Medina County Liverpool (SD #500) WWTF - Executive Summary
Executive Summary |
The Liverpool wastewater treatment plant is a ten million gallon per day facility that removes pollutants from municipal sewage prior to discharging the clean water to the West Branch of the Rocky River. As a last step in the treatment of the wastewater, chlorine is added to kill any remaining bacteria. The chlorine used in this process is purchased in one ton cylinders. Typically five (5) cylinders are stored in a chlorination building specifically designed for this purpose. Two (2) of the cylinders are in use and connected to the chlorination system while three (3) are waiting to be used. Full containers are tagged as such with a red tag while empty cylinders are similarly tagged with a green tag.
Chlorine Accidental Release and Emergency Response Policies
The administration at the Liverpool treatment plant, in conjunction with plant operators, have developed suggested operating procedures (SOPs) for the handling of the chlorination facilities.
These procedures outline in detail how cylinders are connected to the chlorine feed system, the number of personnel (including observers) to be involved in the changing of the cylinders, the frequency at which chlorine piping and valves are to be replaced, etc.. All operators are trained to know the SOPs and this training is reviewed periodically during routine safety meetings.
All cylinders are contained in a concrete block building with a precast concrete roof to minimize any possibility of fire in the building. The cylinders are stored on appropriate concrete saddles on a concrete floor. No other materials are stored in the building. A chlorine leak detection and alarm system is in place to alert personnel of any chlorine leaks.
The Liverpool Treatment Plant administration, along with the County Sanitary Engineers Safety Coordinator and County Local Emergency Planning Commission (LEPC), have developed a spill response document known as the Chlorine Spill Investigative/Respo
nse Procedure. This document provides step by step instructions regarding steps to be taken when responding to a chlorine leak.
Worst Case/Alternate Release Scenario
As part of this plan, a worst case and a more likely alternative release scenario are to be researched. The worst case release scenario calls for the release of the entire content of one cylinder in four minutes. As the cylinders are constructed of one inch thick steel with recessed fill/discharge valves, the possibility of the loss of the entire content of one tank within this time period is remote. However, The rules governing the writing of the risk management plan require the worst case scenario to anticipate the instantaneous release of the largest vessel on site. The loss of one full cylinder in four minutes is considered to have fulfilled that requirement.
The alternative release is considered to be a more likely scenario of how a release would occur. In this scenario we have considered that a pipe has bro
ken or a valve has failed leaving a one half inch hole from which the chlorine can escape. The plant alarm has sounded but it has taken fourteen minutes for an operator or the fire department to don their SCBA, enter the building and secure the leak.
Modeling for the worst and alternative release scenarios was conducted using the LEPCs Areal Locations of Hazardous Atmospheres (ALOHA) software. Both of the scenarios assumed a wind speed of 5 mph and the loss of the entire contents of a full tank. The ALOHA program indicated that the zone of influence for the worst case and alternative case scenario existed within a 3.2 and 2.6 mile radius, respectively, of the treatment plant.
Five Year Accident History
There has only been one incident regarding a chlorine release during the past five years at the plant. The leak occurred as an operator opened a valve prior to completing the connection of a fresh chlorine cylinder to the system piping. The valve was quickly closed and the rele
ase contained within the building. The leak did result in irritation to the operators eyes.
Emergency Response Program and Planned Improvements
As indicated previously, Medina County has labored together with the LEPC to develop a release response program. Written proceedures are readily available to plant operators that includes steps to be taken during a release, entities to be contacted and the telephone numbers for those entities. Personnel at the plant are given training regarding the response procedures and refreshers are completed periodically during plant safety meetings.
This spring the local fire department was invited to tour the entire treatment plant. Special attention was given to the chlorine storage building, the location of the SCBAs and other emergency equipment. In addition, the County has discussed conducting drills with the LEPC and local fire department to practice responding to chlorine releases. These efforts along with safety operating procedures alr
eady in place will minimize the possibility of leaks and minimize response times in the event a leak does occur. This will result in a safe working environment and the protection of the local community.