Lake Granbury Surface Water and Treatment System - Executive Summary |
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Brazos River Authority Lake Granbury Surface Water and Treatment System The Lake Granbury Surface Water and Treatment (SWATS) plant is a regional water treatment and delivery system that can treat up to 5.04 million gallons per day of raw surface water. It then delivers the treated water through a 23-mile pipeline to wholesale water customers in Johnson County, Texas. SWATS uses conventional disinfection, clarification and filtration purification stages to treat the raw surface water. It also uses a state-of-the-art electrodialysis reversal process to remove excess salt from the lake water and render the water potable. Only chlorine and hydrochloric acid, used to disinfect the raw surface water, are stored above the allowable threshold quantity. SWATS received EPA Region VI's Regional Administrator's Environmental Excellence Awards for 1993 and 1996; the Texas Natural Resource Conservation Commission's Outstanding Performance Award for 1992-1996; and was voted The B est Tasting Water in 1996. Chlorine The chlorine is stored on south side of the chemical building in four one-ton cylinders, where it is used in groups of two. One group is used and the other is held as backup. When the first group is exhausted the backup group is engaged by an automatic switchover module. Three separate chlorine feeders are provided in the Chlorine Feed Room in the Chemical Building. The first feeder is dedicated to primary disinfection of the raw water as it enters the plant, the second to the secondary Feed disinfection of the finish water system, and the third to the supplemental disinfection of the finish water prior to transmission to Johnson County. The three systems are interconnected to allow the substitution of any one of the feeders for the other, but principally to allow standby of the secondary disinfection of the finish water and the supplemental disinfection of the transmission system. Chlorine is conveyed by vacuum through the chlorine fe eders to the injectors where solution water is added. The chlorine feed rates to each point of application are set proportional to flow rates measured by the raw water meter, blend and product water meter, and high service meter. The injector mixes the chlorine with water to pass the chlorine to other areas. The injectors send the chlorine and water solution into the finish water storage tank. Hydrochloric Acid The hydrochloric acid (HCl) is used in the plant as part of the Electrodialysis Reversal (EDR) process. The EDR process uses electric current to collect positive and negatively charged particles to further clarify the water. Minerals and other particles can build up and cause a hot spot or pressure loss down to a predetermined level. When this occurs operators run the acid cleaning task called clean-in-place (CIP). The CIP task requires a dilute hydrochloric acid solution to be pumped into the membrane stacks, recirculated and purged from the system to remove depo sition of the minerals causing the pressure loss or the hot spot. The HCl (34% solution) is stored in a 6,000 gallon tank in a side room next to the EDR building. It is administratively limited to a maximum quantity of 5,000 gallons (49,600 pounds). A chemical transfer pump moves the HCl to a smaller 1,800 gallon tank where it is mixed with water to bring about the weak HCl solution. Then a CIP pump transfers the solution through pipes to the EDR units. When the HCl solution is in the EDR unit it dissolves the build up and is transferred back to the 1,800 gallon storage tank for disposal. Accidental Release Prevention and Emergency Response Policies Authority policy requires a written emergency action plan, annual exercises and reviews of the plan, emergency response training for facility personnel, and coordination with local responders. In addition, smei-annual safety inspections are conducted by the Authority's Safety Officer and risk management consultants from our in surance company. Worst-Case Release Scenario The worst-case scenario is the release of 2,000 pounds of Chlorine (one-ton cylinder) in 10 minutes. The release rate is 200 lbs/min. The EPA rules specify an atmospheric stability of F and a wind speed of 1.5 meters per second. The maximum temperature in the last three years was 107 degrees F. No passive mitigation measures are in place. Therefore, the distance to the end point for chlorine vapor is 3.0 miles in a Rural environment. Alternative Release Scenario The plant did not have any reportable accidental releases of regulated chemicals in the past five years so we chose to analyze a broken 5/16" valve/pipe connection at the vessel interface for Chlorine. A vapor release was chosen because the plant does not use liquid chlorine. EPA's RMP Guidance for Waste Water Treatment Plants Reference Tables specify an atmospheric stability of D and a wind speed of 3 meters per second. According to Exhibit 4-15 (Chlorine Vapor), the release rate is 15 lbs/min. No passive or active mitigation measures are in place. Therefore, the distance to the end point for chlorine vapor is 0.2 miles in a Rural environment. Accidental Release Prevention Program All SWATS personnel receive awareness training to recognize and properly respond to accidental releases of hazardous chemicals. Plant supervisors employ "management by walking around" techniques to periodically observe the employees under actual operating conditions to ensure they follow proper procedures. Safety training is conducted throughout the year and safety inspections by outside agencies are conducted semi-annually. In addition, various state and local agencies conduct inspections of the facility. The chlorine process has two alarm systems. One alarm is a leak detector inside the Chlorinator Room where the chemical is dispensed to the required locations within the process. The second alarm is a chlorine switchover alarm colocated with the chlor ine tanks. This alarm indicates empty tanks. The hydrochloric acid tank, valves, pumps and pipiing are routinely inspected for corrosion and leaks. The tank is located within a diked area large enough to contain the total volume. If necessary, a drain will direct the chemical through underground pipes to holding lagoons safely away from any populated areas. Five-Year Accident History SWATs has not had any accidental releases of regulated chemicals in the last five years. Emergency Response Program SWATS has the capability to respond to and mitigate the release of on-site hazardous chemicals that present a moderate health and/or safety threat to SWATS and responding personnel, present a moderate potential for adverse environmental impact, are of limited size, and have low fire/explosion potential. If the spill/release is beyond the capability of on-site personnel, the City of Granbury's and Hood County's HAZMAT teams will respond by calling 911. Training and exercise s are conducted periodically. Planned Changes to Improve Safety We are adding 30-minute SCBA tanks to the current 15 minute tanks and will install a wind sock to help determine on-site wind conditions in the event of an accidental release. |