City of DuBois Sewage Treatment Plant - Executive Summary
The City of DuBois Wastewater Treatment Facility is located just outside the City limits in neighboring Sandy Township. The plant treats approximately 3 million gallons of sewage per day. The treated sewage is disinfected with chlorine prior to discharge.
The facility's approach to chemical safety includes training of facility personnel in the proper of toxic chemicals to lessen the risk of accidental releases. Another approach is to use and store the amount of a chemical needed without a large supply of the stored chemical.
Chlorine is a toxic gas and hazardous chemical. The threshhold amount for preparing a Risk Management Plan (RMP) is 2,500 pounds per one process. The treatment plant has a maximum of 6,000 pounds of chlorine at the site. However, there is only one covered process which contains a maximum of 4,000 pounds of chlorine.
The one covered process involves the storage of two 2,000 pound cylinders of chlorine. These are located outside the chlorine building on racks.
Because they are stored in close proximity to one another, they are considered only one process. The maximum amount of chlorine stored in this process is 4,000 pounds. Since it is more than the 2,500 pounds allowed, it is a covered process.
The other 2000 pounds of chlorine is located in the chloine building. It is used for the disinfection of the treated sewage. The chlorine building is equipped with the proper ventilation, alarms, and safety measures. The maximum amount of chlorine inside the building is 2,000 pounds. If another cylinder is inside the building, it is empty and awaiting removal from the building. Since the maximum amount is below 2,500 pounds, it is not considered a covered process.
Because there is one covered process, a worst-case scenario and an alternative scenario was analyzed for potential off-site impacts involving the public sector.
The worst-case scenario considers the potential hazards if the two 2,000 pound cylinders would release the entire conten
ts of chlorine in a ten minute period. The analysis also assumes that the atmospheric condition are at the most stable conditions to carry the gas the farthest. The analysis was performed utilizing the EPA's RMP*Comp computer model. Based on this analysis, the off-site impacts to the 4,000 pounds of chlorine being released in a ten minute period would range 1.9 miles from the treatment plant. The estimated population affected is approximately 13,000. The likelyhood of the worst-case scenario becoming realty is remote considering the following factors; the cylinders are mainly in storage, the method to move the cylinders is by a mechanical hoist system, and if one cylinder would rupture due to falling from the hoist, the second cylinder most likely would not be affected.
The alternative release analysis is a more realistic assumption of a release that could occur. The most likely release would be the rupture of one tank by some outside force. This analysis assumes that 2,000 pou
nds of chlorine are released in a thirteen minute period. Also, it assumes that the atmosphere is not as stable and the gas would dissipate at a faster rate. By utilizing the EPA's RMP*Comp computer model, it is estimated that the off-site impacts would range 0.3 miles from the treatment plant. A release of this type is estimated to affect a population of approximately 180.
To avoid accidents from occurring, the personnel are trained in the proper procedure for moving the cylinders. The method for moving the cylinders is an automatic hoist system. Several safety procedures are performed during the moving process. First, this operation is not performed alone. Second, when the hooks are attached to the cylinders, they are inspected to assure a secure connection. Third, before the cylinders are lifted the chains are inspected for loose links that could fail. Lastly, the hoist is raised and moved slowly to prevent any jerking of the cylinder. Also, the personnel are trained in c
hlorine leak repair to minimize the affects of a leak.
Due to the safety procedures already incorporated at the plant, there have been no accidental releases within the last five years.
The facility has an emergency response program in place. If a leak were to be detected, the facility coordinator will initiate an emergency response by notifying the local Emergency Communications Center. The center will then notify all of the emergency responders. If required, a public notification and evacuation plan would be initiated. This would affect some local schools and hospitals. Plans are in place for the evacuation of these and similar facilities.
There are no major changes to take place to improve safety at the plant. The only minor change noted is that the training or refresher training is being planned to take place annually rather than every 2-3 years.