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 ammonia. The amount of ammonia stored is well above the threshold limit specified by the USEPA thereby making the facilit y 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 ammonia. This facility is implementi ng 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 ammonia to form chloramines as a disinfectant in the water treatment process. The Elm Fork WTP regularly has a storage maximum quantity of 34 tons of ammonia at its facility that is stored in stationary tanks. This is above the threshold limit (10,00 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, in Carrollton, Texas. Water is treated at the plant a nd subsequently pumped to the distribution network of pipelines, pump stations, and storage tanks. The existing ammonia feed facility at the Elm Fork WTP consists of (1) two 20-ton stationary tanks, (2) liquid feed piping and miscellaneous valves, (3) evaporators, (4) gas piping and miscellaneous valves, (5) ammoniators, and (6) an ammonia scrubber system. On treatment plant grounds, the two areas in which ammonia has a potential to generate a gaseous release are the ammonia storage area (items 1 and 2 above) and the ammonia process areas (items 3 through 6 above). Ammonia is delivered to the Elm Fork WTP by tanker truck and stored in the tanks located inside the storage building. Ammonia is removed as a liquid and is withdrawn from one tank at a time. As the supply in one rail car empties, the supply is manually valved to the full tank. The ammonia is hard-piped to the ammonia evaporators located in the ammonia evaporator room. The ammonia gas generated by the evaporator is then transferred to the ammoniators that feed to the application points at valve vault A or B (the influent pipe to the rapid mix basins) and after filtration. WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS The ammonia 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 chemical. Worst-Case Scenario The largest potential release of ammonia would occur through a valve failure on the stationary tank located inside the building. Under Section 68.25(c)(1), the release time for a chemical such as ammonia is 10 minutes. It was assumed that the scrubber was not functional, but mitigation was applicable to the worst-case release because it would occur inside. 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 200 ppm was determined to be 1.49 miles. The estimated affected residential population is 7,800 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 release could occur during filling of the ammonia tanks. The tank truck could drift causing the tank truck fill line to break. A release of ammonia through a 1-inch diameter hole would occur for about 10 minutes. The release rate of ammonia caused by leakage through this opening is calculated to be 30 lb/min. DEGADIS+ was also used to characterize the effects of the alternative case scenario at the Elm Fork WTP. The distance to the USEPA defined toxic endpoint of 200 ppm was determined to be 1.24 miles. The estimated affected residential population is 4,600 people. GENERAL ACCIDENTAL RELE ASE PRECAUTION PROGRAM The Elm Fork WTP carries out consistent operation and maintenance of its ammonia 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 ammonia had occurred. EMERGENCY RESPONSE PROGRAM 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 ammonia emergency, (2) information about the frequency of employee emergency response training, and (3) a detailed description of the emergency response training underway. The City of Dallas 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 ammonia 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 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 ammonia tanks off manually. 7 Ensure that the delivery driver follows a set procedure in the delivery of ammonia. MW will coordinate with the staff to develop a procedure for how the ammonia 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 consideration of establishing a SOP for inspection and maintenance of the rupture disk and tank and other process equipment 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 p revent an inefficient system. |