Elizabeth City Water Treatment Facility - Executive Summary |
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The Elizabeth City Water Treatment Facility uses a lime softening treatment process. Raw water is pumped from the Wellfield to a three (3) million-gallon reservoir located on the facility site. From there the water is pumped via a booster pump to the head of the facility where the water is aerated to strip out the carbon dioxide. The water then goes to the reactor clarifiers where Aluminum Sulfate and polymer is added to aid in the coagulation process. Hydrated lime is then introduced to raise the pH to 10.3 for softening purposes. As the pH is increased, hardness is precipitated out as Calcium Carbonate and Magnesium Hydroxide, which are mostly insoluble compounds. Water then enters the flocculation basin where it is recarbonated to lower the pH back down to an acceptable level. From there the water enters the sedimentation basins where the larger suspended particles are allowed to settle out; any remaining particles are filtered out through the dual media rapid sand filters. These fi lters are made up of twenty-one (21) inches of anthracite, nine (9) inches of filter sand and twelve (12) inches of support gravel. The facility has five filters with each having a design filtering capacity of one (1) MGD. Just prior to the filters, Sodium Hexametaphosphate is added for corrosion control. Hydrofluosilicic Acid is added to the finished water to help in the prevention of dental caries. A combination of Chlorine and Ammonia is introduced to the water for disinfection. The facility usually keeps 16,000 pounds of chlorine on site for this purpose. The finished product is stored in a three (3) MG and one (1) MG ground level clearwell on site. The distribution system has three (3) elevated storage tanks- one (1) at one (1) MG capacity and two (2) at one half (1/2) MG capacity. The UtilityTreatment Division of Public Works has adopted a Process Safety Program in order to implement 29 CFR 1910.119, the OSHA Standard Regulating Process Safety Management of Highly Hazardous Chem icals and to enable all those who may be affected to be able to identify and understand the hazards posed by the processes that involve those chemicals. This program will help prevent the occurrence of, or minimize the consequences of catastrophic releases by stating our policies and procedures for the management of process hazards in design, construction, start-up, operation, inspection and maintenance. Our program calls for maximum employee participation and includes all elements of the employee participation provisions of the OSHA standard. This program will be regularly reviewed and updated and whenever necessary to reflect new or modified tasks and procedures. The UtilityTreatment Divsion's emergency response program was developed to comply with OSHA standards 29 CFR 1910.38, 1910.120 and to ensure the safety of employees and the public. It shall be used in all emergency situations which may occur at the Water Treatment Facility. Generally this program shall cover emergencies suc h as fire, medical emergencies, accidents, catastrophe's, toxic releases like equipment malfunctions resulting in the real or potential release of chlorine and other emergency situations requiring the orderly evacuation of this facility and/or activation of our Division HAZMAT Team. In the event of public evacuation the division shall team with the Pasquotank/Camden/City LEPC for further assistance. To fully understand the impact of releases at the facility a worst-case release and alternative release scenarios were performed utilizing the EPA's RMP COMP (TM). The worst-case models the release of 2000 pounds of chlorine gas at 110 pounds per minute for a duration of 10 minutes. The release will occur in an enclosed space, in direct contact with outside air. The distance to the endpoint for the worst-case scenario is 0.9 miles. Estimated residential population within distance to endpoint is 1300. This release would extend beyond the facility boundary. The alternative release models the release of 762 pounds of chlorine gas at 12.7 pounds per minute for a duration of 60 minutes.The distance to the endpoint for the alternative scenario is less than 0.1 mile. Estimated non-residential population within distance to endpoint is 25. This release will occur in an enclosed space, in direct contact with outside air. This release has the possibility of extending beyond the facility boundary. This facility has had no reportable accidental releases of chlorine in the last five years. The facility was originally constructed in 1926 and has had several modernizations and upgrades. The last major upgrade was undertaken in 1997-1999 by Arcadis, an engineering firm in Raleigh. Several process changes were made as well as the construction of a new chemical building to house the chlorine along with the installation of new chlorinators, injectors, scales, piping, valves and safety equipment necessary to provide a complete remote vacuum type chlorine feed system. The chlorine leak det ector is in the chlorine storage and feed room. Adjacent to the detector is a wall-mounted audible alarm powered through dry contacts in the detector unit. The unit is also equipped with dry contacts for the emergency exhaust fan and computer alarm in the main operations station. |