EASTSIDE UTILITY WATER TREATMENT PLANT (WTP) - Executive Summary

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A.  The accidental release prevention policy of the Eastside Utility Water Treatment Plant (WTP) integrates technologies, procedures, and management practices.  To the best of our knowledge, all applicable U.S. Environmental Proctection Agency (EPA) procedures are adhered to.  The emergency response policy involves the application of tested techniques along with the initiation of the local emergency response teams' actions. 
 
B.  The conventional filtration process performed at the WTP facilitates the need for a substantial amount of chlorine.  Typically there are three one-ton cylinders of the chemical stored in a building designed specifically for such activity.  Along with the cylinders, the building houses various safety equipment, valves, hoses, scales, and chlorine alarms that notify the operator in a separate location in the event of a release.  There is an operator at the WTP at all times. 
 
C.  The offsite consequence analysis includes the examination of two chlorine release sce 
narios.  The first situation in the "worst case scenario" and the second is the "alternative scenario."  In the former case, the amount of chlorine gas in the single, largest container is released in the span of ten minutes.  While the latter is defined as the more likely occurence which, in Eastside's case, is the escape of gas via a faulty valve when a cylinder is being brought on line.   
 
A one-ton release of chlorine to the atmosphere is the setting of the worst case scenario.  This could actually occur as the cylinders are unloaded from a flat bed truck and into the chlorine building using a hoist.  If one of the vessels were to somehow become dislodged, it could strike the concrete surface of either the loading dock or the drive and rupture. 
 
The more likely release scenario of chlorine at the Eastside WTP stems from the fact that each cylinder must be brought on line when the scales indicate that another one is nearly empty.  A release to the atmosphere of the building could occ 
ur if a defective valve is encountered in the connection to the cylinder itself.  The resulting gas would escape through a .75 inch hole which corresponds to the diameter of the opening to which the transfer apparatus is connected.  Mr. Green estimates that the time from leak detection to the installation of the repair device would be ten minutes. 
 
RMP Comp was used to model both releases.  It used the toxic endpoint of 0.0087 mg/L and provided an estimated distance, in the form of a radius, to the endpoint.  This radius was plotted on both a United States Geological Survey map as well as a 1990 United States Census map, the latest available information of such a form.  The affected population was determined by counting the number of houses in each census tract and multiplying those counts by the average number of people in each.  An estimate was also included for the number of persons in the businesses within the affected area. 
 
Modeling for the worst case scenario entailed the ten-mi 
nute release of one ton of chlorine.  It yielded an estimated distance to toxic endpoint of 1.3 miles.  This was done using meteorological conditions of an F stability class, wind speed of 1.5 m/s (3.4 mph) and a temperature of 77 degrees F.  An estimate of population potentially affected was 2500.  An abscence of any mitigation was necessary for this model as the loading dock is not contained in a building. 
 
The alternative release scenario is defined as occurring inside the chlorine building that vents to the atmosphere.  This warrants a model with active mitigation.  The meteorological conditions were a Stabiltiy class of D, wind speed of 3 m/s (6.7 mph) and a temperature of 77 degrees F.  The results were a distance to toxic endpoint of 0.1 mile.  There are no structures within this distance except for the WTP itself.  As a result, the affected population would only be the Eastside employees present, which is an average of three.  (Note:  The estimated distance to the toxic endpoin 
t seems to be independent of the duration of the leak.  RMP Comp yielded a distance of 0.1 mile regardless of the time it took to correct the leak.) 
 
D.  The general WTP accidental release provention program is based on the following key elements: 
           High level of training of the operators 
           Preventive maintenance program 
           Use of state-of-the-art process and safety equipment 
           Use of accurate and effective operating procedures, written with the participation of the operators 
           Performance of a hazard review of equipment and procedures 
           Implementation of an auditing and inspection program 
Chemical-specific prevention steps include availibility of self-contained breathing apparatus, awareness of the hazardous and toxic properties of chlorine, and presence of chlorine detectors. 
 
E.  No accidental releases of chlorine have occurred at the facility in the past five years. 
 
F.  The Eastside Utility Water Treatment Plant has an eme 
rgency program, which has been coordinated with the Chattanooga Fire Department.  This program includes an emergency response decision tree and a notification plan. 
 
G.  The main change to improve safety is the acquisition of additional air tanks for the self-contained breathing apparatus present at the WTP.  This would provide further back-up in the event that a tank did not work properly or could provide additional time, if needed, to repair a leaking valve.
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