Rio Vista Water Treatment Plant - Executive Summary |
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Facility Description: The Castaic Lake Water Agency (CLWA) Rio Vista Water Treatment Plant (RVWTP) is located at 27234 Bouquet Canyon Road in Santa Clarita, California. The Plant is on a property covering 65 acres. RVWTP is provided State Project water stored in Castaic Lake. The plant is capable of treating 30 million gallons of water per day. Raw water is first delivered to the pre-ozone contactor where ozone is applied for pre-oxidation and pre-disinfection. Ozonated water then enters the rapid mix structure where coagulants are added. The water is then fed to up-flow clarifiers, and then to a gravity filtration system. In the final stage, filtered water is disinfected with chlorine, monitored for chlorine residual, and released to CLWA's transmission system for distribution. Potentially hazardous chemicals that are stored and used onsite or for which storage is available include chlorine, hydrogen peroxide, diesel fuel, liquefied oxygen, and sodium hydroxide. Liquid chlorine, us ed for disinfection of water, is stored in one-ton cylinders. The maximum quantity of chlorine stored at the plant is 16 cylinders (32,000 pounds). Chlorine is present in quantities above the RMP threshold. The other chemicals are either not covered under the RMP program, or are present in quantities below the thresholds. Chemicals Subject To EPA's Accidental Release Prevention Program: CLWA Rio Vista Water Treatment Plant uses chlorine stored in quantities large enough to trigger the Accidental Release Prevention Program. Chlorine for use in disinfection operations is delivered to the plant by truck and stored onsite in one-ton cylinders. Accidental Releases During Past Five Years: The CLWA Rio Vista Water Treatment Plant 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 CLWA Rio Vista Water Treatment Plant is subject to OSHA's Process Safety Man agement (PSM) regulations for all equipment and operations associated with its chlorine system. The CLWA's PSM programs include the following activities 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 CLWA provides for its own employees. 7 Regular inspection of all equipment, monitoring systems and controls, with 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 o perations 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 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: CLWA Rio Vista Water Treatment Plant uses its Emergency Response Plan (ERP) to provide step-by-step procedures for emergency response in the unlikely event of an accidental release. The O&M Supervisor (Operations) maintains the ERP. The key elements of CLWA's emergency preparedness program are as follows: 7 The plant uses a combination of audible alarms and a plant loudspeaker system to alert the staff of a potential acc ident and to conduct in-plant communications. 7 In the event of a large release, the facility would immediately contact the Los Angeles Fire Department. 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 Concentrations for chlorine is 3 ppm. CLWA conducted safety reviews with plant operators, engineers and safety managers to evaluate a wide range of hypothetical accidents that could cause a release of chlorine. In accordance with EPA's rule, two general types of hypothetical accidental release sc enarios 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. 7 "Alternate Release Scenarios", which are releases that the safety review teams concluded have a realistic (but small) chance of actually occurring at the plant. These hypothetical releases generally consist of flange leaks, temporary process upsets, and breakage to pipes or tanks. Worst-Case Release Scenario for Chlorine : Anhydrous liquid chlorine (chlorine gas that is stored as a liquid under pressure at ambient temperature) is delivered 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 meters/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 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 indicated that the gas chlorine cloud would travel 1.3 miles before i t dispersed to the 3 ppm Toxic Endpoint Concentration. The estimated residential population within a radius of 1.3 miles from the facility is 4,700 people. Alternate Release Scenario for Chlorine : Because of improvements at the facility, the hypothetical accident identified by the Process Hazard Analysis (PHA) team was modified to the following Alternate Release Scenario: The pipe connecting an on-line cylinder and the header manifold within the high pressure system breaks. Chlorine is released through the opening. The leak occurs during daytime hours with two operators on duty. A leak detector in the chlorine storage room sets off an alarm that is heard by the operators. Within 20 minutes, the release is stopped. Using EPA guidance, the calculated gaseous chlorine release rate is 6 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 evaluation, the calculated release rate of 6 lb/min was used. The sealed building contains the release, and the scrubber system is activated. The amount of chlorine released to the room is 120 pounds. The capacity of the scrubber system is one-ton (2,000 pounds), so the capacity of the system is not exceeded. The system treats the chlorine to an acceptable concentration before discharge, so the chlorine discharge to the outside environment is less than the endpoint of 3 ppm. Dispersion modeling is not required because the release will not have an offsite consequence. |