City of Lorain, Black River Treatment Plant - Executive Summary |
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City of Lorain, Ohio, Black River Treatment Plant 6/7/99 Risk Management Plan Executive Summary The Black River Sewage Treatment Plant is located on the east side of the mouth of the Black River. Lake Erie is immediately to the Northwest. Sewage is received from the central west side, east and south sides of Lorain, as well as from Sheffield Lake to the East. The plant is manned by two Operators 24 hours per day. Additionally, a maintenance crew and administrative staff are on hand during normal workdays between 7:00 AM and 4:00 PM. Chlorine is the chosen method of disinfection at the plant, and is fed from ton cylinders located on two scales in the chlorine room. Each scale holds two 1-ton cylinders. This room is located just 80 feet beyond the main entrance. Extra full cylinders are stored outside, just behind this room. Up to four cylinders may be in-use and feeding at a time, primarily dur ing the summer months. At other times, no more than two cylinders are in use. Up to 6 additional full cylinders may be on hand outside the chlorine room. Gaseous chlorine is fed from the top valves each pair of cylinders into a vacuum chlorinator and injected into a PVC pipe water stream, forming a strong hypochlorite solution. It is this solution that is fed to other points in the plant as a disinfectant. Since chlorine is pulled from the tanks under a vacuum, there is no risk of a raw chlorine leak beyond the tank valves. Accidental releases are limited by the vacuum chlorine system. Should a leak occur in the system between the tank and chlorinator, air would be drawn into the leak rather than chlorine leaking out, as the system is under vacuum at this point. A large rupture here would cause the vacuum operated valve on the tank to close immediately. Once a cylinder is in service, the main risk of any leakage is at the main valve and fittings connecting the feed system to the tank. A chlorine leak sensor is mounted within several feet of the tanks, and produces a loud, shrill alarm should chlorine be detected. Should a leak occur, operators are trained in the use of the Scott Air-Pak and B-Kit for stopping leaks. If a chlorine leak is detected, both operators don the Air-Paks. One Operator enters the room to deal with the leak, while the other waits just outside and watches, assisting only if necessary. Should the leak be such that it cannot readily be stopped, the fire department is notified for assistance and evacuation, as needed. Fire personnel are trained in the use of the B-Kit. The worst-case scenario would be a rupture to the cylinder tank itself, allowing the entire tank contents, 2000 lb., to spill out in a matter of minutes. If this were to occur to a cylinder outside the chlorine room, the area of vulnerability is 1.3 miles, with a residential population of 15,000. Inside the chlorine room, the vulnerability i s 0.9 miles. Since the plant is located on the edge of Lake Erie, there are no residences to the west, northwest, north and north east. During the summer, there is the possibility of a number of boaters in the circle of vulnerability, particularly in the two nearby marinas. A U.S. Coast Guard station lies 100 yards to the south of the plant. In such a major event, evacuation of the plant and adjacent areas would be the top priority. The Fire Dept., Coast Guard, and police department would all be called to assist. A mitigating condition is that the plant is locate at a somewhat lower elevation than the nearby residential areas and businesses to the south. This could slow the spread of the gas up into these areas, as the heavy chlorine gas would tend to settle in the adjacent lower lake and river areas. No permanent damage would occur to the waterways or permanent structures, but hazard to health is very real, particularly in the nearby areas. This worst-case scenario i s highly unlikely. No such event has ever occurred at either of the treatment plants. More likely is the alternate release scenario. This could occur from an improperly connected fitting or a faulty main valve. This kind of leak could be most often stopped by closing the main valve, correcting the source of the leak, then cautiously putting the tank back in service. If the valve itself is faulty, equipment is readily available in the chlorine B-Kit to seal-off such a leak, afterwhich the chlorine supplier would be contacted to come and remove the problem cylinder. This scenario is described as 200 lb. leaking over a period of 10 minutes. The vulnerability distance is 0.1 miles. There are no residences within this distance, other than up to a dozen persons at the Coast Guard station to the south. Plant personnel, boaters and fisherman in the immediate area would be the only ones affected. No leak of this size has ever occurred, but it is a remote possibility. There have been no leaks of a measurable quantity at the Black River plant during the past five years. All operators are given training and drills in using the Scott Air-Pak SCBA, and Chlorine B-Kit. Most recently, May 26, 1999, they attended a Chlorine safety seminar given by our current chlorine supplier. Chlorine supply is checked and adjusted several times each shift by operations personnel, insuring that a potential problem may be noticed long before it becomes an emergency. Chlorinators and ancillary equipment are overhauled and tested at least once per year; the chlorine detector is tested each month. Our emergency contingency plan is reviewed annually each May prior to our summer effluent disinfection period. We have just converted one of our two chlorinators over to a more modern and simpler system. The new system is smaller and less susceptible to problems than the previous 11 year-old unit. Though safe, the older units require more maintenance. We plan to chang e the remaining chlorinator next year. |