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Facilities Consolidation: Chelford City Diversion Package No. 1

The City of Houston has an ongoing program to consolidate their wastewater collection system infrastructure via construction of deep gravity interceptors. The program includes the Chelford City Diversion project, which will redirect flows currently sent to Chelford City for treatment to Houston’s Upper Braes Wastewater Treatment Plant. Hazen was selected to develop the Preliminary Engineering Report and provide design, bid, and construction phase services for Phase 1.

The 9,800 linear feet (LF) 60-inch wastewater tunnel will divert flows from the existing Alief Central Lift Station to an existing 108-inch gravity interceptor in West Houston Center Boulevard, just upstream of Upper Braes WWTP.

The 9,800 linear feet (LF) 60-inch wastewater tunnel will divert flows from the existing Alief Central Lift Station to an existing 108-inch gravity interceptor in West Houston Center Boulevard, just upstream of Upper Braes WWTP. This project will include the decommissioning of Alief Central Lift Station and will allow for the future decommissioning of three lift stations, flows from which will eventually tie directly into the Phase 1 portion of the line. An additional five lift stations will be able to be decommissioned and bypassed flows tied into other phases of the Chelford City Diversion tunnel, upstream of Phase 1.

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Base bid line items and additional allowances were included in the bid form to control costs for handling PPCA contaminated material and groundwater.

The Phase 1 project was design-bid-build and was bid in two packages: West Houston Center Boulevard to Dairy Ashford Road; and Dairy Ashford Drive to Alief Central Lift Station. 7,800 LF of the alignment is in the Westpark Drive right-of-way, with the upstream 2,000 LF in new easement through private properties, and adjacent to an existing CenterPoint Energy easement.

Based on the geologic conditions of medium to stiff clays, with occasional medium to dense clayey sands, encountered at the average tunnel depths between 55-feet and 60-feet, Hazen determined that a single pass microtunneling approach was best suited for the project.

In four locations, upstream consolidation projects are tying into our interceptor. Vortex drop units were designed to be installed at these connections to dissipate the turbulence in the incoming flows, reducing odor and corrosion-causing gas generation.

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The City's program will provide a 100-year-life gravity conveyance system with 50 MGD of wastewater capacity.The City's program will provide a 100-year-life gravity conveyance system with 50 MGD of wastewater capacity.

Project Outcomes and Benefits

  • The consolidated gravity interceptor system will simplify operation and maintenance and provide future flexibility to eliminate O&M costs associated with the operation of up to nine existing lift stations
  • A phased construction plan, aligned with a complex multi-phase traffic control plan, limiting impacts to residents and motorists
  • Strategic investment in polymer concrete manholes and vortex drop units will reduce corrosion potential and enhance system life
  • Multiple tie-ins were designed to implement the use of vortex drop units to suppress turbulence in incoming flows
  • Phase I and II Environmental Assessments identified and confirmed Potential Petroleum Contaminated Areas (PPCA) through test borings; areas were delineated and specifications for soil and groundwater handling and disposal developed
  • Fee simple right of way property acquisition for private property and CenterPoint Energy and permits obtained for multiple Harris County Flood Control District drainage bayou crossings