Our team worked with Macon Municipal Utilities (MMU) to construct a headworks facility and evaluate MMU’s long-term control plan (LTCP). MMU has a combined sewer system, which conveys both sanitary wastewater and stormwater within the same pipe.
Due to this configuration, MMU’s collection system and wastewater treatment plant experiences significant variations in peak flows during wet weather events. In a combined sewer system, the wet weather flow determines the future capacity and capital costs of conveyance and treatment infrastructure. MMU has been on a journey to understanding both the dry and wet weather flow conditions in the combined sewer and leveraging that knowledge to plan projects to comply with regulations and plan for future community needs.
Partnership Goals
We worked with MMU to achieve its primary goals:
- Construct a proper headworks facility. MMU’s wastewater plant lacked a proper headworks facility, which meant combined sewer overflows (CSOs) could carry large solids, including gravel and rock, into the system, causing significant and repeated damage to the primary clarifier pumps.
- Evaluate the LTCP. MMU’s LTCP was finalized in 2009. This plan outlines a path to compliance with CSO activations and annual volume loss. MMU had completed Phases 1 and 2 of the LTCP and wanted to evaluate the effectiveness of the final phase, Phase 3.
To achieve these goals, our team completed a flow monitoring program to provide a baseline for wet weather flow generation in both the combined sewer system and a separate sewer system. Our team then developed and calibrated a hydraulic model to better understand the hydraulics in the collection system. This model completed the LTCP compliance evaluation and determined the proper headworks facility hydraulic capacity. Since the headworks is the interface point between the plant and the collection system, the hydraulic capacity had to be balanced with incoming flows as predicted by the model.
Ultimately our team was able to define current CSO activation and annual volume loss and plan improvements that would achieve LTCP compliance. This innovative modeling approach offered a refined scope of work for the headworks that aligned to operate in ideal flow conditions while considering short- and long-term flow conditions. Given the large capital cost associated with the LTCP compliance study recommendations, our team worked with MMU to develop an integrated plan. The integrated plan is a dynamic planning document MMU can use to establish and prioritize projects across the wastewater and stormwater utilities in an affordable manner.