City of Thomson - Big Creek Water Treatment Plant - Executive Summary
The City of Thomson has completed a Risk Management Plan consistent with Section 112 (r)(7) of the Clean Air Act and Part 68 of Volume 40 of the Code of Federal Regulations. These procedures seek to provide for employee safety, public health, and response agency interaction with respect to the disinfection process. |
The City of Thomson Big Creek Water Plant withdraws raw water from Clark Hill Lake (J. Strom Thurmond Lake). Finished water from the plant is disinfected with chlorine and is distributed to residents and numerous industries in the City of Thomson and McDuffie County. The chlorination process includes one-ton chlorine cylinders, chlorination equipment, electrical equipment, and a chlorine gas detection system.
Modeling was performed using RMP*Comp for both the worst case and alternative scenario to determine the potential consequences associated with an accidental chlorine gas release. For each case, atmospheric dispersion modeling was used to determine the distance trav
eled by the chlorine gas before its concentration decreases to a theoretical "toxic endpoint".
The worst case scenario involves failure of a one-ton cylinder yielding a cumulative release of 2,000 pounds of chlorine over a duration of ten minutes. The distance to "toxic endpoint" was 1.3 miles. The alternative (more likely) scenario involves mechanical failure of one flexible manifold connection (pigtail) allowing an unnoticed release to occur through this hole for one hour. The distance to "toxic endpoint" under this alternative was 0.1 miles. In support of the probability that a worst case scenario is not likely to occur, a review of process history indicates that no reportable accidental releases (greater than ten pounds) has occurred in the past five years at the Big Creek plant. While the City remains vigilant to chlorine hazards and the reduction of any such hazards, currently there are no major plans to improve safety at the plant.
The following key elements are include
d in the City of Thomson's RMP: operator training, preventative maintenance program, chlorine gas detection equipment, standard operating procedures, hazard review of equipment and operating procedures, compliance auditing, and operator training.
The Big Creek plant has an emergency response plan in conjunction with the Thomson Fire Department and McDuffie County Emergency Management Agency. Emergency response drills, drill evaluations, and facility tours are operated annually at which time emergency operation and response training procedures are also reviewed. Joint training sessions with the Fire Department are also used to provide a forum for maintaining effective chlorine handling procedures and timely emergency response to potential chlorine hazards.