City of Edmonds Wastewater Treatment Plant - Executive Summary
The Edmonds Wastewater Treatment Plant approaches chemical management in the safest manner possible to protect the public and the environment. |
Like 98% of US water and wastewater treatment plants, we utilize chlorine to disinfect our treated water. At the Edmonds Wastewater Treatment Plant, we use approximately 200 pounds of chlorine each day as part of the disinfection process that provides our community with effective sanitation. Chlorine has been safely used to disinfect drinking water for nearly 100 years, reducing or eliminating the risk of such waterborne diseases as cholera, typhoid, and dysentery.
We have long understood the hazards of handling chlorine, which if not done properly, can pose a risk to the community. Chlorine is listed in the EPA's new Risk Management Program Rule (RMPR). Since we have more than 2,500 pounds of chlorine on our site, we are required by the EPA to submit a Risk Management Plan. The RMPR has ensured that in the unlikely event of a release, lo
cal area emergency responders and other authorities are fully trained and ready to engage specific plans to remediate the situation quickly.
The Edmonds Wastewater Treatment Plant has used chlorine to disinfect water for more than 20 years. Since the plant was upgraded in 1991, we have not had any accidents or leaks that resulted in chlorine being released to the environment. The threat to the environment is an air emissions issue, since a chlorine leak would occur in a gaseous state. A chlorine leak, therefore, would not send waters with high chlorine levels into Puget Sound. Chlorine is supplied in cylinders delivered to the plant by a vendor, and is stored in a room specially designed to contain chlorine gas leaks. A chlorine leak in this room would be routed to a scrubber that would remove the chlorine gas. To protect the public, the chlorine cylinders in the storage room are chained down to prevent any movement in the event of an earthquake. In addition to the cylinder cons
traints, a specially designed room, and the dedicated air handling system, the room also has continuous air monitoring. These sensors will alarm the plant's computer system as well as activate an audible plant siren if even a small amount of chlorine is detected.
The new EPA regulation requires the City to perform two analyses: a worst case release scenario, and an alternative release scenario. The EPA dictates the conditions in the worst case scenario, which assumes that the largest storage tank fails catastrophically to empty itself in 10 minutes on a day with very low wind. Although this release may be physically impossible, EPA mandates its consideration. In reality, the chlorine would be released from the storage cylinder as a flashing liquid that would probably auto-chill and form a puddle of "chlorine ice," only a fraction of which would evaporate in 10 minutes. In the required worst case release scenario, the storage room would be unable to contain the gas and chlorine gas
would be released to the atmosphere. Using EPA's model, chlorine would be detectable over an area with a radius of 0.9 miles from the Treatment Plant.
In light of the fact that the worst case release scenario is not likely to occur, EPA also mandates that each facility create an alternative release scenario that is more realistic than the worst case scenario. The City hired an outside engineering company to analyze the plant, its chlorine handling equipment and process, and interview plant employees to determine the most likely alternative release scenario. A systematic evaluation of the overall process was conducted and the firm determined that a broken connection pipe would be the most likely mode of failure. The amount of chlorine to leak from the pipe in such a scenario is within the operating parameters of the existing scrubber. Such an incident would be detected by the sensors, contained within the room, and vented to the scrubber until the tank valve is closed. Assuming
that some of the gas was able to leak out of the room, the engineering company estimated that chlorine would be detectable approximately 150 feet from the storage room.
In addition to equipment and building safeguards, safe handling of chlorine is also addressed through a prevention program. This program is covered under a separate regulation called Process Safety Management, and has been in place for years. Issues such as training, hazard review, operating procedures, maintenance, and safety information are all included in the Plant's prevention program.
The response plan for a chlorine leak varies depending upon the severity of the leak. Trained plant personnel deal with small leaks that are contained. Response to a large leak or an unconfined leak would be directed by the Fire Department. A dedicated team in the Lynnwood Fire Department has been specially trained to work with hazardous chemical releases, and would respond to any leak that could threaten the public. Additional
ly, the plant worked closely with the local emergency planning committee (ESCA) in developing a separate hazardous materials response plan. This interaction between our facility and emergency responders provides information to be exchanged and procedures developed that will assure a timely and appropriate response.
We are confident that the added protection of the new Risk Management Plan will ensure that our personnel, the environment and the community continue to remain safe and healthy.