East Side WTP - 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 East Side Water Treatment Plant (WTP) falls under this regulation because of the on-site storage of chlorine and ammonia. The amounts stored for both chemicals are well above the threshold limits 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 A management system (40 CFR Part 68 Subpart A); 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); and 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 preventin g and minimizing releases of ammonia and chlorine. The emergency response policies at this facility ensure that emergency response coverage is available 24 hours per day, 7 days per week. Adequate provisions have been implemented to coordinate response activities with outside agencies, such as the City of Dallas HAZMAT team, in the event of an emergency. The plant staff will receive training to enable an on-site staff response prior to the arrival of the City of Dallas HAZMAT team. REGULATED SUBSTANCE The East Side WTP uses chlorine combined with ammonia to disinfect water. The East Side WTP regularly has a maximum storage quantity of 180 tons of chlorine at its facility. The chlorine is stored in two DOT certified 90-ton rail cars. This amount of chlorine exceeds the threshold limit of 2,500 pounds set by the USEPA. In addition to the chlorine stored on-site, the East Side WTP regularly has a maximum storage quantity of 6,000 gallons of ammonia stored in stationary tanks. This amount exceeds the threshold limit of 10,000 pounds set by the USEPA. PROCESS DESCRIPTION The East Side WTP receives raw water from the City of Dallas' East Texas water supply, Lake Tawakoni and Lake Ray Hubbard into the treatment plant 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 chlorine feed facilities at the East Side WTP consist of (1) two 90-ton rail cars, (2) liquid feed piping and miscellaneous valves, (3) three evaporators, (4) gas piping and miscellaneous valves, (5) three pre-chlorinators, and (6) three post-chlorinators. A release of chlorine gas could potentially occur at the chlorine storage area (items 1 and 2 above) and at the chlorine process areas (items 3 through 6 above). Chlorine is delivered to the East Side WTP by railroad on rail spurs and is stored in two 90-ton railroad tank cars, which are located north of the Chemical Building. Chlorine is removed as a liquid under pressure from a rail car. 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 liquid chlorine is pumped through a flexible reinforced Monel hose to three chlorine evaporators located in the chlorine evaporator room. The chlorine gas generated by the evaporators is then transferred to three pre-chlorinators that feed either to the forebay or to the raw water junction. Additionally, chlorine gas can be transferred to three post-chlorinators that feed to the transfer pump station suction flumes. The existing ammonia feed facilities at the East Side WTP consist 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. A release of ammonia gas could potentially occur at the ammonia storage area (items 1 and 2 above) and at the ammonia process areas (items 3 through 5 above). Ammonia is delivered to the East Side WTP by truck and is stored in the tanks located outside the Chemical Building. Ammonia is removed as a liquid under pressure and is withdrawn from one storage tank at a time. As the supply in one storage tank empties, the supply is manually switched to the full tank. The liquid ammonia is delivered to the ammonia evaporators located in the ammonia evaporator room. The ammonia gas generated by the evaporators is then transferred to the ammoniators that feed either to the flash mixers or to the injection vault, located next to Transfer Pump Station Number One. WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS The storage and process areas for both chlorine and ammonia have associated hazards that can potentially affect on-site employees and the off-site population and environment. The USEPA requires that one worst-case release sc enario for the facility and one alternate release scenario for each regulated chemical be reported. Worst-Case Scenario The worst-case release scenario that creates the greatest distance in any direction to an endpoint offsite involves a chlorine release. 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 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 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 release scenario at the East Side facility. The distance to the toxic endpoint of 3 ppm was determined to be 8.58 miles. The estimated affected residential population is 230,000 people. Commercial, industrial and residential ar eas would be affected in the worst-case release scenario. Alternate Scenarios Two alternate release scenarios for chlorine were modeled for the East Side WTP, neither of which had any form of mitigation. The first alternate release scenario for chlorine could occur because of damage to the flex hose leading from the rail car. A release of chlorine through a 1-inch diameter hole would last for 10 minutes, yielding a release rate of 1,842 pounds per minute. DEGADIS+ was also used to characterize the effects of this alternate release scenario at the East Side WTP. The distance to the USEPA defined toxic endpoint of 3 ppm was determined to be 5.53 miles. The estimated affected residential population is 70,000 people. The second alternate release scenario for chlorine involved a release through a 1/8-inch hole created by a leak in the packing valve. The leak duration was assumed to be 120 minutes, the time between operator rounds, resulting in a release rate of 30 pounds per min ute. DEGADIS+ was again used to characterize the effects of the alternate release scenario at the East Side WTP. The distance to the toxic endpoint of 3 ppm was determined to be 0.44 miles. The estimated affected residential population is 140 people. Two alternate release scenarios were also modeled for ammonia at the East Side WTP. Neither scenario had any form of mitigation. The first alternate release scenario for ammonia 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 last for about 2 hours, the maximum time between operator rounds, yielding a release rate of 21 pounds per minute. DEGADIS+ was again used to characterize the effects of the alternate release scenario at the East Side WTP. The distance to the USEPA defined toxic endpoint of 200 ppm was determined to be 0.09 miles. The estimated affected residential population is 6 people. The second alternate release scenario f or ammonia involved a release through a 1/4-inch hole created by a leak in the packing valve. The leak duration was assumed to be 60 minutes. DEGADIS+ was used to characterize the effects of this alternative case scenario as well. 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 PREVENTION PROGRAM The East Side WTP carries out consistent operation and maintenance of its chlorine and ammonia equipment, utilizing only fully trained personnel in these areas. East Side WTP management ensures consistent operation by using disciplinary measures for operational deviations. FIVE-YEAR ACCIDENT HISTORY The accident history for the East Side WTP was reviewed for the period from June 1994 through June 1999. During this period of time, no accidental releases of chlorine or ammonia had occurred. EMERGENCY RESPONSE PROGRAM As mentioned earlier, this facility has develop ed 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. Back-up personnel are available in the event that the primary response personnel cannot be contacted. The Emergency Response Plan includes: (1) procedures to follow in the event of either a chlorine or 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 at the plant. PLANNED CHANGES TO IMPROVE SAFETY Based on the hazard reviews and prevention evaluations completed for both ammonia and chlorine, a list of action items was developed and is being considered by East Side WTP management to implement, if feasible. The most notable planned changes include the following: 7 Evaluate the need to develop a tank inspection program. Usually the railroad company will leave a new rail car on-site, away from the chlorine tower, until notified by East Side personnel to move it closer to the tower. If a procedure was implemented that required a rail car to be inspected once spotted on-site, the uncertainty of detecting a leak on a rail car stored away from the tower would be alleviated; 7 Post a copy of the procedure for tank hook-up and disconnection by the chlorine tree, in a Plexiglas frame. This procedure would eliminate any confusion that the operators might have about the disconnection and hook-up processes; 7 Evaluate the need to upgrade the security system to restrict access through a remotely operated gate system or card system; 7 Evaluate the need for automatic kill switches on the tanks. These switches would be useful during an emergency if the tanks had to be shut off imme diately. Remote switches also eliminate the danger of plant personnel having to manually shutdown the chlorine and ammonia systems; 7 Evaluate the need for remote leak detection of the rail cars. For at least the next three years, the rail cars will continue to be stored without containment. Leak detection located between the two rail cars at ground level could immediately provide an audio and visual signal if a leak was detected in the rail car area; 7 The East Side WTP is currently under design for improvements to the chemical handling system. These improvements include complete containment and chemical neutralization of accidental releases of both chlorine and ammonia through scrubbing. The plant's management anticipates these improvements to be completed within the next three years; 7 Emergency shutdown procedures should be developed and implemented in the training sessions; 7 Ensure that the delivery driver follows a set procedure when delivering ammonia. MW will coordin ate with the staff to develop a procedure to govern the activities of the ammonia truck driver or vendor 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. The existing vendor will likely accept these requirements voluntarily to ensure customer satisfaction; and 7 Consider adding the expansion chamber valves in the chlorine and ammonia storage areas to the existing valve exercise program. If added to the program, the valves would be exercised regularly and any malfunctions could be detected and repaired before an accident could occur. |