O. N. Stevens Water Treatment Plant - Executive Summary
The O. N. Stevens Water Treatment Plant (the Plant) provides drinking water for Corpus Christi, Texas, and for surrounding communities. The Plant is located at 13101 UpRiver Road, in the northwestern part of Corpus Christi, Nueces County, Texas. The Plant provides approximately 60 million gallons of drinking water per day, during the winter months, and 110 million gallons per day, in summer. The City of Corpus Christi has a commitment to safely providing drinking water to this region. |
Chlorine is the only regulated chemical used in the water treatment process. Chlorine is used as an ingredient to kill the pathogens in the water and to make the water safe to drink. Because of the enormous amount of water that has to be treated, a large quantity of chlorine must be kept at the site for use. There are other chemicals that are used in the treatment of the water, but the other chemicals are stored and used in smaller quantities, making them exempt from the Risk Management Plan regul
ations. Safety is of utmost importance, when working with and around any of the chemicals in the Plant.
The O. N. Stevens Water Treatment Plant has been using chlorine for more than 40 years, and there are no reportable incidents of chlorine releases. The excellent track record is founded in the methods used to deliver the chlorine into the water.
During the process, chlorine is normally stored under pressure as a liquid in two 90-ton rail tank cars. Even though the 90-ton storage containers are designed to travel on rails and designed to take impacts at high rates of speed, at the Plant, these containers are stationary and are anchored in place during the delivery of chlorine to the process. Liquid chlorine rail tank cars are near the evaporators, reducing the length of pipe required for the liquid chlorine to travel. Reduction in the length of pipe containing liquid chlorine, reduces the hazard, because liquid chlorine has a higher risk potential than chlorine gas. From the e
vaporators, the chlorine gas is transported to the chlorine injection points under a vacuum system, which further reduces the chances of chlorine escaping into the atmosphere.
As a backup for chlorine, one-ton cylinders are used on a temporary basis. These cylinders are normally not kept at the plant. If problems should arise in the normal chlorination process, the one-ton cylinders will be ordered, delivered, and used.
All of the projects that are performed at the Plant are implemented with safety at the forefront. Competent and knowledgeable engineers design the plans, and the materials of construction are chosen to provide mechanical integrity. Rail tank cars are equipped with excess flow valves, which will shut off the flow of chlorine should a pipe in the system sever completely, and the system is designed with proper safety relief valves as needed. Area gas monitors are used to detect any leaks, and video cameras are used for remote early detection.
During the design ph
ase, special consideration is given to safety by reviewing chlorine process changes. A team has been created to perform a Hazard Review of all projects that involve significant changes. This team is composed of employees who are experts in different areas of the plant functions, thus evaluating all of the aspects of safety that may be affected. The hazard review can be very detailed and intricate, if new systems are being introduced or major changes are occurring; or they can be more relaxed, if minor changes are being made. In either case, the Water Production Superintendent will evaluate all of the projects for hazard review requirements before they are bid for construction. Reviewing every change that occurs in the chlorine system increases the level of safety for the community.
Some of the technological equipment that is in place includes a Supervisory Control Data Acquisition (SCADA) system, an operator actuated audible alarm system, and a video monitoring system. The SCAD
A system is a computerized system that administratively controls the chlorine process and controls equipment that is used to treat and distribute water throughout the community. Many of the chlorine system's alarms can be connected to the SCADA, and early detection can be acquired. Hooking up to the SCADA allows the operations personnel to give an early warning and to take steps to stop a release within a reasonable time after a release occurs. Time is of essence in an emergency, and this system provides the capability of detecting problems early. Operator actuated alarm allows early warning to Plant personnel of any emergency, should it occur. The video monitoring system acts both as a security measure and as a measure for early detection and location. Remote monitoring of the chlorine system allows operations personnel to detect the presence of unauthorized personnel at the facility and the location of a release, should it occur.
A water spray mitigation system has been install
ed. This system has the capability of creating a water curtain on either side of the tank car and diverting the runoff to an underground holding tank. This is an active system, requiring human intervention. The holding tank is designed to contain the chlorine liquid near the rail car, should a release occur. The tank is big enough, so that the operators will have the time needed to stop the release without the tank spilling over. Design allows for chlorine to be captured and neutralized as required, after the incident is over.
A Security Guard is posted at the entrance to the facility. The purpose of the guard is to keep unauthorized personnel out of the Plant and to document whom is in the Plant during an emergency, should one occur.
Training is an important part of chlorine safety. Newly hired employees are required to complete chlorine safety training before they are allowed to work on any of the components of the chlorine system. The training program includes on-the-job
training, as well as in-class training. Refresher training is an integral part of the program, along with hands on application exercises. Qualified personnel are used to train the employees in all areas of their job, which impact the chlorine process.
All of the Plant personnel are trained in the performance of their duties. Operations personnel are trained to operate the chlorine process in a safe manner. Operations personnel are required to be licensed by the Texas Natural Resource Conservation Commission (TNRCC), and they are required to follow internal operating procedures regarding operations of the chlorine system. Maintenance personnel are trained to work on materials and equipment according to manufacturer's recommendations and according to Chlorine Institute guidelines. Preventative maintenance on all equipment and materials is also performed in a timely manner, in accordance with manufacturer's recommendations.
As part of the Risk Management Plan, every fixed facility
that manages a regulated substance must develop an "Alternative Release Scenario" (ARS) and a "Worst Cast Scenario" (WCS). Similar to the WCS, the ARS is an unlikely scenario, but the ARS is not impossible. In order to maximize the impact of the ARS, a maximum condition was chosen. The condition assumed that a pressurized liquid chlorine line would be breached, and a release of liquid chlorine would occur with the release rate just below that of the excess-flow-valve-seating rate in the chlorine rail tank car. The breach could be caused by either deterioration or some form of accident. Using the EPA's Risk Management Program Guidance (40 CFR part 68) for POTW's, "Section 126.96.36.199. Chlorine, Flashing Liquid Releases," the resulting figure would be 0.75 miles. What this means is that if an inadvertent spill should occur and should release the maximum amount of liquid chlorine possible, the area of concern would be an area down wind of up to 0.75 miles.
The specifications for the WC
S are very rigid and require that an assumption be made such that the entire contents of the material are released immediately. It also requires the entire contents to flash (or evaporate) into a gas in a period of 10 minutes. This scenario is highly unlikely, but every stationary facility with a regulated toxic substance must perform this exercise. There is a maximum of three 90-ton railcars of chlorine at this facility at one time. Using EPA's Offsite Consequence Analysis, RMP*Comp, the resulting area of concern is a radius which is "greater than 25 miles" down wind from the O. N. Stevens Water Treatment Plant (O.N.S.).
Auditing our safety methods and procedures is a very important part of our safety program at the Plant. During the course of the workday, each employee is watchful for possible improvements, and there is an avenue for employee suggestions to be implemented. Inspections of the materials and equipment are conducted twice a year, or sooner if the preventive mainte
nance requires more frequent inspections. Every three years, an independent consultant performs a complete safety inspection of the chlorine system, to determine any safety improvements that can be made to the system.
All serious incidents shall be thoroughly investigated. The effort of the investigations will be concentrated to knowing the real factors of the incident and to taking steps to improve conditions, so that those incidents will not happen again. An Incident Investigation Team will decide on the necessary improvements to the system, to eliminate or reduce the revealed hazards.
An emergency response plan has been developed that will include joint participation of employees at the Plant, Corpus Christi Fire Department Haz-Mat units, our Emergency Management Department, and the City of Corpus Christi/Nueces County Local Emergency Planning Committee (LEPC). Exercises with the Fire Department are being planned, in order to familiarize the Fire Department with specific equip
ment functions and their locations at the Plant and to familiarize employees with emergency response procedures and corresponding actions.
In addition to training our employees, the community is also involved in learning their respective response roles, should a release occur. The Northwest Community Advisory Council is a group of concerned citizens that meets once a month with industry representatives, to share citizen's concerns and to develop plans of action to distribute information to the community about responding to emergencies. The LEPC helps to disseminate information to children in schools and the community by having "Health and Safety Fairs" in the surrounding area.
As we continue to improve our overall safety at the Plant, we will be developing closer ties with our community by: (1) planning exercises in conjunction with our LEPC, our Department of Emergency Management, our Fire Department, and local refineries, (2) increasing our efforts to assist the LEPC in communit
y awareness, including the placement of alert radios in all of the schools in the area, (3) increasing the level of training and skill of our personnel, and (4) continuing efforts of community awareness in responding to emergencies. From safety at the Plant to joint efforts with the community in response to emergencies, efforts will continue to be made to keep the safety of our employees and the community as a top priority.