Pinole-Hercules Water Pollution Control Plant - Executive Summary |
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Facility Description: The Pinole-Hercules Water Pollution Control Plant (WPCP) serves residential and commercial customers in the Pinole and Hercules communities located adjacent to San Pablo Bay in Contra Costa County, California. Residential areas are adjacent southeast of the WPCP. Downtown Pinole is located approximately one-half mile southeast of the WPCP. The WPCP is bordered by Southern Pacific Transportation Company railroad tracks to the south and east, and San Pablo Bay to the north and west. Description of Processes: The WPCP system primarily consists of two major processes: wastewater treatment and solids handling. The wastewater treatment process components include headworks, three primary clarifiers, grit removal, four aeration basins, four secondary clarifiers and a chlorine contact basin. The solids handling process components include primary and secondary sludge digesters and sludge thickener. The average daily WPCP flow rate is approximately 2.2 million gallons pe r day. The WPCP operates continuously. Under normal conditions, the WPCP is attended by Pinole-Hercules WPCP personnel seven days per week between 8:00 a.m. and 4:30 p.m. Two to four operators are present at the WPCP during the week days, and a minimum of two operators are present during the weekend. The WPCP is not attended outside of normal working hours. Chemicals Subject To EPA's Accidental Release Prevention Program: Chlorine and sulfur dioxide are the only acutely hazardous materials stored at the WPCP in quantities above State threshold quantities. The threshold quantity for chlorine is 100 pounds, and the threshold quantity for sulfur dioxide is 500 pounds. Liquefied chlorine is stored in 1-ton cylinders at a maximum quantity of 16,000 pounds (eight full cylinders). Liquefied sulfur dioxide is also stored in 1-ton cylinders at a maximum quantity of 8,000 pounds (four full cylinders). Full chlorine and sulfur dioxide cylinders are stored in a cylinder storage room in the Chlo rination Building. Accidental Releases During Past Five Years: Pinole-Hercules WPCP personnel reviewed incident investigation reports from June 1994 to June 1999 to identify accidental releases of chlorine or sulfur dioxide that resulted in deaths, injuries, significant property damage, evacuations, sheltering in place, or environmental damage onsite or offsite. No significant releases of chlorine or sulfur dioxide occurred during this period. Process Safety Management Accident Prevention Program: The Pinole-Hercules WPCP 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. The WPCP'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 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 dioxide 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/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: Emergency procedures are described in WPCP's Emergency Response Procedures. In the unlikely event of an accidental release of chlorine or sulfur dioxide, the key elements of WPCP's emergency response program are as follows: 7 Plant 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 an audible alarm system to alert the staff of a potential accident. 7 In the event of a large release, the Contra Costa County Health Services Department would immediately implement the Community Alert Network. The WPCP's Recent Steps to Improve Safety: The recommended changes to improve safety that resulted from the process hazard analysis of the risk management prevention program have been imple mented. The most significant safety improvement was the installation of a scrubber system to treat chlorine and sulfur dioxide releases. 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 both chlorine and sulfur dioxide is 3 ppm. The Pinole-Hercules WPCP conducted a process hazard analysis (PHA) during the California risk management and prevention program, which included an evaluation of potential chlorine and sulfur dioxide release scenarios. A review of the PHA incorporated th e safety improvements to the facility, and revised accidental release scenarios were considered. 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. 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 or sulfur dioxide (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 or sulfur dioxide is emitted as a gas cloud in 10 minutes, during a period of exceptionally calm win ds 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 or sulfur dioxide 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 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 EPA's RMP*Comp program was used to estimate the downwind impacts for the one-ton chlorine or sulfur dioxide release. Urban surface roughness conditions were used to account for buildings and trees in the vicinity of the facility. Passive partial containment by the storage room was taken into consideration. The model indicated that a gas chlorine cloud would travel 0.9 miles before it dispersed to the 3 ppm Toxic Endpoint Concentration. The model indicated that a sulfur dioxide cloud would also travel 0.9 miles before dispersing to its Toxic Endpoint Concentration (also 3 ppm). Using census data from the Marplot program, the estimated population within the worst-case scenario radius is 8,900 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 1/8-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 2 lb/min, and the gaseous sulfur d ioxide release rate is 1 lb/min. These calculated release rates are 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. A high sulfur dioxide release rate will result in a similar effect. An estimated 120 pounds of chlorine or an estimated 60 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. |