Sewer System Capacity Planning

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A comprehensive Sewer System Master Plan (SSMP) is developed by City’s for the purpose of evaluating the sewer system and provide for recommendations and upgrades that help guide a City in managing system growth. Developed recommendations are based on current and projected contributed sewer flow over time including near term, long term and ultimate buildout of the service area as well as ever changing regulations.  Master Plan project recommendations are then incorporated into the City’s Capital Improvement Program for ensuring infrastructure maintains adequate system capacity while continuing to meet regulatory requirements. 

The City began a multi-phased sewer system rehabilitation and master planning project in 2006 which included:

STEP 1:  Development of a detailed sewer system infrastructure rehabilitation project called a Corrective Action Plan (CAP) for reducing wet weather overflows by making repairs aimed at reducing the amount of storm water (rain) that enters the sewer system through cracks and openings in pipe and manholes.  The CAP report was completed in conjunction with Metro/Nashville since Brentwood and Metro/Nashville have interconnected sewer facilities.  The CAP report was presented to TDEC for approval and included a multi-year plan to rehabilitate system infrastructure including storage of infiltrated storm water;  as determine by final report and master plan.  The 2007 CAP report prepared by CDM Engineers of Nashville, and related sewer rehabilitation documents, can be found below.  For more detailed information, see the Sewer Rehabilitation Program web page.  

CAP Summary Presentation to State of Tennessee (TDEC)

TDEC Approved Corrective Action Plan 2007 Report

Corrective Action Plan Update, Presentation to TDEC, 2014

STEP 2:  Develop full system hydraulic model to aid in master planning and evaluate new development demands.  The hydraulic model developed by the City in 2015 is a very advanced, proactive approach for efficient management of system capacity and enhanced system operations through continued hydraulic updates of system flow characteristics.     The system model is a critical, valued tool utilized in development of the sewer system master plan.  The model is also utilized by staff and Hazen Engineers for evaluating large scale new development projects as they are considered for sewer service.  New project projections are forecast in the sewer system master plan and the model evaluates any significant changes from the projection.  Below is the modeling report prepared by HAZEN Engineers of Nashville.   

Sewer System Hydraulic Modeling Report

Typical Modeling Evaluation for a New Development Proposal - Evaluations of varying detail are completed for each proposed development requesting to connect to the City's water and/or sewer lines to evaluate consistency with Master Plan projections.  All new sewer connections within the Little Harpeth River Basin are only approved in compliance with conditions set forth by the 2006 Agreed Order and Moratorium.  The below SSMP includes extensive modeling to project growth for each parcel based on current zoning guidelines and/or metropolitan planning organization projections.  See SSMP report for further details on growth projections.   

STEP 3:  Development of the comprehensive Sewer System Master Plan (SSMP).   The intent of the master plan is to provide the City with a detailed plan to proactively address future collection system improvement needs. HAZEN Engineers of Nashville was contracted by the City to develop the comprehensive SSMP for both short and long-term planning.  Development of the SSMP utilized existing infrastructure data, Metro/Nashville transportation and treatment agreement criteria, collected flow monitoring data, multiple-source historical and planning records, and the above referenced hydraulic model developed specifically for the Brentwood collection system.  Selected planning horizons for Years 2020, 2030 and an Ultimate System buildout scenarios were evaluated using sewer flow projections from known development projects, Brentwood zoning of land and Nashville/Metropolitan Planning Organization (MPO) overlays;  all used congruently to ensure capacity is sustained through the entire growth forecast.  The SSMP was developed to provide a capacity level of service that corresponds with the 2-year, 24-hour design storm;  this target design storm is used by engineers and utilities and approved by Tennessee’s Department of Environment and Conservation (TDEC) for collection system master planning throughout the state of Tennessee.  Recommended improvements from the SSMP are aimed at providing the required capacity to store and convey projected flows that are predicted to occur during the design storm event.  Various types of collection system improvements were evaluated to address predicted exceedances of hydraulic capacity during the storm events, or the focus of overflows in the system.  These included on-going sewer rehabilitation, upsizing lines and pumps, and constructing equalization storage. The SSMP provides a detailed road map for needed capital improvements within Brentwood’s collection system including conveyance, storage, and rehabilitation.  The SSMPS Report completed in 2016 along with other related information can be found here: 

Sewer System Master Plan, FINAL REPORT - 2016

Sewer System Master Plan, Project Overview - Board Presentation Power Point 2015                                                                                                         see Sewer System Master Plan Informational Meeting Presentation Video for more details.

Board Meeting Minutes video for Approval of Comprehensive Sewer System Master Plan for Buildout of Sewer System                 (Resolution 2015-21)      

Other System Information:

Metro/Nashville Sewage Treatment Agreement