Elm Fork Water Treatment Plant - Executive Summary |
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INTRODUCTION The Accidental Release Prevention Risk Management Program rule (40 CFR Part 68) is similar to the Occupational Safety and Health Administration's Process Safety Management Program, which is designed to protect workers from accidental releases of hazardous substances. The Risk Management Program rule addresses over 100 chemical substances-77 of which are acutely toxic and 63 of which are flammable gases-and the accidental release of these substances. The United States Environmental Protection Agency (USEPA) estimates that over 100,000 sources are covered by the rule, including chemical manufacturers and wholesalers, certain retailers, potable water treatment systems, wastewater treatment plants, ammonia refrigeration systems, and federal facilities. The Elm Fork Water Treatment Plant (WTP) falls under this regulation because of the on-site storage of chlorine. The amount of chlorine stored is well above the threshold limit specified by the USEPA thereby making the facil ity subject to compliance with the regulation. The Elm Fork WTP personnel have complied with the USEPA Risk Management Program rule and have completed an Accidental Release Prevention Program (ARPP) Plan that contains the following required information: 7 Management System 7 A hazard assessment that establishes the worst-case and alternate release scenarios and their impact on the population and the environment (40 CFR Part 68 Subpart B). 7 A prevention program that includes safety information, a hazard review, operating procedures, training, maintenance, compliance audits, and incident investigations. (40 CFR Part 68 Subpart C) 7 An emergency response plan (40 CFR Part 68 Subpart E) The following subsections discuss details of the plan that has been implemented at the Elm Fork WTP. RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The Elm Fork WTP facility in Carrollton, Texas has an excellent record in preventing and minimizing releases of chlorine. This facility is impleme nting a program for on-site emergency responders. The emergency response policies at this facility ensure that there is emergency response coverage 24 hours per day, 7 days per week. There are also adequate provisions for coordination with outside agencies, such as the City of Dallas HAZMAT team, in the event of an emergency. In the event of a release, plant staff is receiving training to enable an on-site staff response prior to the arrival of the HAZMAT team. REGULATED SUBSTANCE The Elm Fork WTP uses chlorine as a disinfectant in the water treatment process. The Elm Fork WTP regularly has a storage maximum quantity of 205 tons of chlorine at its facility that is stored in two DOT certified 90-ton rail cars, and one 25-ton emergency storage tank. This is above the threshold limit (2,500 pounds) set by the USEPA. PROCESS DESCRIPTION The Elm Fork WTP receives raw water from the Elm Fork of the Trinity River into the treatment plant located at 1440 Whitlock Lane, Carrollton, Texas. Water is treated at the plant and subsequently pumped to the distribution network of pipelines, pump stations, and storage tanks. The existing chlorine feed facility at the Elm Fork WTP consists of (1) inside storage tanks (two 90-ton rail cars and one 30-ton emergency tank), (2) liquid feed piping and miscellaneous valves, (3) three evaporators, (4) gas piping and miscellaneous valves, (5) three chlorinators, and (6) one scrubber system. On treatment plant grounds, the two areas in which chlorine has a potential to generate a gaseous release are the chlorine storage area (items 1 and 2 above) and the chlorine process areas (items 3 through 6 above). Chlorine is mostly delivered to the Elm Fork WTP by railroad on rail spurs and stored in two 90-ton railroad tank cars, located at the Chlorine and Ammonia Building. The emergency tank is filled through a chlorine tanker truck when necessary. Chlorine is removed as a liquid under pressure of the rail car or the emergency t ank. Chlorine is withdrawn from one tank car at a time through a flexible metal connection. As the supply in one rail car empties, the supply is manually switched to the full tank car. The emergency tank is used only when there is no chlorine in either of the rail cars, which is a rare occurrence. The liquid chlorine under pressure flows through a flexible reinforced hose and hard-piped to three chlorine evaporators located in the chlorine evaporator room. The chlorine gas generated by the evaporator is then transferred to the chlorinators and is fed either to a vault leading to the rapid mix basins (pre chlorination), or the filter outlet (post chlorination). WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS The chlorine storage and process areas have associated hazards that can potentially affect on-site employees and the off-site population and environment. The U.S. EPA requires that one worst-case scenario and one alternate release scenario is reported for each regulated chemic al. Worst-Case Scenario The largest potential release of chlorine would occur through an angle valve failure on the 90-ton rail car located on the north side of the plant. This valve failure could potentially release all 90 tons of the chlorine as a gas. Under Section 68.25(c)(1), the release time for a chemical such as chlorine is 10 minutes. Passive mitigation controls were applicable to the worst-case release at this plant. The EPA-approved modeling program DEGADIS+ was used to characterize the effects of the worst case scenario at the Elm Fork facility. The distance to the toxic endpoint of 3 ppm was determined to be 5.69 miles. The estimated affected residential population is 140,000 people. Commercial / industrial areas and residential areas would be affected in the worst-case release scenario. Alternate Scenario One alternate scenario was modeled for the Elm Fork WTP, which did not have any active or passive mitigation. The scenario involved a release through 1/8- inch hole created by a leak in a packing valve on a rail car that is occasionally stored outside. It was assumed that this leak could occur for 120 minutes, the time between operator rounds, creating a release rate of 30 lb/min. DEGADIS+ was used to characterize the effects of the alternative case scenario at the Elm Fork WTP. The distance to the toxic endpoint of 3 ppm was determined to be 0.89 miles. The estimated affected residential population is 1,500 people. GENERAL ACCIDENTAL RELEASE PRECAUTION PROGRAM The Elm Fork WTP carries out consistent operation and maintenance of its chlorine equipment utilizing only fully trained personnel in this area. Elm Fork WTP management enforces consistent operation through discipline for operational deviations. FIVE-YEAR ACCIDENT HISTORY The Elm Fork WTP's accident history was reviewed for a period from June 1994, through June 1999. During this period of time, no accidental releases of chlorine had occurred. EMERGENCY RESPONSE PROGR AM As mentioned earlier, this facility has developed an Emergency Response Program in which plant employees are divided into various management and response teams. There are five in-plant contacts for an emergency, the Operations Supervisor, and the Shift Supervisors. There are also back-up personnel in the event that the primary response personnel cannot be contacted. The Emergency Response Plan includes: (1) procedures to follow in the event of a chlorine emergency, (2) information about the frequency of employee emergency response training, and (3) a detailed description of the emergency response training underway. The Dallas County HAZMAT team has been designated to provide back-up emergency responders and equipment, and will assume Incident Command upon arrival to the plan's emergency call. PLANNED CHANGES TO IMPROVE SAFETY Based on the hazard review and prevention evaluation completed for chlorine a list of action items was developed and is being considered by Elm Fork WTP management to determine if implementation is to be accomplished. The most notable planned changes include the following: 7 While the Elm Fork WTP does have a chlorine scrubber, it is not designed to meet the current Uniform Fire Codes. Therefore, the chlorine scrubber design should be upgraded to meet the current standards. Also, establishing a SOP for the routine testing of the concentration of the scrubbing solution should be considered. This would be added to ensure that the strength of the solution is adequate to scrub the contaminated air. 7 Consideration of adding remote sensors and alarms below the car spotting. The consideration of outside leak detection is tied to the periodic need for railcars containing chlorine to be stored on site with some cars inside the chlorine storage area and others (up to two) situated outside of the building. This situation arises periodically and is tied to the inefficient delivery from the railroad. Given that these extra cars were spotted outside, the installation of a leak detection system soul ensure that the leaks would be detected. 7 The evaluation of the need for an automatic kill switch on the tanks. This would be useful in the case of an emergency when the tanks have to be shut off immediately. A remote switch would eliminate the danger of plant personnel having to shut the chlorine tanks off manually. 7 Consideration of acquiring emergency response equipment and training for on-site personnel to decrease the response times. 7 The addition of the expansion chamber valves in the storage area to the exercise program. If this is added to the program, the valves would be exercised regularly and any malfunctions could be detected and repaired before an accident could occur. 7 MW will coordinate with the staff to develop a procedure for how the chlorine truck driver or vendor should perform while on plant grounds. It is anticipated that the vendor can then be subjected to this procedure at the time of the plant's next bid for chemical purchase. However, the existing vendor will likely accept these requirements voluntarily to ensure customer satisfaction. 7 The evaluation of establishing a SOP for inspection and maintenance of the rupture disk and tank in the storage area. Currently, there is no procedure for this and while the current procedure to replace the equipment as needed is adequate the implementation of this SOP could help to prevent any major releases. 7 The consideration of establishing a SOP for routine inspection and maintenance of the ventilation systems. Currently, the Elm Fork WTP has periodic visual inspections of the ductwork; however, there is no set procedure for this. The implementation of a SOP could help prevent an inefficient system. |