Rio Grande City Wastewater Treatment Plant - Executive Summary |
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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 the accidental release of hazardous substances. The Risk Management Program Rule addresses over 100 chemical substances, 77 of which are acutely toxic and 63 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 Rio Grande City Wastewater Treatment Plant (WWTP) falls under this regulation because of the on-site storage of chlorine. The amount of chlorine stored is above the threshold limit specified by the USEPA thereby making the facility subj ect to compliance with the regulation. Rio Grande City personnel have complied with the USEPA Risk Management Program rule and have completed an Accidental Release Program Plan (ARPP) that contains the following required information: Management System A hazards assessment that establishes the worst case and alternate release scenarios and their impact on the population and the environment (40 CFR Subpart B) A prevention program that includes safety information, a hazards review, operating procedures, training, maintenance, compliance audits and incident investigation (40 CFR Subpart C) An emergency response plan (40 CFR Part 68 Subpart E) The following subsections discuss details of the plan that has been implemented at the Rio Grande City Wastewater Treatment Plant. RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES The Wastwater Treatment Plant facility in Rio Grande City, Texas has an excellent record in preventing and minimizing releases of chlorine. The emergency respons e policies at this facility ensure that there is emergency response coverage 24 hours a day, 7 days per week. There are also adequate provisions for coordination with outside agencies, such as Rio Grande City Fire Department in the event of an emergency. In the event of a release, plant staff will contact the Rio Grande City Fire Department, relaying information regarding the release prior to implementing plant evacuation to a location outside the plant gates, awaiting the fire department to inform its personnel of all information about the release and to provide assurance that the plant has been totally evacuated. REGULATED SUBSTANCES The wastewater treatment plant uses chlorine as a disinfectant in the wastewater treatment process. The plant regularly has a storage maximum quantity of 2 one-ton cylinders of chlorine at its facility that is stored outside. This is above the threshold limit of 2,500 pounds set by the EPA. PROCESS DESCRIPTION The wastewater treatment plant is lo cated on the Fort Ringold Campus, Rio Grande City, Texas and on the banks of the Rio Grande River. The wastewater is treated at the plant and subsequently discharged into the Rio Grande River. The existing chlorine feed facility at the wastewater treatment plant consists of (1) 2 one-ton chlorine containers, (2) two vacuum regulators mounted to an automatic switchover module with gas piping and miscellaneous valves, (3) flow poportionate feed chlorinators and (4) gas piping and ejectors. On the treatment plant grounds, the only area in which chlorine has a potential to generate a gaseous release is the chlorine storage area ( items 1 and 2 above). Chlorine is delivered to the wastewater treatment plant by truck and chlorine containers are stored in the outside storage area located to the west of the Chemical Building. Chlorine is removed as a gas under pressure from the liquid in the individual containers, however, the majority of the chlorine feed is operated through a water injec tion induced vacuum, making the system extremely safe and minimizing potential pressurized leaks along the feed lines. WORST CASE AND ALTERNATIVE RELEASE SCENARIOS The chlorine storage and process areas have associated hazards that can potentially affect on-site employees and the off-site population and environment. The EPA requires that one worst case scenario and on alternate release scenario is reported for each regulated chemical. WORST CASE SCENARIO The largest potential release of chlorine would have occured through a valve failure on one of the one-ton cylinders located at the plant. This valve failure could potentially release all 2,000 pounds of the 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 modeling program "RMP Comp" was used to characterize the effects of the worst case scenario at the wastewater treatm ent plant facility. The distance to the toxic endpoint of 3 ppm was determined to be a radius of 1.3 miles from the release. The estimated affected residential population is 10,000 people. School, residential and Commercial/Industrial areas would be affected in the worst case release scenario. The worst case scenario release would also affect two high volume roadways (US 83 & FM 755) and an International Bridge (Rio Grande City/Camargo) crossing. Additionally, the toxic endpoint distance carried over the international boundary of the Rio Grande River into Mexico. The specific affects to population and environment were not determined but can be assumed to be similar to those on the United States side of the border. The Accidental Release Prevention Program plan will include provisions and procedures for alerting the proper Mexican officials in the event of a release. ALTERNATE SCENARIO One alternate scenario was modeled for the wastewater treatment plant. The release was est ablished as a leak that would potentially develop in the packing at the chlorine container valve. A release of chlorine through a 1/5 inch diameter hole in the valve packing would occur for about 10 minutes and is presummed to be observed or detected. The release rate of chlorine caused by the leakage through this opening is calculated to be 73.7 pounds per minute. "RMP Comp" was also used to model the effects of the alternative case scenario at the wastewater treatment plant. The distance to the EPA defined toxic endpoint of 3 ppm was determined to be a radius of 0.3 miles from the release. The estimated affected population is 4,000 people. The distance to the toxic endpoint for the alternate release scenario also carried over the international boundary of the Rio Grande River into Mexico. The Accidental Release Prevention Program plan will include provisions and procedures for alerting the proper Mexican officials in the event of a release. GENERAL ACCIDENTAL RELEASE PRECAU TION PROGRAM The Rio Grande City Wastewater Treatment Plant carries out consistent operation and maintenance of its chlorine equipment utilizing only fully trained personnel in this area. The wastewater treatment plant management enforces consistent operation through monitoring and discipline for operational deviation. FIVE YEAR ACCIDENT HISTORY The Rio Grande City Wastewater Treatment Plant's accident history was reviewed from December 1994 to December 1999. During this period, no accidental releases of chlorine had occured. EMERGENCY RESPONSE PROGRAM This facility has developed and Emergency Response Program involving the immediate plant evacuation once the City's Fire Department is called to implement response and repair to leaking chlorine gas. The plant is staffed 24 hours per day, 7 days a week. Plant operators are required to make rounds for inspection and monitoring of the plants processes every hour. Accordingly, plant staff will detect any releases of chlorine and t he Fire Department is trained to respond to this situation. The Emergency Response Plan includes: (1) procedures to follow in the event of a chlorine emergency, (2) information about the plants evacuation plan and (3) a detailed description for the emergency responders plan for handling such an emergency. The Rio Grande City Fire Department has been designated to provide emergency responders and equipment, and will assume Incident Command upon arrival to the plant's emergency. PLANNED CHANGES TO IMPROVE SAFETY Based on the hazards review and prevention evaluation completed for chlorine, a list of action items was developed and is being considered by Rio Grande City's Wastewater Treatment Plant management to determine if and how implementation is to be accomplished. The most notable planned changes include the following: Ensure that the delivery driver follows a set procedure in the delivery of chlorine. Alphamerican Engineering will coordinate with the staff to develop a procedu re for how the chlorine vendor's truck driver should perform while on plant grounds. It is anticipated that the vendor can be required to follow this procedure at the time of the plant's next bid for chemical purchase. The existing vendor will likely accept these procedures voluntarily to ensure customer satisfaction. The consideration of remote leak detection for chlorine gas in the chlorine storage area and in the chlorinator building as a warning of vacuum regulator failure and as a back up sensor. Provide back up power for the plant in the event of a power outage. In the future, when the plant facilities are expanded or upgraded, consideration should be given to design and construction of a containment building to house the chlorine cylinders and designed in conjunction with the capability to chemically neutralize any accidental release of chlorine. This option might be compared with the conversion to a nongaseous chlorine compound. |