Bachman Water Treatment Plant - Executive Summary
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 ammonia. The amount of ammonia stored is at the threshold limit specified by the USEPA thereby 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 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 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 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 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 City of Dallas HAZMAT team.
The Bachman WTP mixes ammonia with chlorine to form chloramines as a disinfectant in the water treatment process. The Bachman WTP regularly has a storage maximum quantity of 2,000 gallons, approximately 10,000 pounds, of ammonia at its facility that is stored in stationary tanks. This at the threshold limit of 10,000 pounds set by the USEPA.
The Bachman WTP receives raw water from Lake Grapevine, Lake Lewisville, and Lake Ray Hubbard by way of the Trinity River into the treatment pl
ant 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 ammonia feed facility at the Bachman WTP consists 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) chlorinators. 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 Bachman WTP by tanker truck and stored in the tanks located outside of the Chlorine and Ammonia Building. Ammonia is withdrawn from one tank at a time. As the supply in one tank empties, the supply is manually switched to the full tank.
The ammonia is hard-piped to the ammonia evaporators located in the ammonia evaporator roo
m. The ammonia gas generated by the evaporator is then transferred to the ammoniators that feed to the application points at the influent pipe to the rapid mix basins, the secondary rapid mix basins, and prior to the filters
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.
The largest potential release of ammonia would occur through a valve failure on the 1,000-gallon tank located on the north side of the plant. This valve failure could potentially release all 1,000 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.
pproved modeling program DEGADIS+ was used to characterize the effects of the worst case scenario at the Bachman facility. The distance to the toxic endpoint of 200 ppm was determined to be 0.69 miles. The estimated affected residential population is 970 people. Commercial/industrial areas and residential areas would be affected in the worst-case release scenario.
Two alternate scenarios were modeled for the Bachman WTP, neither of which had any active or passive mitigation. The first release could occur because of damage to the line near the storage tank. A release of ammonia through a =-inch diameter hole would occur for about 10 minutes. The release rate of ammonia caused by leakage through this opening is calculated to be 326 lb/min. DEGADIS+ was also used to characterize the effects of the alternative case scenario 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 res
idential population is 530 people.
The second scenario involves a release through a leak in the discharge line due to a faulty valve or threads. The release could occur through a 1/8-inch hole and would occur for about 2 hours, the maximum time between operator rounds. DEGADIS+ was used to characterize the effects of the alternative case scenario at the Bachman WTP. 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 PRECAUTION PROGRAM
The Bachman WTP carries out consistent operation and maintenance of its ammonia equipment utilizing only fully trained personnel in this area. Bachman WTP management enforces consistent operation through discipline for operational deviations.
FIVE-YEAR ACCIDENT HISTORY
The Bachman 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 o
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 a
nd is being considered by Bachman WTP management to determine if implementation is to be accomplished. The most notable planned changes include the following:
7 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 Currently, the ammonia tanks are located outside with no containment or barrier surrounding them. If the tanks were insulated, the plant would not have the feed problems during the winter. However, the tanks would not need to be insulated if the tanks were enclosed, but a scrubbing system would most likely need to be added. The purpose of the scrubber would be to contain and neutralize the ammonia gas to prevent accidental releases into the a
tmosphere. Many factors go into the design of a containment building and a scrubber system (size, applicable regulation compliance, location, cost, etc.) and being a major expense, has to be budgeted for. Therefore the Bachman WTP will investigate the design, cost and benefit of an ammonia scrubber system during 1999. A review of the regulatory acceptability of ammonia as it relates to scrubbing has been conducted in the prevention section of this report.