VWD Vallecitos IV Flow Control Facility - Executive Summary |
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Facility Description: The Vallecitos Water District (VWD) Vallecitos IV Flow Control Facility is located at 3690 North Twin Oaks Valley Road, San Marcos, California. Chlorine is used at the station to disinfect water intended for distribution to the domestic water supply system. The station is unmanned. A leak monitoring device will notify VWD personnel in the event of a chlorine leak. Chemicals Subject to EPA'S Accidental Release Prevention Program: VWD uses and stores chlorine in quantities large enough to trigger the Accidental Release Prevention Program: Typically, two 1-ton chlorine cylinders are in use, and four 1-ton cylinders are stored at the station. Chlorine is imported to the pump station via truck, stored onsite in a one-ton container, and used for disinfection operations. Accidental Releases During Past Five Years: The Vallecitos IV Flow Control Facility has not had any releases during the past five years that resulted in any injuries, off-site evacuations, or prop erty damage. Process Safety Management Accident Prevention Program: The Vallecitos IV Flow Control Facility is subject to OSHA's Process Safety Management (PSM) regulations for all equipment and operations associated with its chlorine system. VWD's PSM programs include the following to minimize the potential for an accidental release: 7 Review of the design of all equipment and controls for the chlorine system 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 VWD provides for its own employees. 7 Regular inspection of all equipment, monitoring systems and controls, including documentation of all inspections. 7 Prompt corrective action for any non-co nforming items identified by the regular inspections. 7 Safety reviews conducted prior to system startup, if any equipment or operations are modified. 7 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 work on the RMP-regulated system. 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/RMP program, and are actively consulted regarding safety issues. 7 Independent audits of the entire PSM/RMP program every three years. Emergency Response Procedures: VWD uses its First Response Chlorine Procedure Guide to provide step-by-step procedures for emergency response in the unlikely event of an accidental release. The key elements of the emergency preparedness program are as follows: 7 All plant staff (including administrative and clerical staff) are train ed in the specific elements of the program. 7 A team of engineers, supervisors and operators are trained, certified and equipped for hazardous materials (Hazmat) emergency operations to repair accidental releases. 7 In the event of a large release the facility would immediately contact a telephone call-down list that includes the San Marcos Fire Department, the San Diego County LEPC, and several nearby commercial establishments that could be affected if the wind was blowing toward them during the release. VWD's Recent Steps to Improve Safety: Current plans call for the station to be taken out of operation in August 1999. If chlorine is no longer used and/or stored at the station, then additional chlorine safety improvements will not be necessary. However, if the station remains in operation, VWD is considering the following actions to either reduce the likelihood or severity of potential chlorine releases. These suggestions are based on recent safety reviews conducted as part of the RMP evaluations. 7 Amend chlorine supplier's contract to state that the supplier is responsible and must take back any unsafe chlorine container, regardless of how long it has been at the facility. 7 Modify safety plans to include specific information to educate operators about the potential hazard resulting from failure of the vacuum regulator valve. 7 Modify chlorine inspection procedures to include quarterly replacement of polypropylene tubing. 7 Install a visual concentration indicator on the control panel in the main building to alert operators of chlorine levels in the building. 7 Revise the evacuation plan to consider wind patterns. 7 Protect the chlorine system from vandalism. 7 Install a permanent anchoring system (tie downs) for stored chlorine cylinders. 7 Install scrubber system to treat chlorine leaks. Hypothetical Accidental Release Scenarios: The Risk Management Plan must assess the downwind impacts of hypothetical accidental releases. EPA requires facili ties 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 ppm. VWD conducted safety reviews with plant operators, engineers and safety managers to evaluate a wide range of hypothetical accidents that could cause releases of chlorine. 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. VWD is unaware of any conceivable event that could actually cause such a catastrophic release at the facility. 7 "Altern ate Release Scenarios", which are releases that the safety review teams concluded have a realistic (but small) chance of actually occurring at the pump station. These hypothetical releases generally consist of valve leaks, temporary process upsets, and breakage to pipes or containers. 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 1-ton container for use in the disinfecting process. The Administrative Worst-Case Release Scenario assumes that the entire 1 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 as it blew downwind. The thermodynamic properties of anhydrous chlorine indicate that such a large instantaneous gas release is probably impossib le. If the entire 1 ton of liquid chlorine were somehow discharged from the tank it would spill onto the ground and immediately cool itself until it formed a puddle of "chlorine ice", which would take much longer than 10 minutes to evaporate into a gas cloud. Nevertheless, the RMP rule dictates that the Worst-Case Scenario assumes the release of 1 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. Rural surface roughness conditions were used to account for the vicinity of the facility. The model indicated that the gas chlorine cloud would travel 3.0 miles before it dispersed to the 3 ppm Toxic Endpoint Concentration. The estimated residential population within a radius of 3.0 miles from the facility is 15,000 people. Alternate Release Scenario for Chlorine : The follow ing hypothetical accident was selected as the Alternate Release Scenario: The pipe on the pressure side of the vacuum regulator fails, resulting in the release of chlorine through a 3/4-inch hole. The release is either observed or detected by the chlorine leak sensor. A repair kit (B-kit) is available, and the leak is repaired within 20 minutes. The release is partially contained by the building resulting in a reduction to 55 percent of the calculated unconfined release rate. Using EPA guidance, the calculated gaseous chlorine release rate is 46 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. However, for the purpose of this eval uation, the calculated release rate of 46 lb/min was used. The formula in EPA's RMP guidance for wastewater treatment plants were used to estimate the downwind impacts for the alternative release scenario. Rural surface roughness conditions were used. The model indicated that the gas chlorine could could travel 0.3 miles before it dispersed to the 3 ppm concentration limit. The estimated residential population within a radius of 0.3 miles from the facility is 50 people. |