Change of Leadership - Water Environment Association of Texas

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6 | Texas WET May 2009WET Tech Talk Continued from page 5of 315 MGD during extended wet weather events. Thehydrograph shows that the volume under the curveabove flow 315 MGD is equivalent to the necessarytotal storage volume. The existing six equalizationbasins will be utilized for wet weather storage and totalapproximately 22 MG of storage capacity. As a result,approximately 78 MG of storage capacity is required inthe on-site storage basin. Figure 1 shows the hydrographfor the year 2020 design storm.The primary purpose of the on-site storage pumpstation is to drain the basin after a wet weather event. Itcan also serve as additional pumping capacity during dryweather emergencies. Figure 3 shows a schematic of thewet weather operation of the peak flow storage facilities.Figure 3: Peak Flow Storage Facilities Flow SchematicFigure 1: Year 2020 Design Storm Hydrographwith Required Storage Capacity OperationThe peak flow storage facilities will store peak flowsin excess of the plant’s existing biological treatmentcapacity, which will reduce the flows that the CRWStreatment plant would be required to treat and dischargeduring wet weather events, and would potentiallyeliminate the need to expand the treatment capacity tohandle projected peak wet weather flows.The peak flow storage facilities will include alarge 125-MG storage basin, an on-site storage pumpstation, fine screens, and a direct gravity connection tothe collection system. These facilities will provide thecapability to store screened raw wastewater, in additionto potential future high-rate clarification, chemicallyenhanced primary treatment effluent, or secondaryeffluent during dry weather or wet weather conditions. Apartition wall will divide the basin into an eastern sectionand a western section. Figure 2 shows a section of theproposed storage basin.Figure 2: Section of Proposed On-Site Storage BasinPeak flows will be screened, degritted, and conveyedto the basin. Future uses could include the use ofhigh-rate clarification or chemically enhanced primarytreatment process units for suspended solids removalprior to storage. Flows can be conveyed to temporarystorage in either the existing equalization basins or thewestern section of the storage basin. Gravity influentflows in excess of 405 MGD will be conveyed to theeastern section of the storage basin directly from oneof the main plant interceptors. The excess flows willundergo fine screening before storage.As the wet weather flows subside, the eastern sectionof the basin can be drained, pumped by the 50-MGDpump station to the plant headworks, equalizationbasins or directly to secondary treatment. Sluice gatesin the partition wall between the eastern and westernsections of the basin will be opened, allowing thewastewater stored in the western section to drain to thepump station. During smaller wet weather events, thepartitioned basin allows the use of one section. Duringlarger wet weather events, wastewater can be allowed tospill over the partition wall, filling the eastern section.The connection to interceptor also allows storageduring dry weather emergencies affecting the operationof the influent pump stations. Up to approximately 220MGD can be diverted to the east basin and the on-sitestorage pump station can pump from that location at arate of 50 MGD back to the plant headworks.DesignTRA has contracted the Design Team to provideengineering services for the design of the peak flowstorage facilities. The proposed storage basin willprovide the capability to temporarily store screened rawwastewater and/or secondary effluent during dry weatheror wet weather conditions. In addition future plansinvolve storage using high-rate clarifiers or potentiallychemically enhanced primary treatment effluent. The
May 2009 Texas WET | 7storage basin will be sized to accommodate up to 125MG of wet weather storage and approximately 51 MG ofstorage for dry weather emergencies. A partition wall willdivide the basin into an eastern section and a westernsection, which will provide the capability to separatehigher quality wastewater from raw wastewater insidethe basin. During normal operation the raw wastewaterin the east section will not mix with the primary effluentin the west section of the basin. Only during emergencystorage conditions there will be a mix of east and westbasin wastewater.A new junction box will be constructed at the maininterceptor feeding the plant. From the new junction box,approximately 2,300 linear feet of 110-inch piping will berouted through the plant to the proposed on-site storagepump station. The influent conveyance piping will allowinstantaneous flows of up to 220 MGD to flow by gravityto the on-site storage pump station.Flow from the interceptor would be routed through a200-MGD screening structure prior to discharge into theon-site storage basin. The on-site storage basin pumpstation will be a 50-MGD submersible pump wet wellpump station, consisting of three 25-MGD submersiblepumps equipped with variable frequency drives. Theon-site storage pump station will have the ability to serveas a dual-use pumping facility to allow for filling andemptying of the proposed on-site storage basin.The new storage basin is being designed to storea significant volume of wastewater. The existing 112-MG borrow pit is located within the slurry trench walland will provide the capacity and footprint requiredfor the new storage basin. The basin was designedwith a stepped-configuration, following the existingshale layer contour, to minimize the amount of shaleexcavation. The top length and width of the basin willbe approximately 1,100 feet and 700 feet, respectively.A partition wall will divide the two levels, allowingadditional operational flexibility. The eastern sectionof the basin will be designed to provide 51 MG gravitystorage of raw wastewater from the collection systemand the western section will be design to provide storageof approximately 26 MG of primary treated wastewaterto the top of the partition wall. The basin can be filledabove the partition wall for a maximum storage volumeof 125 MG. The eastern section of the basin will have abottom elevation of 368 feet and the western section at390 feet.The basin side slopes shall be at 3H:1V and the basinbottom shall slope from west to east at 0.25 percentwith a maximum water surface elevation at 410 feet. Thebasin bottom slab and the side walls shall be reinforcedconcrete with a minimum thickness of 8 inches. Eachsection of the basin shall also be provided with an accessramp for vehicle and maintenance equipment access.The partition wall shall be 24-inch thick reinforcedconcrete and will have sluice gates to drain the westernsection of the basin into the eastern section. A 5-footwide channel shall be constructed to the east of thepartition wall to evenly distribute flow from the westernsection across the width of the basin and flush theeastern section.The basin design includes an automatic flushingsystem that would rinse the basin walls and bottom toreduce the build-up of particles that may settle duringtemporary storage and to minimize plant staff’s effortin cleaning the basin. The flushing system would consistof two separate systems for the eastern basin section:a distribution system for rinsing the walls and a gate/weir system on the partition wall for flushing the basinbottom. Both systems would use the higher qualitywastewater stored in the western section to rinse thewalls and floor of the eastern section. As a secondarysystem for basin wall cleaning, a water cannon systemwill be installed as well.The flushing water distribution system will consistof a 48-inch header pipe installed in the basin wall,routed along the perimeter of the eastern section, withports spaced at 10-foot intervals along the walls. Watercannons will also be installed along the basin perimeterto provide additional flushing flexibility.Physical Hydraulic ModelingThe Design Team is collaborating with Dr. DaveWerth, with Clemson Engineering Hydraulics Inc., duringContinued on page 31
Page 1 and 2: Official Publication of the Water E
Page 3 and 4: May 2009 Texas WET | 3Leadership fo
Page 5: May 2009 Texas WET | 5WET Tech Talk
Page 9 and 10: The Key to OptimizingCloth Media Fi
Page 11 and 12: May 2009 Texas WET | 11be installed
Page 13 and 14: May 2009 Texas WET | 13planned to b
Page 15 and 16: March 2009 Texas WET | 15Student an
Page 18 and 19: 18 | Texas WET March 2009Highlights
Page 20 and 21: 2 0 | Texas WET May 2009Utility Man
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Page 24: 24 | Texas WET May 2009WEF and WEAT
Page 27 and 28: May 2009 Texas WET | 27WEAT Outstan
Page 29: May 2009 Texas WET | 29If you would
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Change of Leadership - Water Environment Association of Texas

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