Nevada City Wastewater Treatment Plant - Executive Summary |
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The City of Nevada City has instituted a Risk Management Program for their wastewater treatment facility, Nevada City Wastewater Treatment Plant, as required by Federal Accidental Release Prevention (ARP) Program regulations at 40 CFR Part 68. The Risk Management Program identifies the equipment, procedures, maintenance, inspection, and training associated with Regulated Substances (RS's) handled at this facility in excess of Federal threshold quantities; describes the structured assessment of hazards which was conducted to assess possible effects on employees and offsite public and environmental receptors; provides the results of an offsite consequences analysis; defines a prevention program, emergency response program, and mitigation measures to reduce the probability and magnitude of accidental releases of RS's; and establishes a schedule and responsibilities for implementation of mitigation measures and auditing of program elements. This Risk Management Plan (RMP) is being filed as required by ARP regulations in order to report the elements of the current Risk Management Program and to describe further measures planned to mitigate or prevent accidental releases of RS's. STATIONARY SOURCE AND REGULATED SUBSTANCES HANDLED The City of Nevada City's Wastewater Treatment Plant is located at 650 Jordan St., Nevada City, CA in Nevada County, and uses chlorine and sulfur dioxide for disinfection and dechlorination in quantities greater than the Federal threshold quantity for these RS's. The facility is located in a ravine at the edge of town. There are 3 full-time employees at this site. Chlorine and sulfur dioxide are received in ton containers by truck, handled with an electric hoist, and stored on ton container scales inside the building. The chlorine is used for odor control of the influent wastewater, to disinfect the wastewater effluent, and for other process uses. The sulfur dioxide is used to dechlorinate the disinfected effluent for aquatic toxicity control. Pressurized gas within a ton container is reduced to vacuum at a vacuum regulator valve mounted directly onto the ton container's gas valve. From there, the gas under vacuum is metered through rate valves and rotameters in chlorinators or sulfonators located in a separate room, and drawn into water solution by the passage of pressurized water through an injector. ACCIDENTAL RELEASE PREVENTION AND EMERGENCY RESPONSE POLICIES It is the policy of the City of Nevada City that the receipt, storage and handling of chlorine and sulfur dioxide at its facility be done in a manner which meets regulatory requirements and minimizes the probability and severity of accidental releases of chlorine or sulfur dioxide to the atmosphere, in order to protect the health and safety of its workers, the public, and the environment. In order to accomplish this goal, the City of Nevada City has gathered safety information on chlorine and sulfur dioxide and on the process, equipment and procedure s involving chlorine and sulfur dioxide; performed a structured assessment of hazards of the process and external events which might affect the process; performed an offsite consequences analysis of defined release scenarios; established a written program for prevention and mitigation of accidental releases; and established a written emergency response program coordinated with emergency response agencies. WORST CASE RELEASE SCENARIO A single "worst case" release scenario is required to be considered for each stationary source, resulting in the maximum distance to an endpoint for all toxic RS's contained on site above the threshold quantity. The worst case release scenario for toxic chemicals is defined in the ARP regulations as the release of the contents of the largest single container of RS (in this case chlorine) over a period of 10 minutes. The scenario considered the release of the contents of the largest container of chlorine on site, in this case 2,000 lb. This release scenar io is not physically possible, due to the characteristics of chlorine. ALTERNATIVE CASE RELEASE SCENARIO An "alternative case" release scenario is required to be considered for each toxic RS handled in quantities greater than the threshold quantity at the site. The "alternative case" scenario is described in the ARP regulations as a likely release resulting in offsite effects, considering administrative controls and mitigation measures in place, and is to be determined by the facility operators as part of the Process Hazard Analysis required to be performed during RMP development. The "alternative cases" considered for this facility are the release of chlorine or sulfur dioxide gas from a ton container due to operator error during hookup, with the release secured by properly trained and equipped responders closing the gas valve after 30 minutes. ADMINISTRATIVE CONTROLS Administrative controls in effect at the City of Nevada City which were considered to mitigate the severity of th e Worst Case and Alternative Case release scenarios include the City of Nevada City's written policies and procedures for training of operators and maintenance personnel, written procedures for control of the inventory of chlorine and sulfur dioxide at the facility, and policies regarding quality level of replacement materials and components for the chlorine and sulfur dioxide system. MITIGATION MEASURES No mitigation measures were considered to limit the severity of the Worst Case scenario. No passive mitigation measures were considered to limit the severity of the Alternative Case scenario. Active mitigation was considered for the Alternative Case, in the form of response of trained personnel in a timely manner following established written emergency response procedures. GENERAL ACCIDENTAL RELEASE PREVENTION PROGRAMS General accidental release prevention programs instituted by the City of Nevada City are categorized as administrative (management) programs; procedures, training, and engineering controls; and emergency response programs. The City of Nevada City has instituted a Process Safety Management (PSM) Program meeting OSHA requirements at 29 CFR 1910.119 covering its disinfection and dechlorination process. This constitutes the general accidental release prevention program for the City of Nevada City's operations. The program and document mangement procedures included in the PSM Program will be used as the management system for the Risk Management Program. CHEMICAL-SPECIFIC RELEASE PREVENTION STEPS Release prevention steps specific to chlorine and sulfur dioxide have been identified and implemented. These include, among other things, creation of numerous facility-specific operation procedures with check boxes for completion of critical steps. FIVE YEAR ACCIDENT HISTORY There have been no accidents involving chlorine or sulfur dioxide at this facility within the past five years resulting in injuries or offsite consequences. EMERGENCY RESPONSE PRO GRAM The City of Nevada City's Emergency Response Program applicable to chlorine and sulfur dioxide has been coordinated with Nevada County Department of Environmental Health, the local agency responsible for hazardous materials inventory reporting and release response coordination. The City of Nevada City maintains First Responder capability within its own staff, and has arranged with the City of Nevada City Fire Department to assist in providing Incident Command support. PLANNED CHANGES TO IMPROVE SAFETY All of the improvements and mitigation measures identified in the process hazard analysis which the City of Nevada City committed to accomplish have been completed or are in progress. Any other measures identified by employees during workplace hazard surveys, or as a result of audit activities, will be thoroughly reviewed and considered for implementation. |