5 minutes. The release rate for the Alternative Release scenario for the bulk sulfur diox ide container is estimated at 412 lb/min for 5 minutes. The distance to the endpoint of 3 ppm for the Alternative Release scenario for both chlorine and sulfur dioxide extends beyond the bounderies of the stationary source. 3c. Administrative Controls Administrative controls to limit the distances for each reported scenario exists to restrict to a minimum the amount of chlorine and sulfur dioxide released, if a release were to occur, and preferably to not have a release occur. This administrative control is inherent in the operational procedures for the chlorine and sulfur dioxide systems and the training provided to the chlorine and sulfur dioxide operators. 3d. Mitigation Measures Mitigation measures to limit the distances for each reported scenario exists to restrict to a minimum the amount of chlorine and sulfur dioxide released, if a release were to occur, and preferably to not have a release occur. The mitigation measures are based upon the design, inspection, testing, an d maintenance of the chlorine system and its related equipment and components. 4. General Accidental Release Prevention Program and Chemical Specific Prevention Steps The facility complies with all applicable federal and state codes and regulations. There are safety meetings and safety training. The Process Safety Management (PSM) program implemented at the facility for the chlorine and sulfur dioxide related activities and equipment represents one of the facility's main active commitments to an accidental release prevention program. 5. Five Year Accident History There have been no incidents involving the release of chlorine or sulfur dioxide within the past five years at the facility. 6. Emergency Response Program The Emergency Response Program is based on alerting personnel at the facility of the need to evacuate the facility and await the arrival of responders from the City of Roseville Fire Department at the evacuation assembly location if a release occurs that causes the evacuation to be initiated. The Placer County Office of Emergency Services can incorporate this response into the County Area Plan for the Region 4 Local Emergency Planning Commission. 7. Planned Changes to Improve Safety There are commitments made under the State of California's Risk Management Prevention Program (RMPP) that are being implemented at this time for the next year. Current applicable codes and regulations are being reviewed to determine if other commitments need to be made to achieve increased operational safety for the chlorine and sulfur dioxide systems. |