Bureau of Reclamation - Yuma Area Office - Executive Summary |
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EXECUTIVE SUMMARY The Bureau of Reclamation - Yuma Area Office accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. All applicable procedures of the EPA Prevention Program are adhered to. The Bureau of Reclamation - Yuma Area Office emergency response policy involves the preparation of response plans which are tailored to the facility and to the emergency response services available in the community, and is in compliance with the EPA Emergency Response Program requirements. The Bureau of Reclamation - Yuma Area Office is a water desalting plant using chlorine for disinfection purposes. The facility contains chlorine in two storage tanks. The storage vessels, piping, pumps, and various other equipment are interconnected within the storage area. The storage vessels capacities at the facility include two one-ton tanks. The station is usually unmanned unless utilized. Operators visit the station daily and respond to any problems and alarms as they may occur. The offsite consequence analysis includes consideration of two chlorine release scenarios, identified as "worst case release" and "alternative release scenario." The first scenario is defined by the EPA, which states that "the owner or operator shall assume that the ... maximum quantity in the largest vessel ... is released as a gas over 10 minutes," due to an unspecified failure. The alternative release scenario is one that is "more likely to occur than the worst case release scenario." Atmospheric dispersion modeling has to be performed to determine the distance traveled by the chlorine released before its concentration decreases to the "toxic endpoint" selected by the EPA of 0.14 mg/L, which is the Emergency Response Planning Guideline Level 2 (ERPG-2). This is defined by the American Industrial Hygiene Association (AIHA) as the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without which could impair an individual's ability to take protective action." The residential population within a radius corresponding to the toxic endpoint distance has to be defined, "to estimate the population potentially affected." The worst case release scenario at The Bureau of Reclamation - Yuma Area Office involves a failure of the lines and all mitigation systems within the station between any of the tanks for Process 1. Because all the tanks, pipes, pumps, and equipment are interconnected, the total amount of chlorine that potentially could be released would amass to approximately 4,000 lbs. The offsite consequence analysis for this scenario was performed for two sets of conditions. The first set followed conditions pre-defined by the EPA, namely release of the entire amount as a gas in 10 minutes, use of the one hour average ERPG-2 as the toxic endpoint, and consideration of the population residing within a full circle with radius correspo nding to the toxic endpoint distance. EPA set these conditions to facilitate the performance of the offsite consequence analysis; however, the assumptions used are unrealistic because: Only the population within an elliptical plume extending downwind of a release point is potentially affected. This plume, or footprint, is approximately 6% (one-twentieth) of the area of the full circle. It is not appropriate to compare a 10-minute release to a one hour average standard. The one hour ERPG value can be modified using available time of exposure/concentration relationships to match the ten minute release time. When atmospheric dispersion modeling for the worst case scenario was performed using the EPA assumptions, a distance to toxic endpoint of 4.2 miles and an estimate of residential population potentially affected of approximately 15,000 was obtained, as a result the Yucca Power Plant, Cocopah R.V. Golf and Resort, and the surrounding area were encompassed. The alternative rel ease scenario involved the rupture of a tank possibly due to vehicular damage or vandalism. The amount of chlorine released was predicted to be 20 lbs/min and toxic endpoint distances from ERPG-2 were obtained. The latter is defined by AIHA as "the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing life-threatening health effects." The typical meteorological conditions used were a Stability Class D, wind speed 3.0 m/s, average air temperature, and average humidity. The estimated distances traveled to the toxic endpoints was 0.2 miles for the ERPG-2. The general DWP accidental release prevention program is based on the following key elements: High level of training of the operators. Preventative maintenance program. Use of state-of-the-art process and safety equipment. Use of accurate and effective operating procedures, written with the participation of the operators. Performance of a hazard review of equipment and procedures. Implementation of an auditing and inspection program. Chemical specific prevention steps include availability of self-contained breathing apparatus (SCBA), worn by the operators during connection/disconnection of chlorine supply, and awareness of the hazardous and toxic properties of chlorine. No accidental releases of chlorine have occurred at this facility in the past five years. The facility is subject to the Program 3 requirements for federal regulations as assessed from the Process Hazard Evaluation and the following reasons: The distance to a toxic substance endpoint for a worst case release is greater than the distance to a public receptor. The facility Standard Industrial Code (SIC) Classification is 9511 The facility North American Industrial Classification System (NAICS) number is 92119 The facility has an emergency response program, which has been coordinated (reviewed) by the City of Yuma Fire Depar tment, which is a member of the Local Emergency Response Planning Committee (LEPC). This program includes an emergency response decision tree and a notification plan. Emergency response drills and drill evaluations are conducted once every year; emergency operations and response procedures are also reviewed at that time. |