Northwest Regional Potable Water Facility - Executive Summary |
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The Hillsborough County Water Department (HCWD) has an accidental release prevention policy integrating technology, established procedures and management practices into a unified approach to risk management. The HCWD operates a number of water and wastewater treatment facilities throughout unincorporated Hillsborough County, Florida. Northwest Potable Water Facility The Northwest Potable Water Treatment Faclity is located at 12950 Fawnridge Road, Tampa, FL 33626. Offsite Consequence Analysis The offsite consequence analysis includes consideration of two chlorine release scenarios identified as "worst case release: and "alternative scenario". The worst case scenario is defined by the EPA, 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 identified as "more likely to occur". The worst case scenario at Northwest Potable Water Teratment Facility involves an unspecified failure of a single one-ton chlorine container. The offsite consequence analysis was determined utilizing the EPA lookup tables. The lookup tables follow a specific set of atmospheric and meterological conditions. Those conditions include Stability F, highest maximum daily temperature, average humidity and wind speed of 1.5 m/second. The EPA assumptions include dispersal of the entire ton as a gas in 10 minutes, use of the ERPG-2 as the toxic endpoint and consideration of the population residing within a full circle with the radius corresponding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis. The HCWD believes the EPA assumptions to be unrealistic because: A. Only a fraction of the compressed liquified chlorine released to the atmosphere flashes to a vapor. The remaining liquid forms liquid droplet aerosol. This results in the formation of a v ery dense chlorine cloud consisting of vapor and liquid droplets, with dispersion charateristics significantly different than for a cloud of only chlorine gas. B. Only the population within an elliptical plume extending downwind of the release point is potentially affected. The plume area, or footprint, is approximately six percent of the full circle. Mitigation systems to be considered include the chlorine leak detection system and vacuum piping. The vacuum system is expected to limit the amount of chlorine gas lost due to a pipe or pigtail failure. The general Water Department release prevention program is based on several key elements: A. A high level of training of operations and maintenance staff. B. Agressive preventative maintenance program C. State of the art process and safety equipment D. Accurate, effective operating procedures E. Hazard review of equipment and procedures F. An in-house inspection program Chemical specific prevention steps include the availability of self-contained breathing apparatus (SCBA) worn by the operators during connections / disconnections of the chlorine supply, a high level of awareness of the hazardous and toxic properties of chlorine and the presence of chlorine leak detection systems. The facility also maintains an approved chlorine repair kit. |