Res 2015-011/amendment No. 1 to the Service Contract for Wastewater Treatment Facilities Operations and Maintenance between the City and CH2M Hill

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(D) Aeration Basins. The volume of each aeration basin is approximately 0.926 million gallons at a sidewall depth of 16.2 feet. The design solids retention time ranges between 3.8 and 6.8 days, corresponding to a mixed liquor suspended solids concentration range of 1,500 to 3,000 mg /L. The bottoms of the basins are equipped with a fine - bubble air diffuser system that provide the required air rates up to 8,930 cubic feet per minute at standard conditions. The air to the diffusers is supplied by two 6,000 scfm capacity centrifugal blowers (including one standby) and one turbine blower. During normal operation, only one blower may be used. The effluent from the aeration basins is equally divided between the two final clarifiers. The clarifiers are 98 feet in diameter with a 12 foot side -water depth. Each clarifier is equipped with a spiral blade -style sludge collector that transports the sludge to a common point for return and waste. The sludge is periodically withdrawn from the clarifiers using the RAS and WAS pumps whose operation is controlled by timers. Both sets of pumps are located at the secondary sludge pumping station. RAS is returned to the head of the aeration basins by three (one stand -by) centrifugal pumps operating on a time - controlled basis, each rate at 3,300 GPM. The two (including one stand -by) WAS pumps have a capacity of 100 GPM each, and divert WAS to the primary clarifiers for co- settling with primary sludge. (E) Effluent Filters. The secondary effluent flows into the effluent filters for further suspended solids removal. There are three Infilco Degremont dual media filters, each 26.0 feet by 76.0 feet. The filters are designed to accommodate an average flow of 13.5 mgd and peak flow of 27 MGD. The filter loading rate is 2.6 GPM /sf and 5.2 GPM /sf at average and peak flows, respectively. Each filter unit is equipped with a backwash system mounted on a traveling bridge. The maximum backwash rate for the maximum flow is 25 GPM /sf. The backwash water is returned to the primary distribution box using three (including one stand -by) pumps, each at a capacity of 750 GPM. (F) Ultraviolet System. The disinfection of the filtered effluent is achieved through the UV system. Two UV channels measure 26.0 feet long and 4.75 feet wide, and have a sidewater depth of 2.0 feet. The UV lamps are located inside these channels. Each channel has four UV banks with 90 lamps each. The UV system is designed to treat an influent flow of 18.0 MGD with BOD5 and TSS concentrations of approximately 5 mg /L. The disinfected water flows from the UV system to the two re- aeration basins through two channels. Both re- aeration basins are equipped with fine bubble diffusers that are used to maintain the dissolved oxygen concentration above 6.0 mg /L. The air to the diffuser system is supplied by five (including one standby) blowers, rated at 415 scfm each. (G) Facilities Effluent. The Effluent from the Facilities is collected in a common box. A portion of the flow may be diverted to various customers for re -use (such as cooling water to a power plant customer), and the remaining flows by gravity through a 48 -inch outfall to the San Marcos River. (H) The components of the ATAD process are no longer in use. Tanks, pumps and valves remain intact.