Water Treatment Plant - Executive Summary |
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INTRODUCTION The Benbrook Water and Sewer Authority (BWSA) owns and operates a water treatment plant (WTP) located in Benbrook, Texas. The physical location of the WTP is in the southside of Benbrook at 1121 Shady River Court. The WTP treats raw water from Benbrook Lake and produces drinking water that is supplied to the residents of Benbrook. It has a current treatment capacity of 8.5 million gallons per day (MGD). Among the chemicals used in the treatment process, there is one chemical that is stored in quantities greater than the threshold level specified by the Environmental Protection Agency (EPA): chlorine. Chlorine is a disinfectant chemical used to destroy pathogenic organisms during the treatment process. It is stored at the WTP site as a gas that is liquified by pressure. The maximum amount of chlorine stored at the WTP site is 4,500 pounds. The BWSA policy regarding safety is to adhere to standard guidelines established for the water industry by equipment manufactur ers, chemical suppliers and professional organizations, and written standard operating procedures established specifically for the Benbrook WTP. BWSA coordinates appropriate aspects of its safety program with the City of Benbrook Fire Department. OFFSITE CONSEQUENCE ANALYSIS The offsite consequence analysis determined the offsite impact of a release of chlorine gas. Two different scenarios were considered regarding the release of chlorine gas from the WTP site: worst-case release and alternative release. The worst-case release scenario used the meteorological conditions specified by the EPA, a release of the largest chlorine gas container (150 pounds) in 10 minutes, and a standard modeling program called Breeze-Haz to determine the impact on the area surrounding the WTP site. The following EPA specified parameters were used in determining the impact of the worst-case release scenario: 1. Wind speed of 1.5 meters per second 2. Atmospheric stability class F 3. Urban topography The alternative release scenario used less severe meteorological conditions deemed appropriate for the BWSA plant site, a release of 33 pounds of chlorine gas in 3 minutes, and a standard modeling program called Areal Locations of Hazardous Atmospheres (ALOHA) to determine the impact on the area surrounding the WTP site. The following parameters were used in determining the impact of the alternative release scenario: 1. Wind speed of 3.0 meters per second 2. Atmospheric stability class D 3. Urban topography The offsite impacts of the worst-case and alternative release scenarios are summarized in the Offsite Consequence Analysis section of the report. FIVE YEAR ACCIDENT HISTORY During the past five years there have been no accidents involving the release of chlorine gas at the WTP. ACCIDENTAL RELEASE PREVENTION PROGRAM The operations and equipment at the WTP comply with several indu stry codes and standards regarding safety that are specific to the water industry. They include: American Society for Testing and Materials (ASTM) Standards, American Society of Mechanical Engineers (ASME) Standards, the Chlorine Manual of the Chlorine Institute, and the Texas Natural Resource Conservation Commission (TNRCC) Rules and Regulations for Public Water Systems. The Plant Operations and Maintenance (O&M) Manual includes the equipment manufacturer's instructions for operating and maintaining equipment used for the storage and application of chlorine gas. The O&M Manual also contains safety procedures concerning the handling of chlorine gas. Safety related equipment installed at the WTP include: 1. Automatic chlorine gas shutoffs. 2. Emergency vents for the failure of automatic shutoff valves. 3. Manual chlorine gas shutoffs. 4. Relief valves to prevent overpressurization of the chlorine gas system. 5. Chlorine gas detectors and alarms to detect gas leaks. The ongoing BWSA training program for its operations staff includes regular safety training sessions. Required TNRCC operator certification courses also include safety training. EMERGENCY RESPONSE PLAN The WTP emergency response for an accidental chlorine gas release is addressed by the plant's standard procedures and the City of Benbrook Emergency Management Plan. The WTP operations staff notifies the Benbrook Fire Department of any accidental release of chlorine gas that cannot be contained onsite. The Benbrook Fire Department, as described in the City's Emergency Management Plan, is the first responder to any toxic material emergency and will assume responsibility for the gas release from the WTP operations staff. |