City of Tacoma

The City of Tacoma Environmental Services operates two wastewater treatment plants — the Central plant (capacity: 139 million gallons per day) and the North End plant (30 MGD) — serving more than 208,000 residents across a 650-mile collection system with 48 pump stations. Both facilities were running on decades-old distributed control systems that no longer had manufacturer support. Limited diagnostics meant operators had to physically inspect equipment when alarms triggered, slowing response times and increasing exposure to EPA compliance risk. The absence of real-time process visibility made identifying inefficiencies across the sprawling system nearly impossible.

After a thorough evaluation process conducted with Carollo Engineers — a specialist environmental engineering firm — the city selected Rockwell Automation's PlantPAx DCS to replace the legacy systems at both plants. The preparation phase alone spanned three years, during which the team developed system standards, created new P&ID and control narratives, and mapped the transition from proof-of-concept to implementable design. Implementation ran from April 2015 through 2017. The deployment included 22 new programmable logic controllers, a Rockwell Automation Industrial Data Center providing a virtualized testing environment, and Production Intelligence and Historian Software that feeds real-time and historical process data — including pumping metrics and alarm states — directly to operators in the central control room. IoT sensor data flows continuously from plant equipment into the historian, enabling automated reporting and trend analysis without manual data collection.

The modernized DCS delivered immediate, measurable improvements across operations at both plants:

• $34,000 in annual energy savings identified by the energy management team using DCS-fed power consumption data — achieved in part by optimizing pressure setpoints to reduce pump usage
• Reduced troubleshooting time: operators shifted from reactive, physical inspections to proactive monitoring via contextualized data in the control room
• Improved alarm management: the number and severity of alarms decreased, enabling earlier intervention on potential issues
• Faster engineering deployment: the PlantPAx Library of Process Objects standardized operations and reduced integration complexity for non-Rockwell devices

Operators also gained customized, color-coded graphics aligned with each plant's existing visual standards — a flexibility that improved adoption and daily usability.

• A multi-year preparation phase — including standards development, P&ID creation, and proof-of-concept validation — is as critical as the implementation itself for DCS migrations at aging infrastructure
• Partnering with a domain-specific engineering firm (such as Carollo Engineers for water/wastewater) during technology selection reduces both technical and compliance risk
• Real-time IoT sensor data unlocks secondary value streams; in Tacoma's case, energy data alone justified $34K in annual savings that were invisible under the legacy system
• Smaller utilities can achieve enterprise-grade process control at competitive cost by selecting scalable platforms like PlantPAx rather than custom-built solutions
• A virtualized testing environment is essential when upgrading critical infrastructure — the ability to validate changes without impacting live treatment operations is non-negotiable