Temple-Belton Regional Sewerage System - Executive Summary
Brazos River Authority |
Temple-Belton Regional Sewerage System
The Temple-Belton Regional Sewerage System is an innovative and cost-effective regional sewerage system that serves the wastewater treatment needs of the urban areas in and around the cities of Temple and Belton, Texas. The plant was opened in 1975 and expanded in 1989. It has a system capacity of 10.0 million gallons per day permitted average flow; and 30.0 million gallons per day permitted peak flow. It currently treats an average daily flow of 5.2 million gallons per day. Plant awards include: two Environmental Excellence awards in 1994 from EPA Region VI; the Operations and Maintenance Excellence Award in 1992 from EPA Region VI; the Operations and Maintenance Excellence Award in 1992 from the Texas Water Commission; and 1st place in the 1992 Operations Challenge and 2nd place in the 1991Operations Challenge from the TWPCA/TWUA.
Only chlorine and sulfur dioxide, used to disinfect the water, are stored
above the allowable threshold quantity.
Chlorine serves to destroy disease-causing organisms and for prevention of algae growth in the Treatment Plant effluent. It is essential that all plant effluent have a chlorine residual of at least 1.0 mg/l after 20 minutes contact. The recommended dose for application to effluent from the activated sludge process is eight mg/l.
The chlorine is stored in 11 one-ton cylinders, and is used in groups of two and one. One group is in use and the other is held as backup. The second group is engaged by an automatic switchover module when the first group is exhausted. Each group is connected to a header that is provided with a separate vacuum regulator, which reduces the gas from a varying supply pressure to a constantly regulated vacuum. Chlorine gas feeder cabinets are wall-mounted in the Chlorination Room. One feeder is equipped with an automatic rate control valve. The other feeders are equipped with a manual rate control val
ve located on and adjusted from the front of the cabinet. Sufficient valving has been provided to allow different feeders to serve different junction boxes.
Induction units provide the vacuum required to pull the chlorine gas to the various points of application. These induction units create a vacuum through a motor-driven open propeller, located 24 inches below the minimum water surface, which also provides mixing of the chlorine gas with the wastewater and feeds directly into the Chlorine Contact Chambers. Chlorine feed rates are adjusted by the automatic rotameters in response to changes in the flow rate and residual. There are three chlorine contact chambers at the Temple-Belton Plant. Chlorine Contact Chambers No. 1 and No. 2 will each detain a flow of seven million gallons per day (mgd) for 20 minutes. Chlorine Contact Chamber No. 3 will detain a flow of 23 mgd for 20 minutes.
The concentration of the chlorine residual measured at the effluent weirs of th
e Chlorine Contact Chambers is used to determine the amount of sulfur dioxide dosed at the Effluent Structure. The plant effluent flow is to be dechlorinated to less than 0.1 mg/l for discharge.
Sulfur dioxide is stored in 3 one-ton cylinders, also connected to separate headers that are mounted on anchored supports. Almost all of the equipment used for sulfur dioxide feeding and induction, with the exception of the rotameters and some materials of construction, is identical to the equipment used for chlorine induction.
Sulfur dioxide gas feeders, or manual rotameters, are wall-mounted. One rotameter is equipped with an automatic rate control valve. The other rotameters are equipped with a manual rate control valve. Two of these rotameters have been supplied, each capable of delivering the maximum recommended dose of sulfur dioxide. Sufficient valving has been provided so that either induction unit for this system may be fed through either rotameter.
Sulfonation (the process of
sulfur dioxide reduction of the chlorine residual) takes place almost instantly. For this reason, it is not necessary to provide a contact chamber for detention of the flow. Sulfur dioxide is introduced into the flow at the Effluent Structure.
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, semi-annual safety inspections are conducted by the Authority's Safety Officer and risk management consultants from our insurance company.
Worst-Case Release Scenario
The worst-case scenario is the release of 2,000 pounds of Sulfur Dioxide (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 104 degrees F.
No passive mitigation measures are in place. Therefore, the distance to the end point for sulfur dioxide vapor is 3.1 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 both Chlorine and Sulfur Dioxide. A vapor release was chosen because the plant does not use liquid chlorine or sulfur dioxide. EPA's RMP Guidance for Wastewater 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. The very same conditions apply to Sulfur Dioxide. According to Exhibit 4-19 (Sulfur Dioxide Vapor), the release rat
e is 7 lbs./min, so the distance to the end point for sulfur dioxide vapor is also 0.1 miles in a Rural environment.
Accidental Release Prevention Program
Plant personnel are trained to handle chemical containers in such a manner as to prevent leaks or spills while connecting or disconnecting containers. Personnel are also trained to shut down the system by closing the cylinder valve in the event of an emergency or anticipated emergency.
Five-Year Accident History
The plant has not had any accidental releases of regulated chemicals in the last five years.
Emergency Response Program
TBRSS 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 TBRSS 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 Bel
ton and Bell County's HAZMAT teams will respond by calling 911. Training and exercises are conducted periodically.
Planned Changes to Improve Safety
Installation of a new SCADA system will improve monitoring abilities for chemical spills and releases.