East Side WTP - Executive Summary |
|
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 East Side Water Treatment Plant (East Side 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 facility subject to compliance with the regulation. The East Side 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 East Side WTP. RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The East Side WTP facility in Sunnyvale, Texas has an excellent record in preventing and minimizing releases of ammonia. This facility is implementing 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 Dallas County Fire Department and 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 Dallas County Fire Department HAZMAT team. REGULATED SUBSTANCE The East Side WTP mixes ammonia with chlorine to form chloramines as a disinfectant in the water treatment process. The East Side WTP regularly has a storage maximum quantity of 6,000 gallons of ammonia at its facility that is stored in stationary tanks. This is above the threshold limit of 10,000 pounds set by the USEPA. PROCESS DESCRIPTION The East Side WTP receives raw water from Lake Tawakoni and Lake Ray Hubbard into the treatment pl ant located at 405 Long Creek Road, in Sunnyvale, Texas. Water is treated at the plant and subsequently pumped to the distribution network of pipelines, pump stations, and storage tanks. The existing ammonia feed facility at the East Side WTP consists of (1) three 2,000-gallon stationary tanks, (2) liquid feed piping and miscellaneous valves, (3) three evaporators, (4) gas piping and miscellaneous valves, and (5) seven ammoniators. 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 5 above). Ammonia is delivered to the East Side WTP by truck and stored in the tanks located at the Chemical Building. Ammonia is removed as a liquid under pressure of the storage tank. Ammonia is withdrawn from one tank at a time. As the supply in one storage tank empties, the supply is manually switched to the full tank. The ammonia is hard-pipe d to the ammonia evaporators located in the ammonia evaporator room. The ammonia gas generated by the evaporator is then transferred to the ammoniators and can feed either to the flash mixers or the injection vault next to TPS #1. 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 2,000-gallon tank located on the north side of the plant. This valve failure could potentially release all 2,000 gallons of the ammonia as a gas. Under Section 68.25(c)(1), the release time for a chemical such as ammonia is 10 minutes. Passive mitigation controls were not 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 East Side facility. The distance to the toxic endpoint of 200 ppm was determined to be 1.15 miles. The estimated affected residential population is 2,300 people. Commercial/industrial areas and residential areas would be affected in the worst-case release scenario. Alternate Scenario Two alternate scenarios were modeled for the East Side WTP, neither of which had any active or passive mitigation. The first release could occur because of damage to the pressure release valve on the discharge pipe. A release of ammonia through a 1/8-inch diameter hole would occur for about 2 hours, the maximum time between operator rounds. The release rate of ammonia caused by leakage through this opening is calculated to be 21 lb/min. DEGADIS+ was also used to characterize the effects of the alternative case scenario at the East Side WTP. The distance to the USEPA defined toxic endpoin t of 200 ppm was determined to be 0.09 miles. The estimated affected residential population is 6 people. The second scenario involves a release through 1/4-inch hole created by a leak in a packing valve. It was assumed that this leak could occur for 60 minutes. DEGADIS+ was used to characterize the effects of the alternative case scenario at the East Side WTP. The distance to the toxic endpoint of 200 ppm was determined to be 0.21 miles. The estimated affected residential population is 33 people. GENERAL ACCIDENTAL RELEASE PRECAUTION PROGRAM The East Side WTP carries out consistent operation and maintenance of its ammonia equipment utilizing only fully trained personnel in this area. East Side WTP management enforces consistent operation through discipline for operational deviations. FIVE-YEAR ACCIDENT HISTORY The East Side 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 ha d 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 plant'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 develop ed and is being considered by East Side WTP management to determine if implementation is to be accomplished. The most notable planned changes include the following: 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 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 The identification of security improvement. The security system at East Side should be upgraded to restri ct access through a remotely operated gate system or card system. 7 The consideration of the need for an automatic kill switches 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 Emergency shutdown procedures should be developed and implemented in the training sessions. 7 The East Side WTP is currently under design for improvement to the chemical handling system. These improvements include complete containment and chemical neutralization of accidental releases of ammonia through scrubbing. The plant's management anticipates these improvements to be completed within the next three years. |