Williston Water Treatment Plant - Executive Summary
EXECUTIVE SUMMARY |
The Williston Water Treatment Plant is located approximately four miles southwest of the City beside US Highway #85 on the north bank of the Missouri River. The plant is built on a side hill with the Burlington Northern Santa Fe Railroad tracks below the plant and rural residential subdivisions to the north and west of the plant on higher ground. Across the river to the south is US Government property manged by the US Army Corps of Engineers and leased to the North Dakota State Game & Fish Department as a wildlife management area. A boat ramp is located directly across the river from the plant.
The purpose of the plant is to treat water taken from the Missouri River for the potable water supply for the City of Williston and some of the surrounding area. Primary processes within plant include lime softening and filtration with chlorine used as a disinfectant.
The chlorine room is located on the lower level of the plant with separate access from the exterior onl
y. Chlorine is delivered in one ton cylinders to a loading dock at the chlorine room. A maximum of three one ton cylinders are kept on hand at any given time. One cylinder is connected to the chlorinator in use, one cylinder is connected for automatic changeover and the third cylinder is either full or waiting to go on line or empty and waiting to be replaced.
Chlorinators are vacuum operated so all chlorine distribution lines in the plant outside of the chlorine room are low-pressure vacuum lines. If the vacuum is broken on any of these lines the chlorinators automatically shut down. The chlorine room is equipped with a high volume exhaust fan that starts when the room light is turned on; an observation window in the lower portion of the door to check the room before entering and a chlorine detector located outside of the room on the exhaust and connected to an alarm system. Each tank is equipped with a position shut off valve and an emergency relief valve.
In practice, the ch
lorinator is connected to the tank prior to opening the control valve. The control valve is closed prior to disconnecting the chlorinator. Only a minimal amount of chlorine is able to escape during the disconnection operation.
All four full time employees at the plant are certified water treatment operators at various levels have been trained in the formal classes conducted by the ND State Department of Health and Environmental Sciences and have had on the job training from senior operators. Each has been trained in operating the chlorination system and the safety devices on the system.
The worst case scenario considered the venting of one entire cylinder of chlorine gas within the chlorine room in 10 minutes. With the prevailing winds from the northwest and the density of chlorine, the probability is the gas would migrate down to the river surface and away from the human population. However, in the event of southerly winds the gas might be driven up the hill to the residential
areas. Based on Urban Topography the toxic end point is calculated to be 0.9 miles in any direction from the storage area.
The alternate release considered also looked at the complete release of one full container through a 5/16" valve throat at an increased wind velocity of three meters/second. In this scenario, the end point distance was only 0.09 miles, which exposes remains on the plant site. Both scenarios were formulated using EPA's RMP Off-Site Consequences Analysis Guidance Manual. Again, the release was considered to be within the chlorine room.
In the event of an incident plant personnel would evacuate the plant and notify emergency personnel. Williams County Emergency Services, Rural Fire Department and Williams County Sheriff's Office would be the primary services called upon with the Sheriff's Office getting the initial call. The Sheriff's Office maintains a call list of the various areas in the County for evacuation notices. Evacuation would be the responsibilit
y of the Sheriff's Office while the responsibility for dealing with the problem on site would fall to the Rural Fire Department. Williams County Emergency Services would provide coordination, logistics and special services. Additional manpower is also available from the Municipal Fire Department, Police Department, Ambulance Service, Public Works Department and Plant Staff. Emergency personnel in Williams County periodically conduct joint training exercises covering various emergency scenarios.
There have been no accidental releases of chlorine gas for the plant in its 40-year history.