Show Low Wastewater Treatment Plant Evaluation and Expansion

Show Low, AZ


2.5 MGD WWTP Expansion

The City of Show Low commissioned PACE to develop an improvement plan and perform design services to upgrade its aerated lagoon wastewater treatment plant (WWTP) with a design treatment capacity of 2.46 million gallons per day (MGD). The existing WWTP process needed to be able to meet stringent effluent requirements, especially for ammonia. A previous engineering report recommended constructing a 1.75 MGD mechanical wastewater treatment facility on the existing lagoon site to meet the projected flow of 1.72 MGD required for the next 20 years. PACE was asked to confirm the recommendation by evaluating capital construction costs, operation and maintenance costs, and 20-year life cycle analyses. Recognizing that the facility already had lagoon basins, PACE recommended the design and construction of a two-basin 2.5 MGD Extended Aeration Activated Sludge (EAAS) facility using the footprint of one of the aerated lagoons. This provided the future capacity and full process redundancy for the current flow up to 1.5 MGD while minimizing earthwork construction costs. In addition, the remaining aerated lagoon serves as emergency storage for process bypass and high wet-weather flow. The new 2.5 MGD WWTP uses an EAAS process based on the Parkson Biolac® process to produce effluent quality that can meet Arizona Title 18 Best Available Demonstrated Control Technology (BADCT) effluent limits for total nitrogen (TN) of less than 10 mg/L. The facility has consistently produced effluent with TN levels less than 3 mg/L (and at times less than 1 mg/L). The WWTP Upgrade Project was completed on schedule and at a budget of less than $4 per gallon.


Water System SCADA and Controls Integration

After evaluating the City’s existing water production, storage, and distribution Supervisory Control and Data Acquisition (SCADA) system, the City hired PACE to provide engineering services to design and commission the recommended SCADA improvements for the water facilities. PACE’s Instrumentation and Controls (I&C) Group upgraded the programmable logic controller (PLC) at the existing groundwater well sites by replacing the outdated PLCs with new PLC platforms to control the wells based on well level, maintained flow rate, or constant pressure. Upgrades included the replacement of PLCs and human machine interface (HMI) touchscreens at well sites, tank sites, and booster stations and the installation of a radio network using high-speed ethernet radios between the SCADA office and each of the well and tank sites for the water system. In conjunction with the high-speed ethernet radios, PACE configured and installed an advanced cellular platform for well sites buried in no signal zones to complete the entire network. With the ability to communicate with each well site with advanced speed, PACE installed and programmed a new SCADA platform to control, adjust setpoints, monitor, collect data, and generate valuable reports on flows and totals from each well site and booster station. The client is now able to monitor and control each well site remotely using this new SCADA platform, giving them the ability to quickly respond to an emergency situation and interact with other operators to collaborate on alarm conditions in tandem through their mobile phone devices using the interactive Win911 alarm mobile application.


Key Features:

  • Facility evaluation and improvement planning with prioritization of improvements
  • Value engineering / performance specifications
  • Treatment process conversion from aerated lagoon to 2.5 MGD Biolac® EAAS
  • Alternative design approach met high effluent quality requirements while providing redundancy and emergency storage
  • Final WWTP total cost of less than $4 per gallon
  • I&C programming and integration services
  • Project within 10% of Engineer’s Cost Estimate
  • PLC upgrades at existing well sites
  • Radio network using high-speed ethernet radios
  • Advanced cellular platform
  • Installed and programmed new SCADA platform

City of Show Low

Communications, Instrumentation & Controls, PLC, SCADA, Wastewater Treatment