EVALUATION OF IMPROVEMENTS TO PROVIDE ENHANCED TREATMENT RELIABILITY FOR A 160 MGD DIRECT FILTRATION WATER TREATMENT PLANT

The City of Phoenix in Arizona is a large metropolitan city experiencing tremendous population growth. Because of increasing demands for potable water and decreasing excess capacity of existing plants, the City has studied alternatives for increasing available water production, including building new plants and increasing reliability at existing plants. As a result of the study, the City decided to implement a reliability improvement project at the Union Hills Water Treatment Plant (UHWTP), an existing 160 mgd direct filtration plant. The UHWTP historically has experienced raw water quality variations that have decreased the deliverable capacity of the plant. The objective of the improvements project is to increase the reliability of the plant to produce 160 mgd finished water production even during poor raw water quality events. This paper discusses the implementation of this project.The improvements project components include: replacing the media and underdrains in 32 existing filters, installation of four new filters, retrofitting an existing large raw water impoundment with new inertial flocculators and a sedimentation basin (pretreatment facilities), expansion of an existing used water recovery system, installing new ancillary chemical feed facilities, and constructing new solids handling facilities. The improvements project incorporates several innovative components along with a “fast track” schedule required by the City for implementation. To speed the project delivery, the City preselected a “Construction Manager @ Risk (CM@Risk)” at the beginning of the project. The CM@Risk will provide design and constructability reviews while the Engineer prepares traditional 50%, 90% and 100% plans and specifications submittals. The improvements project work will be constructed in three phases to speed delivery.Innovative process considerations for the improvements project include: installation of an oscillating sludge scraper system versus traditional circular or chain and flight sludge collectors, optimizing sludge handling procedures for disposal at an adjacent sludge injection site, and installation of mechanical dewatering system to process chemical sludge produced from enhanced coagulation operations.