Waco Metropolitan Area Regional Sewerage System

Large Diameter Interceptor Master Plan 

The Waco Metropolitan Area Regional Sewerage System (WMARSS) retained Walker Partners to evaluate their gravity wastewater interceptor collection system and develop a Capital Improvements Program (CIP). The Report and CIP lay out a road map for WMARSS to follow in order to address the current deficiencies within the existing system, while at the same placing WMARSS in a position to accommodate anticipated future growth. The CIP lists the priorities and estimated costs for the identified collection system improvements.

A majority of the problems currently observed within the existing collection system are attributable to the age, materials, and structural condition of the existing interceptors. A major source of infiltration/inflow into the system is the concrete pipe joints that are in poor condition. These joints comprise a significant percentage of the pipeline network and allow large volumes of infiltration/inflow, which is “robbing” the system of any available wet weather hydraulic capacity.

Over the last 43 years, WMARSS has not performed significant rehabilitation or reconstruction improvements on the components of the original collection system. Therefore, WMARSS initiated the study to accomplish the following:
    1. Review existing studies, report and other data.

    2. Assess the structural condition of the original collection system.

    3. Evaluate the existing hydraulic capacity of the collection system.

    4. Develop an “Immediate Needs Plan.”

    5. Develop a “3-10 Year Capital Improvements Plan.”

Walker Partners reviewed the WMARSS sanitary sewer “as-built” plans and previous studies and reports to gain institutional knowledge of the current collection system.

As part of the effort, an in-depth assessment of the wastewater system was conducted by performing above ground physical inspections and below ground manhole and pipe inspections along the entire length of the original collection system.  

Peak wet weather wastewater flows for the collection system interceptors were analyzed then used to evaluate the existing hydraulic capacity of the interceptors. Existing sewer lines were analyzed to evaluate pipe capacity to determine if they needed to be enlarged to hydraulically accommodate future flows. Proposed wastewater interceptors were preliminarily sized based upon future population projections and transfers of flows so that they will be in accordance with the design criteria set forth by TCEQ’s Chapter 317, “Design Criteria for Sewerage Systems.”

Walker Partners was responsible for presenting at a series of Policy Board Meetings that included both City of Waco staff and other Policy Board members in order to provide vital information that would allow for their full understanding of the various collection system constraints and inadequacies.

We met with and listened to WMARSS staff to acquire their extensive historical information on the wastewater system. The prioritization of the recommended list of projects was adjusted to accurately reflect the institutional knowledge of the staff as it compared to field observations performed as part of the scope of work. These efforts were made in order to validate and confirm the information provided and to make sure that WMARSS was completely satisfied with the development of the Capital Improvements Program. The final CIP projects were jointly developed with WMARSS staff and were included within one of three categories:

1. Immediate Needs - addresses critical operation and maintenance deficiencies within the existing system.

2. 3-10 Year projects - addresses pressing operation and maintenance deficiencies within the existing system.

3. Additional Near-Term Capital Improvements – addresses future capacity issues to serve projected growth areas and addresses locations with a lower overall risk of capacity deficiencies.

The Capital Improvements Plan identified a total of 21 gravity system improvement projects that will be required to accommodate future wastewater flow conditions as well as projects to address state and federal regulatory and operational requirements. The CIP estimates that $3M in improvements will be required to complete the Immediate Needs Projects. The CIP additionally estimates that $69M in improvements will be necessary to complete the 3-10 Year projects. Of significance, the CIP recommended the construction of a new LaSalle Lift Station that will not require the flows to be routed to and through the Transfer Lift Station.

The construction of this project will effectively allow the City of Waco to double the available capacity that the City can transfer to the Central Plant while providing system redundancy that will significantly reduce the hydraulic capacity, conserve the structural condition of the lift station, and reduce overall risk to the system. This is a very significant planning and operational approach for the City of Waco and WMARSS in terms of future growth and O&M.

The schedule outlined within the report proposes an orderly, methodical, and obtainable plan to clearly indicate projects that should be executed prior to beginning subsequent projects in order to provide for the needed wastewater capacity and rehabilitation measures. 

completion date: 2013

location: waco, Tx

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