RCWD Santa Rosa Water Reclamation Facility - Executive Summary
Facility Description: |
The Rancho California Water District (RCWD) Santa Rosa Water Reclamation Facility is located near the community of Temecula in Riverside County, California. The facility includes chlorine use for disinfection, and sulfur dioxide for removal of chlorine residual.
The chlorine system consists of the chlorine bulk storage system, chlorinators, chlorine rapid mix basins, and chlorine contact basins. Chlorine is stored onsite in eight, one-ton cylinders. During normal operations, chlorine is withdrawn from the cylinders and the gaseous chlorine is fed by chlorinators to injectors which mix chlorine with water, forming a solution.
The dechlorination system consists of sulfur dioxide storage and sulfonators. The sulfur dioxide storage consists of two identical banks of four one-ton cylinders located inside the chlorination/dechlorination building.
A scrubber system is available to treat releases of chlorine or sulfur dioxide.
Chemicals Subject To EPA's Accidental R
elease Prevention Program:
RCWD uses chlorine and sulfur dioxide at the Santa Rosa Water Reclamation Facility in quantities large enough to trigger the Accidental Release Prevention Program. The maximum quantities present are 28,000 pounds each of chlorine and 32,000 pounds of sulfur dioxide. Chlorine and sulfur dioxide are transported to the facility by truck, and stored onsite in one-ton cylinders.
Accidental Releases During Past Five Years:
The RCWD Santa Rosa Water Reclamation Facility has not had any releases of chlorine or sulfur dioxide during the past five years that resulted in any injuries, off-site evacuations, or property damage.
Process Safety Management Accident Prevention Program:
The RCWD Santa Rosa Water Reclamation Facility is subject to OSHA's Process Safety Management (PSM) regulations for all equipment and operations associated with chlorine storage and disinfection systems, and sulfur dioxide storage and dechlorination processes. RCWD'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 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 RCWD 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 or sulfur d
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/RMP program, and are actively consulted regarding safety issues.
7 Independent audits of the entire PSM/RMP program every three years.
Emergency Response Procedures:
Emergency procedures are described in RCWD's Emergency Response Plan. In the unlikely event of an accidental release of chlorine or sulfur dioxide, the key elements of RCWD's emergency response 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 a
udible alarms and a plant loudspeaker system to alert the staff of a potential accident 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 Riverside County Fire Department, and several nearby commercial establishments that could be affected if the wind were blowing toward them during the release.
RCWD's Recent Steps to Improve Safety:
Based on recent safety reviews that were conducted as part of the RMP evaluations, RCWD is considering the following actions to either reduce the likelihood or severity of potential chemical releases:
7 Modify the chemical handling/delivery SOP to include specific inspection guidelines and an inspection record that can be kept at the facility.
7 Modify safety plan to include specific information to educate operators about the potential hazard resulting from failure of the vacuum control/regulator valve.
Hypothetical Accidental Release Scenario
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 ppm.
VWD 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. VWD is unaware of any conceivable event that could actuall
y 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 and Sulfur Dioxide:
Anhydrous liquid chlorine and sulfur dioxide (gases that are stored as liquids under pressure at ambient temperature) are imported to the site by truck and stored in a one-ton cylinder for use in the chlorination/dechlorination process. The Administrative Worst-Case Release Scenario assumes that the entire ton of chlorine or sulfur dioxide 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 and sulfur dioxide indicate that such a large instantaneous gas release is nearly impossible. The release of a
large quantity of gaseous or liquid chlorine or sulfur dioxide from a cylinder would result in rapid chilling of the chlorine or sulfur dioxide, and the formation of liquid or frozen chlorine or sulfur dioxide. The liquid or frozen chlorine or sulfur dioxide 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 or sulfur dioxide.
The formulas in EPA's RMP guidance for wastewater treatment plants were used to estimate the downwind impacts for the one-ton chlorine or sulfur dioxide release. The formulas for chlorine and sulfur dioxide 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 a gas chlorine cloud would travel 1.3 miles before it dispersed to the 3 ppm Toxic Endpoint Concentration. The model a
lso indicated that a sulfur dioxide cloud would travel 1.3 miles before dispersing to its Toxic Endpoint Concentration (also 3 ppm).
Figure 1 shows the calculated distance to the chlorine or sulfur dioxide endpoint for the worst case scenario. The estimated residential population within a radius of 1.3 miles from the facility is 2,000 people.
Alternate Release Scenario for Chlorine and Sulfur Dioxide :
The following hypothetical accident was selected as the Alternate Release Scenario: the valve on the pressure side of the vacuum regulator fails, resulting in the release of chlorine or sulfur dioxide through a 3/8-inch hole. The release is either observed or detected by the leak sensors. A repair kit (B-kit) is available, and the leak is repaired within 60 minutes.
Using EPA guidance, the calculated gaseous chlorine release rate is 21 lb/min, and the gaseous sulfur dioxide release rate is 10 lb/min. These calculated release rates are conservative because according to the Handbook o
f 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. A high sulfur dioxide release rate will result in a similar effect. An estimated 1,260 pounds of chlorine or an estimated 600 pounds of sulfur dioxide will be released into the storage room.
The sealed building contains the release, and the scrubber system is activated. The capacity of the scrubber system is two-tons (4,000 pounds), so the capacity of the system is not exceeded. The system treats the chlorine or sulfur dioxide to an acceptable concentration before discharge, so the chlorine or sulfur dioxide discharge to the offsite environment is less than the toxic endpoints, and there is no impact.