Northwest Regional Dechlorination Facility - Executive Summary |
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The Hillsborough County Water Department (HCWD) operates several water and wastewater treatment facilities within unincorporated Hillsborough County and practices an accidental release policy which integrates technology, established procedures and management practices in a unified approach to risk management. HCWD facilities comply with applicable policies and procedures of the United States Environmental Protection Agency, the Florida Department of Environmental Protection and the Florida Department of Community Affairs. The Facility The Northwest Regional Dechlorination Facility is located at 9320 West Waters Avenue, Tampa, Florida. The facility dechlorinates highly treated wastewater before it is discharged to surface waters. The removal of chlorine is vital to maintain the delicate environmental balance of Tampa Bay waters. Offsite Consequence Analysis The offsite consequence analysis includes consideration of two sulfur dioxide release scenarios, identified as "worst cas e release" and "alternative scenario". The first 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 ten minutes," due to unspecified failure. The alternative scenario is identified as "more likely to occur than the worst case scenario." The worst case scenario at Northwest Regional Dechlorination Facility involves the unspecified failure of a single ton container of sulfur dioxide. The EPA-specified conditions assume the release of the entire amount as a gas in ten minutes, use of the one hour ERPG-2 as the toxic endpoint and consideration of the population residing within a full circle with radius coresponding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis. The Water Department believes the EPA assumptions to be unrealistic because: A. Only a fraction of the compressed liquif ied sulfur dioxide released to the atmosphere flashes to a vapor. The remaining liquid forms liquid droplet aerosols. This results in the formation of a very dense sulfur dioxide cloud made up of vapor and liquid droplets, with dispersion characteristics very different than for a cloud of only sulfur dioxide 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 area of the full circle. EPA-mandated meterological conditons, Stability F, wind speed of 1.5 m/second, highest daily maximum temperature and average humidity were used for "worst case scenario". Mitigation systems to be considered at Northwest Regional Dechlorination Facility include a leak detection system with auto-dialer, vacuum piping and an enclosed chemical building. These could be expected to reduce the sulfur dioxide release effects by more than 55 percent. Release Preventi on Program The general Water Department release prevention program is based on several key elements: A. High level of training of operations and maintenance staff B. A strong 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 connection/ disconnection of the sulfur dioxide containers and awareness of the hazardous properties of sulfur dioxide. The facility is equipped with leak detection equipment and a leak repair kit. |