CMA presented at Mega Viernes Civil: Mayagüez Concordia Pump Station Rehabilitation and Execution Challenges

May 20, 2016

 

The Wastewater Concordia Pump Station (CPS) is located at the PR-102 highway, in the Concordia Sector, nearby the Mayagüez Bay. The CPS was built in 1973 and receives an estimated flow of 10 MGD of wastewater from the municipalities of Mayagüez, Hormigueros and Cabo Rojo.  The water received is transferred from the CPS to the Mayaguez Regional Wastewater Treatment Plant for final treatment and disposal.  The CPS is considered a critical installation within the Mayaguez Regional Wastewater Treatment System.  

 

Due to the raw wastewater travel distance from the serviced municipalities, the wastewater arrives to the CPS in a septic condition.  The H2S generated during the anaerobic decomposition state is released and reacts with the humidity present, forming a sulfuric acid solution that adheres to the concrete surfaces, dissolving the concrete that binds its components.  Also, due to the proximity of the CPS to the ocean, the saltpeter action accelerates the corrosion in the steel structures and exposed reinforcement.  Based on the deteriorated conditions of the CPS and the consideration of a critical installation within the Mayaguez Wastewater Treatment System, the Puerto Rico Aqueduct and Sewerage Authority (PRASA) planned for the rehabilitation improvements with the condition of maintaining a continuous operation throughout the rehabilitation process and work execution.

 

The CPS consists of a closed reinforced concrete building and an adjacent open concrete wastewater receiving pit.  The building houses the control room and maintenance operations at upper level and the transfer pit with three submergible pumps at the lower level.  The transfer pit submergible pumps are fed thru three 30” suction pipes that extend to the receiving pit.  The wastewater is received thru a 60” RCP located on the south side wall of the receiving pit.  Raw wastewater is then diverged in two concrete channels each with a coarse 2-inch screen followed by a fine 1-inch screen for solid removal that are manually cleaned.  After solid removal, wastewater is then discharged to the bottom level of the receiving pit for transfer to the Mayaguez Regional Wastewater Treatment System.

 

For the project execution, selective demolitions of structural components and reconstruction techniques with pre-cast elements were considered in order to reduce construction schedules, facilitate installation, maintain CPS operational requirements and minimize environmental risks.  In addition the use of specific concrete mixtures, material selections and surface preparation techniques were considered to withstand the septic conditions of the operation.   

 

Various rehabilitation and execution challenges of the CPS maintaining a continuous wastewater stream throughout the entirety of the rehabilitation process include: 

 

1. Design and development of a detailed execution strategy plan for the selective demolition and reconstruction work to be performed

 

2.  Evaluation of rehabilitation techniques and selection of corresponding materials

 

3.  Interagency coordination to assess continuous operation implementation within the execution strategy including consideration of emergency plans to assure minimization of any environmental risks

 

4.  Collaboration with Owner, Contractor, Inspection and Design to assure project work in accordance with execution strategy plan

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