Round Rock Brushy Creek Wastewater Treatment Plant

Plummer was retained to perform master planning, preliminary design, and detailed design for an expansion of the plant from the existing capacity to 30 MGD. The plant is jointly owned by Round Rock, Cedar Park, Austin, and Leander, and provides service to Leander and Fern Bluff MUD. The service area experienced rapid growth and the Partners needed to quickly increase capacity. This work was completed in approximately 28 months, including Partner reviews and authorization of subsequent phases.

Initially, the Cities wanted to expand from 21.5 MGD to 40 MGD. During conceptual design, Plummer evaluated the existing facility, strength of wastewater being received, and flow projections provided by each city. We were able to demonstrate the cost benefits of moving forward with an interim phase of 30 MGD as opposed to a larger capital expense of expanding to 40 MGD, a savings of approximately $65 million. Plummer conducted a series of workshops with the Partners’ engineering staff and operators to select the optimal treatment process. The plant is designed to achieve a 0.5 mg/L total phosphorus limit. The selected process was anaerobic/anoxic/oxic (A2O) to achieve biological nutrient removal. 

The existing TCEQ discharge permit contained a nitrate limit due to go into effect within a year. Plummer recognized that this limit would make it difficult for the operators to maintain compliance and that the nitrate limit should not have been included in the permit. Plummer was successful in getting TCEQ to remove the nitrate limit and having the permit amended to increase the flows to 30 MGD. Plummer also re-evaluated the floodplain based on new hydrology and determined that while the increased floodplain would surround some units, they would not be inundated. Plummer made sure the 2-hour peak flow could pass through the plant given the increased tail water condition in Brushy Creek. 

The detailed plant expansion design included a new influent lift station and new preliminary treatment unit whose structures will handle flows to a 40 MGD buildout and provide improved plant hydraulics. Other improvements included a new aeration basin treatment train and secondary clarifier, modifications to the existing aeration basins to add biological nutrient treatment for phosphorus removal, increased blower capacity, expanded capacity for the UV disinfection, safer and more reliable chemical feed system improvements, and updated advanced odor control for all new facilities. Additional filter capacity was also added in the design using disk cloth media type filters to minimize costs and decrease the need for redundant equipment.

With budget top of mind, Plummer provided regular updates to the opinion of probably construction cost (OPCC) given the volatile bidding market. To mitigate some volatility, Plummer employed a preselection process for major pieces of equipment, locking in the price for equipment early and allowing the design to proceed based on the actual equipment to be installed. In addition, several improvements were bid as deductive alternates to reduce the project to fit the budget. Using the Competitive Sealed Proposal process, the low bid matched the original Conceptual Design OPCC. 

The new lift station, preliminary treatment unit and 10 MGD treatment train have been constructed and were started up in 2022. The new UV disinfection, post aeration facility and additional filtration capacity were started up in 2023. Currently the existing 20 MGD treatment trains have been rehabilitated and are treating flow, with construction close to completion on odor control, sludge storage and processing facilities. Construction for the 30 MGD expansion is almost done. Plummer is now working on new filters and new expansion to 40 MGD due to growth.