CLIENT NAME - Sarasota.WaterAtlas.org

2.3.1.1.2 DegasificationRaw water enters one of four degasifiers in which countercurrent forced air and water flowover baffles to strip hydrogen sulfide from the water. The baffles are constructed ofhorizontally mounted PVC bars, which provide turbulence and surface area to aid indegasification. No significant bio-growth problems have been experienced, and an annualinspection of the interior has been sufficient for maintenance requirements.The flow from the degasifiers gravity feeds to a sand trap basin located directly below theequipment where sodium hypochlorite is drip injected to obtain a trace chlorine residualthroughout the remainder of the facility. Following the sand trap, the flow spills over a weirto the sedimentation basin to further remove fine sands and solids before entering thepressure filtration vessels.2.3.1.1.3 SedimentationFollowing degasification, water flows over a weir into the sedimentation basin. The basinwas designed to remove fine sands and solids prior to entering the pressure filtrationvessels. Residuals accumulate very slowly in the basin. When necessary, the solids arepumped to the backwash holding tank. The rectangular basin has grout-filled corners thatslope to form a circular bottom. The basin originally contained a residuals removal device;however, the scraper mechanism was not needed so facility staff removed it. A bypass linewas constructed around the sedimentation basin; however, it was designed to transfer onlyhalf of the facility’s design flow.2.3.1.1.4 Pressure FiltrationThe Carlton WTF utilizes five pressure filtration vessels for removal of fine particles notremoved by the sedimentation basin. The dual media filters are currently controlled byAllen-Bradley PLCs that are scheduled to be replaced due to their age and condition.Although the PLCs feed information into the facility’s SCADA system, facility staff controlthe filters manually.The pressure filtration tanks and downstream treatment processes (through the chlorinecontact tanks) are fed via 6 high-pressure feed water pumps. The pumps are located at thesedimentation basin effluent and are controlled with variable frequency drives (VFDs) inorder to maintain a constant pressure throughout the facility. The feed water pumps arerebuilt on a rotational basis (approximately every 5 to 6 years according to facility staff).The pressure filters are backwashed primarily based on a filter runtime of 200 hours. If thepressure in the filters exceeds 10 pounds per square inch (psi) prior to the 200-hour point,the filters go into an alarm mode and cannot be reset without performing a backwash cycle.However, facility staff could not recall a time when this occurred. The filters also enter anFINAL - August 31, 2005 14H:\Client\SAR Co_SAR\6873C00 WATER SUPPLY MASTER PLAN UPDATE\Deliverables\TM 2 - Water System Assets\Final\TM2 Final.doc