River Road Plant Chlorination and De-Chlorination - Executive Summary |
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Stony Brook Regional Sewerage Authority (SBRSA) stores and uses both chlorine and sulfur dioxide at its River Road wastewater treatment plant to provide disinfection and subsequent dechlorination of its effluent. A full program of accidental release prevention has been implemented which includes risk analysis and state of the art process safety techniques and alarms as well as standard operating and preventive maintenance procedures. SBRSA employees working in the EHS area are equipped with SCBAs, to enable them to effectively respond in any emergency situation that is less than IDLH, prior to mitigation by outside responders. The RMP* Comp dispersion analysis software provided by US EPA was used to model both worst case and alternate case releases. The worst case release scenarios were modelled as the release of either a full ton container of chlorine or sulfur dioxide within the container storage room. Assuming a 10 minute release time and using EPA's release-rate multiplicative fa ctor of 55%, the offsite impact would extend to 2.2 miles surrounding the facility for a chlorine release, and 2.1 miles surrounding the facility for a sulfur dioxide release. For an alternative release scenario of a chlorine or sulfur dioxide leak from the piping connecting the containers to the evaporators, a toxic endpoint of 1.3 miles has been modelled for chlorine and 0.8 miles for sulfur dioxide. The offsite impact of these releases has been minimized by housing the containers and evaporators within a sealed structure. Smoke testing has indicated that leaks can be contained within the building structure and released at a minimal rate through the use of an exhaust fan. Low level chemical specific leak detectors are installed to give early warning of minor leaks and enable SBRSA to respond and prevent significant accidental releases. In addition, process engineering safety controls and warnings alarms are in effect to prevent overpressurization or process operation outside accepta ble operating parameters. No accidents (as defined in 40 CFR 68.42) have occurred within the last five years. SBRSA's Emergency Response Program includes an Emergency Response Plan and emergency response training, which incorporates full site leak mitigation and evacuation drills. An audit of the program components has been performed annually to ensure compliance. In order to minimize offsite impacts and increase safety, SBRSA has plans to replace the use of chlorine and sulfur dioxide with an alternative disinfection process. The replacement is expected to be completed by the end of the year 2000. |