KCWA ID4 Water Purification Plant - Executive Summary |
|
Facility Description: The Kern County Water Agency (KCWA) uses chlorine at the ID4 Water Purification Plant for water treatment, bacterial and viral destruction, taste and odor control, and to control slime and algae growth. Multiple feed points are provided to give flexibility in achieving disinfection goals. Disinfection is achieved by withdrawing gaseous chlorine from ton cylinders, and metering it through a chlorinator under vacuum created by an injector. The chlorine residual is automatically maintained and its value is continuously recorded. Normally, two cylinders, which rest on the scale, feed the system through one of two pipe manifolds. Up to four cylinders can feed simultaneously through the two manifolds. Typically, an additional six cylinders are stored at the facility. An underhung bridge crane is used for handling cylinders. The chlorine hoist and trolley has a two-ton capacity. Each manifold pipe includes an expansion chamber with a rupture disc. In the event the lin e is valved off and sufficient heat is present, the rupture disc is designed to burst to protect the piping. The expansion tank is sized according to the pipe size and length to contain the pipe contents at a safe pressure. This prevents chlorine from escaping to the atmosphere. A pressure switch is located above the rupture disc to annunciate an alarm in the event of a rupture. A separate alarm is annunciated if the pressure in the gas piping exceeds pre-set limits. Feed equipment consists of chlorinators to meter the gas under vacuum and injectors to create the vacuum and mix the gas with water for transport and application. The system is under vacuum from the ejector to the remote vacuum regulator. From the remote vacuum regulator to the ton cylinder, the system is pressurized. Two chlorine leak detectors are provided in the chlorine storage room and one in the chlorination room. Warning lights are installed near each entry to the chlorination room and the chlorine storage room. K CWA is considering the installation of an alarm annunciator and rotating beacon. Chemicals Subject To EPA's Accidental Release Prevention Program: KCWA uses chlorine at the ID4 Water Purification Plant in quantities large enough to trigger the EPA's Accidental Release Prevention Program. Chlorine is transported to the facility by truck, stored onsite in one-ton cylinders, and used for water disinfection. Accidental Releases During Past Five Years: The KCWA facility has not had any releases during the past five years that resulted in any injuries, off-site evacuations, or property damage. Process Safety Management Accident Prevention Program: The KCWA ID4 Water Purification Plant is subject to OSHA's Process Safety Management (PSM) regulations for all equipment and operations associated with chlorine storage and disinfection systems. KCWA's PSM programs include the following stringent activities to minimize the potential for an accidental release: 7 Review of the design of all eq uipment and controls for the chlorine storage and disinfection systems to ensure they are properly designed and installed. 7 Updating of standard operating procedures to include specific information on safety procedures. All procedures must be reviewed and certified annually. 7 Initial safety training and 3-year refresher training for all operators and maintenance staff. 7 Procedures to ensure that all contractors receive the same safety training that KCWA provides for its own employees. 7 Regular inspection of all equipment, monitoring systems and controls, with stringent documentation of all inspections. 7 Prompt corrective action for any non-conforming items identified by the regular inspections. 7 Rigorous safety reviews conducted prior to system startup, if any equipment or operations are modified. 7 Stringent investigation of any incidents that have the potential to have caused chlorine releases. 7 Periodic evaluation of the safety records of all outside contractors who w ork on the RMP-regulated systems. 7 Development of an effective emergency response program. 7 Implementation of an employee participation program to ensure that all plant-wide staff are aware of the PSM program, and are actively consulted regarding safety issues. 7 Independent audits of the entire PSM program and RMP program every three years. Emergency Response Procedures: KCWA uses its Emergency Response Guidebook to provide step-by-step procedures for emergency response in the unlikely event of an accidental release. The key elements of KCWA's emergency preparedness program are as follows: 7 All plant staff (including administrative and clerical staff) are trained in the specific elements of the program. 7 A team of supervisors and operators are trained, certified and equipped for hazardous materials (Hazmat) emergency operations to repair accidental releases. 7 The plant uses a combination of audible alarms and a plant loudspeaker system to alert the staff of a potential ac cident and to conduct in-plant communications. 7 In the event of a large release, the facility would immediately contact a telephone call-down list that includes the local fire department. KCWA's Recent Steps to Improve Safety: Based on recent safety reviews that were conducted as part of the evaluations for EPA's Accidental Release Prevention Program, KCWA has implemented the following actions to either reduce the likelihood or severity of potential chemical releases: Future Discontinuation of Chlorine Usage - KCWA is proceeding to convert the gaseous chlorine disinfection system to a disinfection system using hypochlorite. Once the new system is installed in 2000, the facility will no longer use gaseous chlorine. A release of hypochlorite solution will be substantially less of a risk than a release of chlorine gas. Installation of Perimeter Security System - KCWA is proceeding with installation of a plant-wide perimeter security system to minimize the threat of vandalism and sab otage. Improved Traffic Protection - KCWA evaluated potential traffic accidents that could damage the chlorine storage area, and will mark and maintain a minimum vehicle traffic distance from the chlorine storage building to reduce the likelihood of accidents. Hypothetical Accidental Release Scenarios: The Risk Management Plan must assess the downwind impacts of hypothetical accidental releases. EPA requires facilities to model the distance that a plume of released gas would travel before it dispersed to an ambient concentration equal to the "Toxic Endpoint Concentration". The Toxic Endpoint Concentrations for various compounds were specified by EPA, and are generally concentrations that would cause no physical harm but could interfere with people's ability to leave the area. The Toxic Endpoint Concentration for chlorine is 3 parts per million (ppm). KCWA conducted a process hazard analysis (PHA), which included an evaluation of potential chlorine release scenarios. In accordance with EPA's rule, two general types of hypothetical accidental release scenarios were developed: 7 The "Administrative Worst-Case Release" that arbitrarily assumes the entire contents of the largest container of chemical is released to the atmosphere in 10 minutes. KCWA is unaware of any conceivable event that could actually cause such a catastrophic release at the facility. 7 "Alternate Release Scenario", which is a release that the PHA team concluded has a realistic (but small) chance of actually occurring at the facility. Worst-Case Release Scenario for Chlorine : Anhydrous liquid chlorine (chlorine gas that is stored as a liquid under pressure at ambient temperature) is imported to the site by truck and stored in a one-ton cylinder for use in the disinfection process. The Administrative Worst-Case Release Scenario assumes that the entire ton of chlorine is emitted as a gas cloud in 10 minutes, during a period of exceptionally calm winds and stagnant atmospheric conditions (1.5 meter/second wind speed and F stability) that would result in minimal dispersion of the gas cloud. The thermodynamic properties of anhydrous chlorine indicate that such a large instantaneous gas release is nearly impossible. The release of a large quantity of gaseous or liquid chlorine from a cylinder would result in rapid chilling of the chlorine, and the formation of liquid or frozen chlorine. The liquid or frozen chlorine would take much longer than 10 minutes to vaporize into a gas cloud. Nevertheless, the RMP rule dictates that the Administrative Worst-Case Scenario assumes the release of one-ton of gaseous chlorine. The formulas in EPA's RMP guidance for wastewater treatment plants were used to estimate the downwind impacts for the one-ton chlorine release. The formulas for chlorine apply to water treatment plants as well as wastewater treatment plants. Urban surface roughness conditions were used to account for buildings and trees in the vicinity of the facility. The model ind icated that the gas chlorine cloud would travel 1.3 miles before it dispersed to the 3 ppm Toxic Endpoint Concentration. The estimated residential population within a radius of 1.3 miles from the facility is 9,100 people. Alternate Release Scenario for Chlorine : The PHA team selected the following hypothetical accident as the Alternate Release Scenario: during cylinder change-out, an operator wearing protective gear accidentally ruptures the 3/8-inch pigtail pipe from the cylinder valve. Using EPA guidance, the calculated gaseous chlorine release rate is 21 pounds per minute (lb/min). This calculated release rate is conservative because according to the Handbook of Chlorination, for a one-ton cylinder at 68 0F, a chlorine withdrawal rate in excess of 0.28 lb/min (400 lb/day) will lead to a cooling of the system and potential freezing of the cylinder. Most of the released chlorine will freeze in a pool beneath the leak, and then be released at a much lower rate to the atmosphere. Ho wever, for the purpose of this evaluation, the calculated release rate of 21 lb/min was used. A repair kit (B-kit) is available, and the leak is repaired within 30 minutes. EPA suggested alternative release values of 3.0 m/s wind speed, and D stability were used. The EPA guidance formulas result in a distance of 0.1 miles to the endpoint of 3 ppm. The estimated residential population within a radius of 0.1 miles is 20 people. |