City of Marysville Wastewater Treatment Plant - Executive Summary

| Accident History | Chemicals | Emergency Response | Registration | Source | Executive Summary |

Executive Summary 
Marysville Wastewater Treatment Plant (MWWTP) receives wastewater from the City of Marysville and processes and disinfects the water before releasing it to Steamboat Slough outfall.  The MWWTP is located at 2 Columbia Avenue in Marysville, Washington.  The wastewater is disinfected by introducing chlorine to the wastewater to kill harmful bacteria. 
CI2 is the only toxic chemicals regulated by the Risk Management Program (RMP) that is present at the MWWTP.  The chlorine system is closely monitored and controlled to prevent accidental releases to the environment.  It is MWWTP's policy to manage the chlorine process "using the highest standards for the protection of our people, the community, and the environment in order to ensure a safe, productive and efficient facility". 
Regulated Chemicals 
MWWTP uses chlorine as a disinfectant to eliminate harmful bacteria in the wastewater before discharge.  Chlorine, a gas at ambient temperatures and pressure, is delive 
red to MWWTP in 1-ton containers and unloaded into an enclosed process building. 
In the unlikely event of an accidental release, Chlorine would either be released directly into the air as a gas or evaporate into the air from liquid pools formed in low spots on the floor.  The primary health affect of Chlorine gas is respiratory irritation.  In sufficient concentrations, the gas irritates mucous membranes, the respiratory tract and the eyes.  Following a release, Chlorine gas will migrate downwind and disperse to below health effect concentrations. 
Accidental Release Prevention and Emergency Response 
The toxicity of Chlorine at high concentrations make it necessary for MWWTP to observe certain safety precautions to prevent unnecessary human exposure, and reduce the threat to the personal health of employees as well as nearby members of the community.  It is MWWTP's 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.  MWWTP's release prevention program is based on four principles; inherently safe design, effective written procedures, training, and the goal of continuous support.  The chlorine storage and handling equipment meets or exceeds design codes and standards as well as incorporating good engineering practices recommended by industry groups, such as The Chlorine Institute.  As a result, MWWTP's equipment incorporates inherently safe designs.  Written operating procedures are prepared and reviewed annually for accuracy and safety.  Operating and maintenance personnel are thoroughly trained on proper procedures and safety hazards, and are provided with regular refresher training.  Equipment and procedures are frequently evaluated and updated with the goal of continuous improvement in both operation and safety. 
MWWTP's emergency response program integrates OSHA's and EPA's preparedness 
planning response and training requirements.  In the event of an accidental release, the emergency response plan includes notifying 911 dispatch, which will notify local responders.  Plant personnel receive classroom training on implementation of the response plan in addition to participating in training exercises.  The Fire District Hazardous Response Team would actually repair or evacuate the area in the event of a genuine release, because we haven't had HAZWOPER training.  
Worst-case and Alternative Release Scenarios 
The worst-case release scenario at MWWTP involves the catastrophic failure and release if the entire contents of a 1-ton liquid Chlorine ton container. Using EPA's dispersion modeling program, RMP*Comp tm, the maximum distance downwind from the storage tank to an endpoint concentration of 3 ppm Chlorine is 2.2 miles.  This worst-case impact distance is calculated using EPA mandated assumptions, which are conservative.  For example, EPA requires the assumption that al 
l of the liquid Chlorine is released as a gas within 10 minutes.  Actually, only about a third of the liquid Chlorine will flash off as gas while the remaining two thirds either remains in the tank or spills on the ground and evaporates over a much longer time period.  The worse-case analysis also requires the unrealistic assumption that the wind blows constantly at a high speed in the same direction for several hours in order for the Chlorine to migrate a long distance downwind.  MWWTP believes that these calculated worst-case distances overstate the distances that harmful impacts could occur.  The alternative release scenarios are considered by EPA to be more representative of actual impacts attributable to an accidental release. 
An alternative release scenario was also developed for Chlorine.  The alternative release scenario was developed during detailed Process Hazard Analyses involving operating, maintenance, and engineering personnel, and outside experts.  The alternative relea 
se scenario is intended to represent the largest release that could reasonably be expected to occur.  For Chlorine, the alternative is based on a liquid Chlorine ton container being dropped during unloading, resulting in a 1/4 inch puncture through which the entire contents of the ton container is released.  Using EPA's RMP*Comp tm model, it is calculated that this release could exceed 3ppm Chlorine up to 0.4 miles downwind. 
Five Year Accident History 
During the five-year period between May 1994 and June 1999, the MWWTP has not had a reportable release of Chlorine.
Click to return to beginning