Professional Services Agreement - Arcadis US Inc - Secondary Treatment and Disinfection Improvements at WWTP

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by a separate drain pump that has exceeded its useful life. It is assumed that their associated return sludge pumps will be able to drain the clarifier with the new mechanisms; this will be evaluated and confirmed. Skimmings removal is provided in all clarifiers. As part of this project, the internal clarifier equipment including the sludge collector mechanisms and scum removal will be replaced and effluent weirs will be rehabilitated. For Final Clarifier Nos. 1 through 3 the effluent troughs will also be replaced. The existing scum removal beyond that being replaced internal to the clarifiers will be reused. In addition, the clarifier structures will be inspected and rehabilitated and repaired, as necessary. This also includes the pressure reducing valves within the tanks to prevent tank uplift. The exposed concrete and just below the water line will also be coated. The limits of the structural inspection and rehabilitation include within the concrete tank structures only. Railing will be replaced; limits include these clarifiers and the final clarifier influent channel. The individual influent channels into each of Final Clarifier Nos. 1 through 3 also require improvements to eliminate this area overtopping during peak flows. The clarifier drive mechanisms are monitored by SCADA. Instrumentation and controls (i.e. over -torque alarm) will be provided, and HMI screens will be updated to match Final Clarifier Nos. 6 and 7. The clarifier equipment is electrically fed from their associated gallery buildings, which is currently being replaced through another City project and is assumed can be reused. Aeration Tank Nos. 1 through 4 Modifications. The WWTP has four aeration tanks with four passes each. Minor hydraulic improvements are required to prepare the aeration tanks for the future 100 mgd peak flow. The Pass 2 gates that allow step feed operation are in need of replacement. New electrically actuated gates will be provided. The current gate actuator is unreachable; a new gate type will be provided, or a platform will be provided for access. These gates are monitored and controlled by SCADA; the functionality will remain unchanged. Pass 4 of each tank includes an L-shaped effluent weir. These weirs will be lengthened in a U-shape to provide better flow distribution and reduce headloss across the weirs. In addition, the aeration influent channel that feeds the back of the aeration tanks is in need of isolation improvements for future maintenance. New stop logs will be provided for this area. As an optional service, the existing lighting for the Aeration Gallery area will be replaced and additional lights provided if determined necessary for better visibility in this area. Effluent Disinfection Chemical Expansion. The WWTP has two chlorine contact tanks. Treated effluent is chlorinated with chlorine gas and dechlorinated with sulfur dioxide gas, housed in the Chlorination/Dechlorination Building. Both chemical systems are limited in capacity. Evaporators will be provided to increase the chemical capacity. Due to the limited space in the building, this is the least cost alternative for disinfection expansion, which would entail less than 15 minutes contact time. In addition, the equipment (i.e. chlorinators, injectors), piping, valves, instruments, and appurtenances from the existing ton containers to the chlorine contact tanks will be replaced for both chemical systems to accommodate the increase system capacity. It is assumed that the existing chemical induction system (e.g. Water Champ) in the tanks can be reused for the chlorine gas system and the existing diffuser in the tanks can be reused for the sulfur dioxide system. The partition wall that supports the equipment, piping, etc. for each chemical system will be replaced. It is assumed that there is no code requirement for the two chemical rooms to be completely isolated and a similar type partition wall can be provided. Proper safety features will be provided including a new scrubber, which will be located outdoors, to remove gases from the air. The existing HVAC system will be evaluated considering the addition of the scrubber and recommendations only will be made for necessary improvements. The necessary improvements will be provided through the City's maintenance contract with a local vendor and will not be designed as part of this project. The improvements will be coordinated with the scrubber installation. Page 2 (Exhibit A — Engineer's Services) EJCDC E-500 Agreement Between Owner and Engineer for Professional Services Copyright © 2008 National Society of Professional Engineers for EJCDC. All rights reserved.