City Of Overland Park Tomahawk Creek Wastewater Treatment Facility

1. INTRODUCTION

The Tomahawk Creek Wastewater Treatment Facility (TCWWTF) represents one of the most significant infrastructure investments in the history of Johnson County, Kansas. Located at the intersection of dense residential development in Leawood and Overland Park, the facility recently completed a comprehensive $270 million expansion and upgrade program, transitioning from an aging trickling filter plant to a state-of-the-art biological nutrient removal (BNR) facility.

Operated by Johnson County Wastewater (JCW), the facility is critical to the region’s environmental health, treating wastewater from approximately 150,000 residents. The recent overhaul, completed in 2022, was driven by the need to treat 100% of wet-weather flows on-site—eliminating the previous reliance on diverting excess flow to Kansas City, Missouri—and to meet stringent nutrient limits for effluent discharge. Today, the 19-MGD facility stands as a model of “good neighbor” engineering, featuring one of the most advanced odor control systems in the Midwest and architectural design that harmonizes with the surrounding residential and recreational landscape.

2. FACILITY OVERVIEW

A. Service Area & Coverage

The TCWWTF serves a highly urbanized and affluent sector of the Kansas City metropolitan area, covering portions of Overland Park, Leawood, Prairie Village, and Olathe. The collection system feeding the plant is gravity-dominated, following the topography of the Indian Creek and Tomahawk Creek basins. The service area is characterized by established residential neighborhoods and high-density commercial corridors, necessitating a facility capable of handling diurnal flow variations typical of bedroom communities while managing commercial loads.

B. Operational Capacity

Prior to the 2018-2022 expansion, the facility treated approximately 7 MGD and diverted significant wet-weather flows to the City of Kansas City, Missouri, for treatment. The upgraded facility now features:

• Average Daily Design Flow: 19 MGD
• Peak Hourly Flow: 172 MGD (fully treated) / 192 MGD (hydraulic peak)

This massive increase in peak hydraulic capacity was a primary design driver, allowing JCW to cease diversion payments and retain autonomy over its wastewater operations. The plant utilizes a wet weather auxiliary treatment train to manage these extreme peaking factors effectively.

C. Discharge & Compliance

The facility discharges treated effluent into Indian Creek, a sensitive receiving water body often used for public recreation. Under the Kansas Department of Health and Environment (KDHE) supervision, the plant operates under strict NPDES permit limits, particularly regarding nutrients (Nitrogen and Phosphorus) and E. coli. The plant’s modern design ensures compliance with current regulations and anticipates tighter future limits regarding Gulf of Mexico hypoxia concerns.

3. TREATMENT PROCESS

The Tomahawk Creek facility utilizes an advanced Biological Nutrient Removal (BNR) process, replacing the previous rock-media trickling filter system. The treatment train is designed for robust performance under widely varying flow conditions.

A. PRELIMINARY TREATMENT

The headworks facility is enclosed to contain odors and noise. It features:

• Coarse Screening: Removal of large debris to protect downstream pumps.
• Fine Screening: Multi-rake mechanical screens (6mm) to remove rags and plastics.
• Grit Removal: Vortex grit chambers separate inorganic solids (sand, gravel) which are washed and dewatered before disposal.
• Flow Splitting: Automated gates direct flow between the main process train and the wet weather storage/treatment auxiliary systems during storm events.

B. PRIMARY TREATMENT

Flow moves to primary clarifiers where settleable organic solids and floatable grease are removed.

• Configuration: Rectangular chain-and-flight clarifiers are utilized for their compact footprint.
• Performance: Target removal of 60-70% TSS and 30-40% BOD, reducing the load on the secondary biological stage.
• Chemically Enhanced Primary Treatment (CEPT): During peak wet weather events, coagulants can be added to increase settling velocity and removal rates in the auxiliary train.

C. SECONDARY TREATMENT (Biological)

The core of the plant is the Activated Sludge process configured for Biological Nutrient Removal (BNR).

• Bioreactors: The aeration basins utilize a multi-stage configuration (likely A2/O or 5-stage Bardenpho style) to create anaerobic, anoxic, and aerobic zones. This facilitates:
  • Nitrification/Denitrification: Converting Ammonia to Nitrate, and then to Nitrogen gas.
  • Biological Phosphorus Removal: Encouraging Phosphorus uptake by Polyphosphate Accumulating Organisms (PAOs).

• Aeration: High-efficiency fine bubble diffusion grids powered by turbo blowers maximize oxygen transfer while minimizing energy usage.
• Secondary Clarifiers: Large circular clarifiers separate the activated sludge from the treated water. A portion of sludge is returned (RAS) to the bioreactors, while excess (WAS) is wasted to solids handling.

D. TERTIARY TREATMENT

To meet low phosphorus limits and ensure high-quality effluent:

• Disc Filtration: Deep-bed cloth media disc filters polish the secondary effluent, removing fine suspended solids and particulate phosphorus.
• Peak Flow Handling: The facility includes a specific high-rate treatment train for wet weather flows that exceeds biological capacity, often involving blending high-quality primary effluent with secondary effluent prior to disinfection, or separate high-rate clarification.

E. DISINFECTION

The facility utilizes ultraviolet (UV) irradiation for pathogen inactivation, eliminating the safety hazards associated with chlorine gas and the need for dechlorination chemicals. The UV system is designed with dose-pacing control based on flow and transmittance (UVT).

F. SOLIDS HANDLING

Significant upgrades were made to solids processing to reduce volume and hauling costs:

• Thickening: Waste activated sludge is thickened using rotary drum thickeners or centrifuges.
• Dewatering: High-solids centrifuges dewater the sludge cake.
• Disposal: Historically, JCW has utilized land application. The upgraded facility produces a stabilized cake suitable for beneficial reuse or landfilling depending on seasonal availability.

4. INFRASTRUCTURE & FACILITIES

A. Physical Plant & Architecture

The TCWWTF is unique due to its location immediately adjacent to a public golf course, walking trails, and high-value residential subdivisions. The architectural design reflects a “lodge” aesthetic, utilizing stone, timber, and sloped roofs to camouflage the industrial nature of the site. The footprint is extremely compact, requiring vertical construction and shared-wall structures.

B. Odor Control

Odor control was a critical success factor for the expansion. The facility employs a multi-stage approach:

• Containment: All primary odor sources (headworks, primary clarifiers, solids processing) are covered or housed in buildings.
• Treatment: Foul air is extracted and treated through biotrickling filters followed by activated carbon polishing units.
• Stack Dispersion: Treated air is discharged through elevated stacks to aid dispersion.

5. RECENT UPGRADES & MAJOR PROJECTS

Tomahawk Creek WWTF Expansion & Upgrade (2018-2022)

Project Budget: ~$270 Million
Delivery Method: Construction Manager at Risk (CMAR)

Key Partners:

• Owner: Johnson County Wastewater
• Design Engineer: Black & Veatch / HDR (Joint Venture)
• Construction Manager: McCarthy Building Companies

Project Drivers:

• Capacity Autonomy: The primary driver was to cease the diversion of flow to Kansas City, MO, which required expensive treatment fees and negotiation of inter-municipal agreements.
• Regulatory Compliance: The previous plant could not meet evolving nutrient removal standards imposed by KDHE/EPA.
• Aging Infrastructure: The original 1955 and 1980s infrastructure had reached the end of useful life.

Technical Highlights:

• Complex Sequencing: The project required keeping the existing plant operational while building the new facility on the same constrained site. This involved over 50 specific maintenance-of-plant-operations (MOPO) phases.
• Wet Weather Logic: The plant can ramp from 19 MGD to over 170 MGD rapidly. The hydraulic profile and pumping strategies were modeled extensively to prevent wash-out of the biological mass during storm events.
• Digital Twin: Advanced BIM (Building Information Modeling) was used during design and construction to coordinate complex piping in the compact footprint.

Results Achieved:

• Successful repatriation of all wastewater flows from the service area.
• Consistent compliance with low-level phosphorus and nitrogen limits.
• Significant reduction in community odor complaints.
• Awarded the Envision Platinum rating from the Institute for Sustainable Infrastructure (ISI).

6. REGULATORY COMPLIANCE & ENVIRONMENTAL PERFORMANCE

Permit Requirements:
The facility operates under a stringent NPDES permit that reflects the “impaired” status of many urban waterways in Kansas.

• Ammonia (NH3-N): Seasonal limits, typically < 1.5 mg/L in summer.
• Total Phosphorus (TP): Biological removal targets < 1.0 mg/L, often polished to < 0.5 mg/L.
• Total Nitrogen (TN): Monitoring and reduction goals to prevent downstream eutrophication.
• E. Coli: Seasonal disinfection limits (April – October).

Environmental Stewardship:
By earning the Envision Platinum award, TCWWTF demonstrated leadership in sustainability. The project reused 100% of crushed concrete from the demolished old plant as fill for the new structures, diverting massive amounts of waste from landfills. The upgraded treatment quality has measurably improved the water quality of Indian Creek.

7. OPERATIONAL EXCELLENCE

Staffing & Automation:
The plant is staffed by state-certified operators (KDHE Class IV Wastewater Certification preferred for leads). Operations utilize a high level of automation via SCADA, allowing for real-time monitoring of Dissolved Oxygen (DO), Oxidation-Reduction Potential (ORP), and nutrient analyzers within the basins. This allows for “feed-forward” control strategies to adjust aeration and chemical dosing (if needed) based on incoming load.

Cost Efficiency:
While the capital cost was significant, the operational cost per gallon has been optimized through the elimination of cross-jurisdictional treatment payments to Kansas City and the implementation of high-efficiency turbo blowers and LED lighting throughout the facility.

8. CHALLENGES & FUTURE PLANNING

Current Challenges

• Inflow and Infiltration (I&I): Like many older collection systems, the piping network feeding TCWWTF suffers from I&I during heavy rains, causing the massive peaking factors (19 MGD avg vs 192 MGD peak). Managing these hydraulic surges remains an operational focus.
• Workforce: The industry-wide shortage of certified wastewater operators affects all utilities; JCW actively engages in training and retention programs.

Future Planning

With the major expansion just completed, the facility is physically set for the next 25-30 years. Future planning focuses on:

• Asset Management: implementing predictive maintenance on the new high-tech equipment (membranes, sensors, UV bulbs).
• Resiliency: Continual assessment of power redundancy and flood protection, given the facility’s proximity to the creek.

9. COMMUNITY & REGIONAL IMPACT

The Tomahawk Creek project is a case study in community engagement. JCW conducted extensive public outreach, including “good neighbor” meetings, to garner support for a massive industrial project in a residential zone. The result is a facility that protects property values by eliminating odors and visually blending into the environment. Regionally, it secures wastewater independence for Johnson County, ensuring that growth in Overland Park and Leawood is not constrained by infrastructure limitations.

10. TECHNICAL SPECIFICATIONS SUMMARY

11. RELATED FACILITIES

The TCWWTF is part of the broader Johnson County Wastewater system, which includes:

• Douglas L. Smith Middle Basin WWTF: Another major facility in the system where solids from satellite plants are often processed.
• Blue River Main WWTF: Located further downstream.
• Collection System: Over 2,000 miles of sanitary sewer lines feed these facilities.

12. FAQ SECTION

Technical/Professional Questions

1. What was the primary driver for the 2022 expansion?
The need to treat 100% of wet-weather flows on-site to eliminate costly diversions to Kansas City, MO, and to replace aging 1950s-era infrastructure.

2. Does TCWWTF perform nutrient removal?
Yes. The facility utilizes Biological Nutrient Removal (BNR) to reduce Nitrogen and Phosphorus levels, supplemented by tertiary disc filtration.

3. How are wet weather peaks handled?
The plant utilizes a dual-mode operation where peak flows (up to 172 MGD) are treated through an auxiliary train that includes chemically enhanced settling and high-rate disinfection.

4. What is the Peak Peaking Factor?
The facility has an exceptionally high peaking factor (approx. 9:1 ratio of peak to average flow) due to I&I in the collection system.

Public Interest Questions

5. Why doesn’t the plant smell anymore?
The upgrade included covering all odor-generating processes and installing biological and carbon air scrubbers that capture and clean foul air before release.

6. Can the public tour the facility?
Johnson County Wastewater occasionally offers tours for educational groups and during open house events. Interested parties should contact JCW administration directly.

7. How much did the new plant cost?
The total program cost was approximately $270 million, making it one of the largest projects in county history.

8. Is the treated water safe?
Yes. The effluent meets or exceeds all safety standards set by the KDHE and is safe for discharge into Indian Creek, supporting local wildlife and ecosystem health.