Henry County Water Company Water Treatment Plant - Executive Summary |
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Henry County Water Company Treatment Plant Chlorination Process Facility and Process Description The Henry County Water Company Treatment Plant serves the City of Clinton, Missouri and is operated under contract by Alliance Water Resources. Chlorine is stored at the Plant in ton containers that are co-located in a chlorine room. Chlorine is used at the Treatment Plant to disinfect the City of Clinton's potable water supply. The Plant's chlorine room is located within the general plant building. The treatment plant was recently constructed and placed into operation in March 1999. Approximately 60 lbs. per day chlorine is fed per day. The primary process component is the Wallace and Tiernan V-10 chlorination system, which meters and controls chlorine gas from ton-containers stored in the chlorine room. The chlorination system consists of two container-mounted vacuum regulators, two master gas feeders and two remote water injectors. The water injectors create a vacuum, accept the flow of gas, mix it with water and deliver chlorine solution to the water supply. The system is designed so that chlorine gas is removed from the ton-containers only under vacuum. If vacuum is lost, such as what might occur during a gas tubing break or disconnection, the vacuum regulator valve would shut-off chlorine feed and prevent release of chlorine gas. This system design greatly reduces the potential for accidental release of chlorine gas. Worst-case Release Scenario The Worst-case Release Scenario was assumed to be the release of an entire ton-container stored in the chlorine container room. In the scenario, the cause of the leak would be a container valve that would be inadvertently open when the outlet cap is removed. The assumed released quantity was 2,000 lbs. of chlorine, released in a period of ten minutes. RMPComp, 1.06 was the model used to calculate the affected area of the release. Data inputs used in the model were a relative humidity of 50%, ambient temper ature of 77 degrees Fahrenheit, chlorine temperature of 77 degrees before release, rural surface roughness coefficient, wind speed of 1.5 meters per second and an atmospheric stability of Class F. The release would occur at ground level inside the chlorine building and all receptors are considered to be at ground level. The toxic endpoint for chlorine gas as given in 40 CFR, Part 68.22 is 0.0087 mg/L. The distance from the scenario point of release to the toxic endpoint was calculated at 2.2 miles. The area located within a 2.2-mile radius of the process includes: 1) Most of the City of Clinton 2) State Wildlife Management Area 3) S. Grand River/Truman Reservoir To avoid the worst-case scenario, operators follow procedures to assure that container valves are closed before removing the outlet caps. As a backup safety measure, outlet caps are removed slowly to assure that the closed container valve is not leaking. If there is evidence of a leak, the cap can be tightened to s top the leak. Alternative Release Scenario The alternative scenario selected was a release of residual chlorine gas from a container assumed to be empty. The container valve would have been loosened from opening and closing during use and therefore may have the potential for leaking at the packing gland. RMPComp, 1.06 was the model used to calculate the affected area of the release. Data inputs used in the model were a relative humidity of 50%, ambient temperature of 77 degrees Fahrenheit, chlorine temperature of 77 degrees before release, rural surface roughness coefficient, wind speed of 1.5 meters per second and an atmospheric stability of Class F. The release would occur at ground level inside the chlorine building and all receptors are considered to be at ground level. In the scenario, the accuracy of one of the container scales would have drifted to show an empty container when actually up to ten pounds of chlorine remained in the container. The release of ten pounds of c hlorine would impact a radius of 0.1 miles. The affected area includes approximately four residences. To prevent the alternative release scenario from occurring, container scale accuracy is checked routinely. Also, loose packing nuts are tightened to reduce the potential for leakage. Accidental Release Prevention Plan In accordance with OSHA regulations, a Process Safety Management program has been established for the chlorine process. The program includes preventive measures to prevent releases. These measures include process safety information, procedures, process hazard analysis, training, mechanical integrity, management of change, employee participation, pre-startup reviews, hot work permits, contractor safety, incident investigation and compliance audits. Five-year Accident History There have been no significant chlorine releases at the facility. Emergency Response Program The facility is considered a "non-responding facility" and is included with the Emergency Respo nse Plan established by the City of Clinton Fire Departmen and the Henry County Emergency Planning Committee. |