Valrico Advanced Wastewater Treatment Plant - 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 and manages a number of water and wastewater treatment facilities throughout unincorporated Hillsborough County, Florida. All applicable procedures of the United States Department of Environmental Protection, Florida Department of Community Affairs and Department of Environmental Protection are adhered to. The HCWD emergency response policy involves the preparation of response plans for each facility. Each facility is in compliance with the EPA emergency response program requirements. The Valrico Advanced Wastewater Treatment Plant (AWT) is located on 36 acres in the northwest portion of a 1,535-acre former phosphate mine in rural eastern Hillsborough County. In addition to the treatment plant, the complex includes wastewater transmission facilities, a rec laimed water system, a 263 acre on-site effluent sprayfield and surface water discharge facilities. Offisite Consequence Analysis: The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case 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 10 minutes," due to unspecified failure. The alternative scenario is identified as "more likely to occur than the worst case scenario." The HCWD used the EPA lookup tables to determine endpoints for its "worst case scenario" and "more likely scenario". The worst case scenario at Valrico AWT involves an unspecified failure of a one-ton container of chlorine which is stored as a liquid under pressure. This scenario was researched in the EPA lookup tables. The EPA set the conditions for the worst case scenario modeling and as sume the release of the entire amount of liquid as a gas in 10 minutes, use of the one-hour ERPG-2 as the toxic endpoint and consideration of the population residing within a full circle with radius corresponding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of 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 will flash to a vapor. The remaining liquid will form droplet aerosols. This aerosol results in a very dense chlorine cloud of vapor and liquid droplets, with dispersion characteristics significantly different than for a cloud of only chlorine gas. B. Only the population within an elliptical plume extending downwind of the releae point is potentially affected. The plume area, or footprint, is approximately six (6) percent of the full circle. EPa-mandated meterological conditions, Stability F, wind speed of 1.5m/second, highest daily maximum temperature and average humidty were used. Mitigation systems to be considered include the chlorine detetection system and the vacuum piping. The Valrico AWT chlorine system is a vacuum system. This system can be expected to significantly reduce the amount of chlorine released in case of a pigtail or piping failure. The general HCWD release prevention program is based on several key elements: High level of training of operators and maintenance staff Preventative maintenance program State of the art process and safety equipment Accurate, effective operating procedures Hazard review of equipment and procedures In-house inspection program Chemical specific prevention steps include availability of self-contained breathing apparatus (SCBA) worn by the operators during connection/disconnection of the chlorine and/or sulfur dioxide supply, awareness of hazardous and toxic properties of chlorine and sulfur dioxide and the presence of chlorine and sulfur dioxide detection equipment. The facility also maintains sulfur dioxde and chlorine repair kits on site |