VWD Twin Oaks Reservoir - Executive Summary |
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Facility Description: The Vallecitos Water District (VWD) Twin Oaks Reservoir Facility is located at 3896 El Paso Alto Road, San Marcos, California. The facility is still being constructed and is scheduled to be operational by mid-February. The facility provides storage of potable water received from the Second San Diego Aqueduct operated by the San Diego County Water Authority. Chlorine will be used at the station to disinfect water intended for distribution to the domestic water supply system. The station will be unmanned and is equipped with chlorine release dection equipment, automated alarm and auto-dialing equipment, and a scrubber system. 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 will use and store chlorine in quantities large enough to trigger the Accidental Release Prevention Program: Typically, two 1-ton chlorine cylinders will be in use, and up to eight 1-ton cylinders can be stored at the station. Chlorine will be 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 previous Vallecitos IV Flow Control Facility that the new Twin Oaks Reservoir Facility will be replacing 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 Twin Oaks Reservoir 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-conforming 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 re garding 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 trained 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 chlorine 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 p lans call for the facility to be operational by early-February. Based on the available design and specification information the facility appears to provide adequate protection from accidental releases. The new facility will have a scrubber installed to handle a 2,350 pound chlorine release, a vacuum delivery system will minimze the amount of chlorine released downstream of the cylinder mounted regulator, and intrusion alarms will be installed to protect the site from vandalism. Two weeks of training will be provided by the Contractor to familiarize the VWD staff with the operation and maintenance of the new facility. Prior to start up of the facility, a copy of the operations and maintenance manual containing the chlorine handling safety procedures, material safety data sheets (MSDS), and the emergency response plan will be stored at the site for VWD personnel use. Hypothetical Accidental Release Scenarios: The Risk Management Plan must assess the downwind impacts of hypothe tical 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 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 ca tastrophic release at the facility. 7 "Alternate 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 impossible. 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 2.2 miles before it dispersed to the 3 ppm Toxic Endpoint Concentration. The estimated residential population within a radius of 2.2 miles from the facility is 7,500 people. Alternat e Release Scenario for Chlorine : The following 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. Using EPA guidance, the calculated gaseous chlorine release rate is 21lb/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 evaluation, the calculated release rate of 21 lb/min was used. An estimated 1,260 pounds of chlorine would be released into the storage room. The sealed building will contain the release and the scrubber system will be activated to treat and remove to chlorine gas. The capacity of the scrubber system is more than one-ton (2,350 pounds), so the system meets RMP requirements. The scrubber system is designed to treat the released chlorine to an acceptable concentration of no more than 5 ppm before discharge so that chlorine discharge levels to the offsite environment will be below the regulated 3 ppm Toxic Endpoint Concentration. The scrubber will prevent any offsite impact. |