Skagit PUD #1 Water Treatment Plant - Executive Summary
The Skagit PUD #1 Water Treatment Plant (Skagit WTP) treats and supplies water to the surrounding Skagit Valley. During treatment, chlorine is used as a disinfectant. Chlorine is the only chemical at Skagit WTP regulated by the Risk Management Program (RMP). The chlorine supply system is closely monitored and controlled to prevent accidental releases to the environment. It is Skagit WTP's policy to manage the chlorine process "using the highest standards for the protection of our people, our customers, the community, and the environment in order to ensure a safe and effective facility."
The Skagit WTP uses chlorine as a disinfectant for the public water supply. One ton chlorine containers are brought to the plant and connected to a manifold supply. Chlorine gas is supplied under vacuum to the water supply. The amount of chlorine in the supply water is carefully controlled using computerized controllers, monitors and continuously supervised by certifi
Accidental Release Prevention and Emergency Response
The toxicity of chlorine at high concentrations make it necessary for the Skagit WTP to observe certain safety precautions to prevent unnecessary human exposure, and reduce the threat to the personal health of our employees as well as nearby members of the community. It is WTP policy to adhere to all applicable federal and state rules and regulations. Safety depends upon the manner in which we handle toxic chemicals including equipment design and safe handling procedures used to operate the equipment. WTP's release prevention program is based on four principles; inherently safe design, effective written procedures, training, and the goal of continuous improvement. The chlorine storage and handling equipment meets or exceeds design codes and standards as well as incorporating good engineering practices recommended by The Chlorine Institute. Written operating and maintenance procedures are prepared and reviewed annu
ally for accuracy and safety. Operating and maintenance personnel are thoroughly trained on proper procedures and safety hazards, and are provided with regular refresher training.
The WTP has developed a comprehensive Emergency Response Program. In the event of an accidental release , the emergency response plan includes notifying the Local Emergency Planning Commission (LEPC), the Washington State Emergency Management Division, and the National Response Center. Plant personnel receive classroom training on implementation of the response plan in addition to participating in training exercises.
Worst and Alternative-Case Release Scenarios
The worst-case release scenario from the Skagit WTP involves a catastrophic failure and release of the entire contents of a 1-ton liquid chlorine container. Using EPA's dispersion modeling program, RMP*Comp, the maximum distance downwind from the chlorination process to an endpoint concentration of 3 ppm chlorine is 0.9 miles. The worst-case imp
act distance is calculated using EPA mandated assumptions which are conservative. The worst-case analyses assumes that the release will occur during very stable climatic conditions not normally observed.
The alternative release scenario was developed during a detailed Process Hazard Analyses involving operating, and maintenance personnel. The alternative release scenario is intended to represent the largest release that could reasonably be expected to occur. The alternative release selected was the a damaged vacuum regulator valve on the chlorine gas supply line. The amount of chlorine released was estimated at 2000 pounds based on dropping a 2000 pound container, splitting the seam, and releasing the entire contents over a period of 13.3 minutes. Using EPA's RMP*Comp model, it is calculated that this release could exceed 3 ppm chlorine up to 0.2 miles downwind.
Five-Year Accident History
During the five year period between May 1994 and June 1999, the Skagit WTP has had no doc
umented reportable release of chlorine