Heart of the Valley Metropolitan Sewerage District - Executive Summary |
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The HOVMSD will provide wastewater treatment at a minimal cost by maintaining disinfection and dechlorination with chlorine and sulfur dioxide. This facility has no history of accidental releases. The hazards analysis conducted as part of this program has lead to safety improvements to the monorail used in ton cylinder unloading. An economic analysis for an equipment conversion for an alternative chemical (hypochlorite) would be $51,000 without interest or depreciation. The additional O&M costs for the more expensive hypochlorite reagent results in an additional $40,000 per year. Additional capital and operational costs would be incurred for a similiar conversion to liquid bi-sulfite for dechlorination. The zero accidental release history is a result of detailed handling procedures, training and established preventative maintenance practices. Periodic maintenance is scheduled by JOB CAL, a computer program or is obtained by outside contractors (see hazard analysis). The District's release prevention program rests on the scheduled maintenance for all equipment associated with chlorine and sulfur dioxide dispensing. Part of this effort is outsourced to Bailey-Fischer Porter. The emergency response policies are found in the off-site facility plan. This plan meets off-site planning guidance as established by SERB. The Heart of the Valley MSD facility is an advanced activated sludge plant using gaseous chlorine and sulfur dioxide for disinfection and dechlorination. The worst case scenario for chlorine involves the evacuation of a ton cylinder in ten minutes. This produces a release rate of 200 pounds per minute. The 1.33 mile urban endpoint distance was predicated on an atmospheric stability class F with a windspeed of 1.5 m/s. This result is based on a release outside. Cylinders and equipment are stored inside buildings, however, the intention of this scenario is to provide information on the worst case leak. For sulfur di oxide, the same conditions and considerations apply for the worst case scenario consideration. The largest container is a 150 pound cylinder. The release rate is 15 pounds per minute. The distance to the urban toxic endpoint is 0.31 miles. The chlorine alternative scenario relates release rates resulting from a liquid release through a quart inch diameter hole (corrosion hole). The release rate from this situation yields a value of 161 pounds per minute. The distance to the toxic endpoint for this urban release is 0.27 miles. The alternate scenario for sulfur dioxide is base on the three-sixteenth inch diameter opening in the vapor space of ta 150 pound cylinder. The valve of a 150 pound cylinder has a three sixteenth inch opening, which is, therefore the size of an opening should the valve be sheared off for any reason. The release rate is 3.1 pounds per minute. The distance to an urban toxic endpointpoint is 0.06 miles. Accidental releases result from an unspec ified sequence of actions. Handling procedures for chlorine and sulfur dioxide contain general precautions, loading/unloading considerations, procedures for placing bulk tanks on scale, connection/disconnection instructions plus emergency response procedures for uncontrollable releases accompanied with an emergency contact call list. The HOVMSD facility has had zero accidental releases of chlorine or sulfur dioxide in the past five years. There have consequently been zero on-site or off-site injuries. The employees at the facility have not been trained to respond to regulated substance releases. The scope of the response is contained in the EPCRA hazardous materials response plan. |