Motts Run Water Treatment Plant - Executive Summary
The Motts Run Water Treatment Plant (WTP) located at 5700 River Road, Fredericksburg, VA 22407 is owned by Spotsylvania County and operated by Spotsylvania County Department of Utilities (SCDU). The facility is a new, state-of-the-art WTP scheduled to become operational in January 2000. The Motts Run WTP processes water received from the Rappahanock River and distributes it to the surrounding population. The facility is designed to treat up to 12 million gallons per day (MGD) of water. |
As part of the treatment process, the Motts Run WTP uses chlorine to disinfect, or destroy the waterborne disease causing organisms present in the source water, oxidize iron, manganese, color and organic matters, reduce taste and odors in the finished water and provide a protective disinfecting residual in the finished water to inhibit growth of organisms in the distribution system and protect against other potential microbial contamination.
Chlorine is delivered to the Motts Run WTP in one-ton (2,0
00 pound) gas containers. The facility can store up to twelve containers at one time. The maximum amount of chlorine stored at the facility at any one time is 24,000 pounds.
Chlorine gas is a toxic substance that is regulated by the U.S. Environmental Protection Agency (EPA). Because Motts Run WTP stores more than 2,500 pounds of chlorine at the site, it is subject to the EPA's Risk Management Program Rule codified in 40 CFR 68. The Motts Run WTP has prepared a Risk Management Plan (RMP) in accordance with the requirements of 40 CFR Part 68. In addition, Motts Run is subject to the OSHA Process Safety Management (PSM) requirements. A program level three PSM Plan was prepared for Motts Run WTP to meet the requirements of both EPA and OSHA. The PSM Plan is included in the RMP as an appendix.
The Motts Run WTP has been designed with extensive safety features to prevent the accidental release of chlorine. The facility is equipped with a hoist system to unload
the one-ton containers from the delivery trucks directly into the Chlorine Storage Room. The hoist system is also used to load the chlorine containers onto the scales in the Chlorine Storage Room. Before accepting any chlorine container and while the container is still on the truck, facility operators check the condition of the container and inspect it for leaks.
There are three separate, fully enclosed rooms at the Motts Run WTP used for the chlorine system; the Chlorine Storage Room, the Chlorine Feed Room, and the Chlorine Scrubber Room. The three rooms are adjacent to each other and each of the three rooms is equipped with a chlorine detector/alarm. If chlorine is detected in any of these three rooms above 1 ppm, an alarm is sounded. The Chlorine Storage Room also has an emergency ventilation system that can draw the ambient air from the room through a Chlorine Scrubber system. If chlorine is detected above 1 ppm in the Chlorine Storage Room, the normal exhaust system is s
hut down and the Chlorine Scrubber system is automatically activated. In addition, this system can be manually activated using the Emergency Pushbutton Panel located outside the entrance to the Chlorine Storage Room. Appendix A includes the equipment specifications for all of the equipment associated with the Chlorine Feed System at the facility.
Motts Run WTP personnel who work with or near the chlorine system receive extensive training to prevent the accidental release of chlorine. Employees receive initial training before working at the facility as well as continued training whenever there is a change in equipment or operating procedures. Annual emergency response training is also to be conducted at the Motts Run WTP.
As part of the RMP, the EPA requires that facilities subject to the requirements of 40 CFR 68 conduct an offsite consequence analysis to provide information to the government and the public about the potential consequences of an accidental c
hemical release. The off-site consequence analysis consists of two elements:
v a "worst-case" scenario
v alternative release scenario
For each of these two scenarios, facilities are required to estimate the distance that a chemical plume will travel before its concentration falls below the EPA established "toxic endpoint". Facilities are also required to estimate the population and other environmental receptors that may be impacted under each release scenario.
The worst-case release scenario is an unlikely event, used solely for planning purposes. EPA has defined the worst-case scenario as the release of the largest quantity of a regulated substance from a single vessel that results in the greatest distance to an endpoint. In broad terms, the distance to the endpoint is the distance a toxic vapor cloud will travel before dissipating to the point that serious injuries from short-term exposures will no longer occur. The release is directionally independent, therefore, the distance
to the toxic endpoint is assumed to include the entire radius of a circle drawn around the facility. The EPA model RMP*Comp was used to estimate the worst-case release scenario of chlorine gas. The worst-case scenario assumed the complete loss of the contents of a one-ton chlorine gas container (2,000 lbs) in a 10-minute period. The model for the worst-case scenario was run assuming the release occurred outside the building, and that the area immediately around the site has many obstacles (trees). Based on the RMP*Comp model, the worst-case scenario endpoint distance for the Motts Run WTP is a distance of 1.3 miles.
The EPA also requires facilities to model an alternative release scenario or "more-likely" release scenario, which also impacts offsite receptors. Because the Motts Run WTP is new, there is no historical data of a chlorine release at the facility. Therefore, to model an alternative release scenario, it was decided to use the release of chlorine from a tubing failure
, bad connection or valve failure resulting in a 5/16-inch diameter valve body opening. The average release rate used for the model was 10.5 lbs/minute for a duration of 60 minutes. (The release rate selected was taken from the AWWA Guidance, "Compliance Guidance and Model Risk Management Program for WTPs"). Using the EPA model RMP*Comp, the alternative release scenario endpoint distance was then calculated. The alternate release scenario also took into account the passive mitigation provided by the storage of the chlorine in enclosed rooms. Based on the RMP*Comp model, the alternative release scenario endpoint distance for the Motts Run WTP was calculated as 0.1 mile (528 feet). It is approximately 260 feet from the Chlorine Storage Room to the property boundary of the Motts Run WTP.
Five-Year Accident History
The Motts Run WTP is a new state-of-the-art facility scheduled to become operational January 2000. There have been no chlorine gas releases from the Motts Run WTP.
The SCDU has prepared an Emergency Response Plan for the Motts Run WTP that addresses both low risk and high risk releases of chlorine gas. The facility operators are trained to respond to a low risk release of chlorine within the chlorine process area. The operators, wearing the proper personal protective equipment, are capable of entering the storage area and repairing or replacing faulty equipment. In addition, the Motts Run WTP is equipped with a Chlorine Scrubber System to neutralize any chlorine gas released in the Chlorine Storage Room.
In the event of a major release (High Risk), SCDU has an arrangement with the local Spotsylvania County Fire and Rescue to respond to emergencies. If the Spotsylvania County Fire and Rescue determines they cannot handle the emergency, they will contact the City of Fredericksburg Fire Department for assistance. The Fredericksburg Fire Department is the Regional Hazardous Materials Team under contract with the Virginia
Department of Emergency Services (VDES). If there is a major release, authority for the response actions shifts to the offsite responders. The offsite responders will instruct the Motts Run WTP personnel and inform the public/media of evacuation and/or sheltering in place as necessary.
First aid procedures are also provided in the Emergency Response Plan.
Planned Changes to Improve Safety
The Motts Run WTP does not currently have any planned changes to improve safety. However, SDCU will continually review the existing operating procedures, process safety information and training program to protect the safety of its employees and the surrounding population.