Brushy Creek Regional Wastewater Treatment Facility East Plant Expansion

The Brushy Creek Regional Wastewater Treatment Facility East Plant is a regional wastewater treatment plant owned by the City of Round Rock, City of Cedar Park and City of Austin with the City of Leander becoming an owner in this expansion project. This project evaluated the expansion of the existing 21.5 million gallons per day (MGD) treatment facility to an ultimate average flow capacity of 40 MGD. Services provided included evaluation and subsequent design and construction phase services for the expansion.

Our team served as a subconsultant for the project, which expanded the Brushy Creek Regional Wastewater Treatment Facility East Plant from 21.5 MGD to 30 MGD, with a second planned expansion to the ultimate capacity of 40 MGD. Our scope included influent flow projections; influent screening and grit removal evaluation; floodplain modeling and site improvements; influent flow splitting and pumping; yard piping and plant water design; and effluent UV disinfection, post aeration, and metering design.

Our team reviewed historical flow data into the plant and rainfall data from nearby rain gauges to determine average dry weather, peak dry weather, and peak wet weather flows, as well as an appropriate peaking factor for the expansion. Population and flow projections were gathered from the partner cities to calculate flow projections to confirm that the expansion capacity was sufficient.

For the floodplain modeling, the team reviewed a revised hydrologic model for the Upper Brushy Creek watershed to determine a revised 100-year floodplain elevation and the floodplain limits on the plant site using HEC-RAS. As the 100-year floodplain was higher than previous, the team evaluated multiple options for protecting the site and process units from inundation in a 100-year flood. Each option was modeled and mitigation was evaluated to ensure that no impacts to the floodplain elevation were caused by any of the project improvements.

For the influent flow splitting task, the team used the flow projections from the partner Cities to calculate the ultimate influent flow via three separate interceptors. These flows were used to determine the flow splitting requirements in order to evenly distribute the total influent to two on-site lift stations with equal pumping capacity.

For the headworks evaluation, our team assessed multiple fine and coarse screen technologies, and grit removal technologies. A preliminary headworks layout was prepared for use as the basis for final design.

During the final design phase, our team was tasked with designing a 60-inch interceptor, including a flow splitting manhole, bypass pumping design for influent flows up to 42 MGD, and a trenchless crossing at depths exceeding 40 feet. Additionally, the design incorporated a new on-site lift station, approximately 45 feet deep, featuring an ultimate layout for five 200-horsepower submersible pumps (with three to be installed with this expansion) and a Fat, Oil & Grease (FOG) removal system to reduce lift station cleaning for operators. To enhance efficiency, the team evaluated septage receiving stations, selecting a design located on the plant’s exterior for future automated billing and septage screening and testing, eliminating the need for haulers to drive through the plant site.

For the new 60 MGD UV disinfection system, various technologies and equipment configurations were assessed to meet permit limits. A hydraulic model of the existing plant water system was developed to determine available flow and pressure for equipment relying on reuse water, with the City of Round Rock reuse system integrated into the plant water piping.

The team designed over 33,000 LF of 6-inch to 78-inch piping alignments around the plant site, considering existing operations to minimize impacts during expansion construction. Driveways and an on-site stormwater collection system were also designed using HEC-RAS and StormCAD modeling.