Bachman 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 Bachman 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 above the threshold limits specified by the USEPA, there by making the facility subject to compliance with the regulation. The Bachman 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 impacts 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 Bachman WTP. RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The Bachman WTP facility in Dallas, Texas has an excellent record in preventing and minimizing releases of chlorine and ammonia. 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 Bachman WTP uses chlorine combined with ammonia to disinfect water. The Bachman WTP regularly has a maximum storage quantity of 205 tons of chlorine at its facility. The chlorine is stored in two DOT certified 90-ton rail cars and an emergency storage tank. The storage tank has a capacity to store 30 tons of chlorine, but only 25 tons are stored in the tank based on administrative controls. This total amount of chlorine exceeds the threshold limit of 2,500 pounds set by the USEPA. In addi tion to the chlorine stored on-site, the Bachman WTP regularly has a maximum storage quantity of 2,000 gallons, or approximately 10,000 pounds, of ammonia stored in stationary tanks. This amount equals the threshold limit of 10,000 pounds set by the USEPA. PROCESS DESCRIPTION The Bachman WTP receives raw water from Lake Grapevine, Lake Lewisville, and Lake Ray Roberts, by way of the Trinity River, into the treatment plant located at 2605 Shorecrest Drive in Dallas, 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 Bachman WTP consist of (1) inside storage tanks (two 90-ton rail cars and one 30-ton emergency tank), (2) liquid feed piping and miscellaneous valves, (3) two evaporators, (4) gas piping and miscellaneous valves, (5) four chlorinators, and (6) one scrubber system. 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). The majority of chlorine is delivered to the Bachman WTP by railroad on rail spurs and is stored in two 90-ton railroad tank cars, located at the Chlorine and Ammonia Building. A chlorine tanker truck supplies the emergency tank, when necessary. Chlorine is removed as a liquid under pressure from a rail car or the emergency tank. 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 only used when no chlorine is available in either of the rail cars, which is a rare occurrence. The liquid chlorine is pumped through a flexible reinforced hose to two chlorine evaporators located in the chlorine evaporator room. The chlorine gas generated by the evaporators is then transferred to the chlorinators. The chlorine gas is then mixed into solution and is fed to the rapid mix basins, the secondary basins, or the filter outlet. The existing ammonia feed facilities at the Bachman WTP consist of (1) two 1,000-gallon stationary tanks, (2) liquid feed piping and miscellaneous valves, (3) evaporators, (4) gas piping and miscellaneous valves, and (5) 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 Bachman WTP by tanker truck and is stored in the tanks located outside of the Chlorine and Ammonia Building. Ammonia is removed as a liquid under pressure from one tank at a time. As the supply in one 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 to application points at the influent pipe to the rapid mix basins, the secondary rapid mix basins, and the filter influent. WORST-CASE AND ALTERNATIVE RELEASE SCENARIOS The storage and process areas for both ammonia and chlorine have associated hazards that can potentially affect on-site employees and the off-site population and environment. The USEPA requires that a single worst-case release scenario 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 applicable to the w orst-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 Bachman facility. The distance to the toxic endpoint of 3 ppm was determined to be 5.65 miles. The estimated affected residential population is 230,000 people. Commercial, industrial and residential areas would be affected in the worst-case release scenario. Alternate Scenarios One alternate release scenario for chlorine was modeled for the Bachman WTP and did not involve any form of mitigation. The scenario involved a release through a 1/8-inch hole created by a leak in the packing valve on the rail car that is occasionally stored outside. The leak duration was assumed to be 120 minutes, the time between operator rounds, resulting in a release rate of 30 pounds per minute. DEGADIS+ was used to characterize the effects of the alternate release scenario for chlorine at the Bachman WTP. The distance to the toxic endpoint of 3 ppm was determined to be 0.54 miles. The estimated affected residential population is 340 people. Two alternate release scenarios for ammonia were modeled for the Bachman WTP, neither of which had any active or passive mitigation. The first alternate release scenario for ammonia could occur because of damage to the line near the storage tank. A release of ammonia through a =-inch diameter hole would last for about 10 minutes and yield a release rate of 326 pounds per minute. DEGADIS+ was also used to characterize the effects of the alternate release scenario for ammonia at the Bachman WTP. The distance to the USEPA defined toxic endpoint of 200 ppm was determined to be 0.6 miles. The estimated affected residential population is 530 people. The second alternate release scenario for ammonia involved a release through a leak in the discharge line caused by a faulty valve or defective threads. The release could occur through a 1/8-inch hole and would last for about 2 hours, the maximum time between operator rounds. 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 0.12 miles. The estimated affected residential population is 4 people. GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAM The Bachman WTP carries out consistent operation and maintenance of its chlorine and ammonia equipment, utilizing only fully trained personnel in these areas. Bachman WTP management ensures consistent operation by using disciplinary measures for operational deviations. FIVE-YEAR ACCIDENT HISTORY The accident history for the Bachman 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 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. 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 chlorine and ammonia, a list of action items was developed and is being considered by Bachman WTP management to implement, if feasible. The most notable planned changes include the following: 7 Consider implementing a procedure, d eveloped in conjunction with MW, to require inspection of a rail car once it is spotted on-site. After the railroad personnel leave the rail car on-site, the car is currently left unattended until Bachman WTP personnel move the rail car into the building. A procedure would reduce the uncertainty associated with an uninspected rail car being left on-site; 7 Consider outside leak detection for the chlorine rail cars. Periodically, rail cars containing chlorine need to be stored on site, with some cars placed inside the Chlorine and Ammonia Building and others (up to two) situated outside of the building. This situation occurs because of the sporadic supply from the railroad (in the past, the plant has waited as long as 45 days to receive a rail car of chlorine). Because extra cars may be spotted outside, the installation of a leak detection system should ensure the detection of any leak; 7 Ensure that the delivery drivers follow set procedures when delivering either ammonia or c hlorine. MW will coordinate with the staff to develop a procedure to govern the activities of the 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 Currently, the ammonia tanks are located outside without any insulation, containment or surrounding barriers. Insulation might eliminate the feed problems currently experienced during the winter. If the tanks were enclosed, insulation would not be required but a scrubbing system would be needed. The scrubbing system would contain and neutralize the ammonia gas to prevent accidental releases into the atmosphere. Many factors govern the designs of a containment building and a scrubber system, such as size, applicable regulation compliance, location and cost. Because these are major expenses, budgets are needed. Therefore, the Bachman WTP will investigate the design, cost and benefit of an ammonia scrubber system during 1999. |