Modernizing Wastewater Management

Smaller cities across the country are facing the complex challenge of supporting accelerated growth with aging or undersized infrastructure. One such example is Leander, Texas, which has recently experienced rapid development that far outpaced previous projections. GBA partnered with the City of Leander to develop a modernized, scalable collection system master plan that addresses these evolving demands. The following summary examines the tools, strategies and insights from that project, providing a roadmap for similar municipalities facing parallel challenges.

Why Leander Needed a New Plan

Only two decades ago, Leander was a small city. In 2000, Leander’s population was roughly 8,700. Today, it’s over ten times that number. Leander’s previous wastewater master plan, completed in 2017, was developed to support the City’s needs through 2035. However, a consistent 12–13% annual growth rate quickly rendered the plan outdated. The City’s population, currently around 100,000 residents, is projected to double over the next 20 years. With a Wastewater Certificate of Convenience and Necessity (CCN) area of approximately 55 square miles, less than half of which is currently served by municipal sewers, the need for a proactive, flexible approach became clear.

From Static to Dynamic Planning

Historically, Leander used spreadsheet-based models to estimate capacity and identify improvements. While common for small systems, these static tools lack the flexibility needed to plan for and respond to rapid or unpredictable growth. The new approach centered on developing a hydraulic model of the collection system using the Personal Computer Storm Water Management Model (PCSWMM) software to simulate current conditions and forecast future system needs based on incremental growth scenarios. This shift will allow the City to respond with greater agility to development requests and capacity constraints.

Phased and Scalable Implementation

A core element of the project was making it achievable within the City’s available resources. With utility revenues typically lagging behind growth, the team developed a set of phased capital improvement projects for the collection system. This will allow for gradual improvements as funding becomes available, minimizing the pressure to front-load massive investments.

Key Tools and Resources

Prioritizing Projects: Relief vs. Extension

Project identification followed two major paths

Extension Projects

New infrastructure needed to serve growth. These were mapped based on topography, expected development locations and timing.

Relief Projects

Needed to address current or future capacity constraints. These involved more detailed analysis within the hydraulic model, including free-flow simulations and statistical evaluation of system performance (e.g., manhole surcharging, flow loss). Critical surcharge conditions were defined collaboratively to guide prioritization.

Right-Sizing the Modeling Approach

While Leander adopted a citywide interceptor-focused hydraulic model, not every City requires the same level of detail. A key takeaway from the project is that modeling strategies should be tailored to each City’s size, complexity and growth trajectory. For some, simpler tools may suffice; for others, more advanced approaches such as digital twins, may become appropriate over time.

Lessons for Other Growing Cities

The success of Leander’s plan offers guidance for similar communities:

• Proactive planning can reduce long-term costs by avoiding inefficient emergency upgrades.
• Collaboration between planners, engineers and city staff ensures buy-in across departments and alignment between various City planning documents.
• Tools like GIS and hydraulic models are most effective when regularly updated and grounded in field-collected data.
• Phased implementation enables smaller municipalities to strike a balance between growth ambition and fiscal responsibility.

GBA’s work in Leander demonstrates that even smaller cities can adopt robust, data-driven wastewater management strategies to meet the demands of rapid growth. By building a flexible framework that integrates GIS, planning resources, flow monitoring and scalable modeling, cities can prepare not just for today’s challenges but for the growth of the future.