West Alexander WWTP - Executive Summary
Greenwood Metropolitan District West Alexander WWTP |
1. Accidental release prevention and emergency response policies:
The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant accidental release prevention policy involves a unified approach that integrates technologies, procedures, and management practices. Accidental release prevention is a function of the safety devices (technology) inherent in the facility design, safe material handling practices used (procedures), and commitment to training of plant employees (management practices). All applicable requirements of the U.S. Environmental Protection Agency (EPA) Risk Management Prevention Program (40 CFR 68.65-87) are adhered to. It is a goal of the Greenwood Metropolitan District West Alexander Wastewater Treatment Plant to ensure plant and community safety through an aggressive program of hazard analysis, preventive maintenance, equipment testing, standard operating procedures, and employee training.
reenwood Metropolitan District West Alexander Wastewater Treatment Plant emergency response policy involves the preparation of a emergency preparedness plan which is tailored to the facility and to the emergency response services available in the community. The emergency preparedness program includes procedures for notification of the City of Greenwood and Greenwood County HAZMAT Teams (off-site mutual aid response), Greenwood County LEPC (community response plan), and SCDHEC (state response plan). The Greenwood Metropolitan District Wastewater Treatment Plant emergency preparedness program is based upon recommendations of the Water Environment Federation (WEF), the Chlorine Institute and is in compliance with the EPA Risk Management Emergency Response Program (40 CFR 68.90) requirements.
2. Stationary source and regulated substances handled:
The regulated substances handled and used at the Greenwood Metropolitan District West Alexander Wastewater Treatment Plant is chlorine. Th
e maximum intended inventory of chlorine at the facility at anytime is 4,000 pounds (2 ton containers).
The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant provides biological treatment for sanitary wastewater generated through out the Greenwood Metropolitan District service area. Chlorine is used in the wastewater treatment process to destroy nuisance and pathogenic microorganisms present in the wastewater (i.e., chlorine use as a wastewater disinfectant is an industry standard). The chlorination process includes chlorine container handling and storage facilities, chlorine feed system (piping, vacuum chlorinators, and injectors), and related safety equipment and instrumentation. The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant is manned 24-hours a day and access to the plant site is restricted to authorized personnel.
3. Worst-case release scenario and the alternative release scenarios:
The worst-case release scenario is d
efined by EPA as the release of the maximum quantity of a regulated substance from a process vessel or pipe line failure that will result in the greatest distance to the designated endpoint. The probability of the release occurring is not considered, it is just assumed to happen. A Program 3 regulated source must perform one worst-case release scenario analysis that is representative of all regulated toxic compounds that are present at the plant site above their designated threshold quantities. The worst-case release scenario at the Greenwood Metropolitan District West Alexander Wastewater Treatment Plant involves a catastrophic failure of a one ton chlorine container and the release of 2,000 pounds of chlorine to the atmosphere. The offsite consequence analysis for this scenario was performed following conditions pre-defined by EPA, namely release of the entire amount of chlorine as gas in 10 minutes, sulfur dioxide toxic endpoint of 0.0087 mg/l (i.e., the maximum airborne concent
ration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individuals ability to take protective action), and worst-case weather conditions (i.e., stable atmospheric conditions and a wind speed of 1.5 m/s). Also, no administrative or passive mitigation systems were considered in this scenario. The DEGADIS+ computer model was used to perform this consequence analysis. The results of the consequence analysis performed for the hypothetical worst-case chlorine release scenario did predict an offsite impact.
EPA describes the alternative release scenario as simply a more realistic release than the worst-case release or a release that is more likely to occur than the worst-case release. A Program 3 regulated source must perform an alternative release scenario analysis for each toxic compound that is present at the plant site above its
designated threshold quantity. The alternative chlorine release scenario chosen for the Greenwood Metropolitan District West Alexander Wastewater Treatment Plant involves the complete failure of the container mounted vacuum regulator resulting in the predicted release of 1,520 pounds of chlorine to the atmosphere over a two hour period. The alternative release scenarios chosen for the Greenwood Metropolitan District West Alexander Wastewater Treatment Plant were selected based on the results of a qualitative risk analysis of possible release alternatives. The offsite consequence analysis for this scenario incorporated less stable weather conditions (i.e., Stability D and wind speed of 3.0 m/s) and active mitigation (i.e., actuation of leak detector and emergency response by offsite mutual aid responders to control the leak). The DEGADIS+ computer model was used to perform the consequence analysis. The results of the consequence analysis performed for the hypothetical alternative
chlorine release scenario did predict an offsite impact.
While EPA requires analysis of the consequence of a worst-case release scenario, worst-case scenarios as defined by the EPA have an extremely low probability of occurrence. The worst-case release could only happen if the majority of the safety and technology features in use failed at the same time. Additionally, it would have to occur at exactly the time the worst-case weather conditions also existed, a most improbable event. Further, certain mandated consequence conditions such as the entire amount of chlorine or sulfur dioxide will be released as a gas in ten minutes and comparison of a ten minute release to a toxic endpoint based on a one-hour exposure value are unrealistic. However, there is no allowance in the EPA Risk Management Program (RMP) rule for making an adjustment to the worst-case release scenario conditions. For this reason, the alternative release scenarios should be the focus of prevention and preparedne
4. General accidental release program and the chemical-specific prevention steps:
The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant complies with EPA's RMP rule, OSHA's Process Safety Management standard (29 CFR 1910.119), and with all applicable state and local codes and regulations. The chlorination processes were constructed, and is operated, in accordance with recommendations of the WEF and Chlorine Institute. The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant accidental release prevention program is based on the following key elements:
High level of training for operators and maintenance personnel
Equipment inspection, testing, and preventive maintenance
Use of "industry standard" process and safety equipment
Use of accurate and effective operating procedures
Performance of hazard review of equipment and procedures
Implementation of an internal and external auditing program
Segregation of chem
ical processes for compatibility and fire prevention/control
Chlorine and sulfur dioxide leak detectors and alarm systems
Availability of SCBAs and chlorine and sulfur dioxide container leak repair kits
Approved parts inventory
5. Five-year accident history:
The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant has had an excellent record of preventing accidental releases over the past five years. Due to the effectiveness of the release prevention program, there have been no accidental releases of chlorine during the past five years.
6. Emergency Response Program:
The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant has an emergency preparedness plan that is integrated with the LEPC plan. The Greenwood Metropolitan District West Alexander Wastewater Treatment Plant maintains a mutual aid agreement with the City of Greenwood and Greenwood County HAZMAT Teams to provide emergency response services in the event of a chlorine
release. The plant emergency preparedness plan includes procedures for the notification of offsite mutual aid responders, LEPC, SCDHEC, and the public along with a discussion of actions to be taken in the event of a chlorine or sulfur dioxide release. The plan also addresses first aid and medical treatment.
7. Planned changes to improve safety:
The last Process Hazard Analysis (PHA) update was performed in May, 1999 and it resulted in no recommended process or operational changes. A PSM compliance audit was conducted in May 1999 and it resulted in a recommendation for minor changes (clarification) to the written SOPs and emergency preparedness plan. No other changes have been recommended.