Mount Sterling Wastewater Treatment Plant - Executive Summary

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The Mt. Sterling Water and Sewer System (MSWSS) located in Mt. Sterling, Kentucky operates a publicly owned treatment works (POTW) for the City of Mt. Sterling.  Operations at the POTW include the storage and handling of certain chemicals which are potentially hazardous.  It is the policy of the MSWSS to adhere to all applicable Federal and state rules and regulations. Safety depends upon the manner in which hazardous chemicals are handled and with the safe handling procedures that we use and the training of our personnel.  For emergency response involving a release, MSWSS has made arrangements with local emergency responders and has developed procedures for notification of the local fire authority and notification of any potentially affected neighbors. 
MSWSS has determined that it is subject to the requirements of Part 68 due to the storage and use of Chlorine which it obtains in 1 ton cylinders.  The maximum inventory on site at any one time is 4000 lbs., which is above the Part 68  
regulatory threshold quantity of 2500 lbs.  Chlorine is used in used at the POTW in a disinfection process which is necessary in order to meet discharge limit requirements imposed under the Clean Water Act. 
MSWSS has developed its OCA using release and dispersion data for chlorine obtained from EPA's guidance document.  MSWSS considers its worse-case release scenario to be a release of the entire contents of a single chlorine cylinder, i.e 2000 lbs, within the chlorine storage area.  There are no passive mitigation systems in place at the POTW which would restrict a chlorine release rate.  The area within the vicinity of the POTW is urban, with several building and residences which will potentially impact the dispersion of a toxic release.  It is assumed that the release will take place at ground level.   
The release of chlorine from a vessel at the POTW is based on the assumptions that the cylinder is full and that the release of the entire contents will take place over 10 minutes.  
This would result in a release of chlorine at a rate of 200 lbs per minute.  Based on an atmospheric stability class F and a wind speed of 1.5 meters/Second, the distance to the toxic endpoint offsite would be 1.3 miles. 
The area within the 1.3 mile radius surrounding the POTW has an estimated population of 4000 persons, based on 1990 census data obtained from Landview.  The area within the potentially affected radius includes schools, residences, a hospital, recreational areas, and office/commercial buildings.  
MSWSS has chosen what it believes is a reasonable alternative release scenario which is based on a chlorine gas release through a 1 inch diameter hole.  The hole would be from the result of a puncture to the cylinder or a sheared valve.  The vapor chlorine release rate for a 1 inch hole was estimated using the EPA's guidance document table for vapor releases.  The estimated release rate through a 1 inch hole is 150 lbs/min.  Assuming a D atmospheric stability with a wind spe 
ed of 3 meters per second and an urban topography, the distance to the off-site endpoint would be a 0.2 mile radius.  The area within the endpoint radius includes residences and office/commercial buildings. 
The MSWSS POTW facility complies with EPA's Accidental Release Prevention Rule and with all applicable state codes and regulations.  All employees are routinely trained in safety procedures related to the use and handling of chlorine. 
There have been no accidental releases involving chlorine at the POTW within the last 5 years. 
MSWSS has coordinated with local emergency responders to provide all necessary emergency response should a release occur.  Employees at the POTW are trained to evacuate to a place of safety and notify the local responders.
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