SCADA (Supervisory Control and Data Acquisition) Systems

SCADA systems provide centralized monitoring and control of water and wastewater treatment processes through real-time data acquisition from field instruments and remote terminal units (RTUs). These systems collect data from sensors measuring flow, pressure, level, and chemical parameters, then display this information on human-machine interfaces (HMIs) while enabling operators to remotely adjust pumps, valves, and chemical feed systems. Modern municipal SCADA systems typically achieve 99.5% uptime when properly maintained and can monitor 500-2,000 data points across a 10-50 MGD facility. However, SCADA systems require significant cybersecurity investment and ongoing IT support, with annual maintenance costs often reaching $50,000-150,000 for mid-sized plants.

• Raw Water Intake Monitoring: SCADA monitors intake pumps, water levels, and turbidity at source locations 2-15 miles from treatment plants. Remote monitoring eliminates daily site visits while tracking pump performance and raw water quality changes. Connects upstream to source water sensors, downstream to high-service pumps.
• Chemical Feed Control: Automated chlorine, fluoride, and coagulant dosing based on real-time demand and residual monitoring. SCADA adjusts feed rates every 15-60 seconds, maintaining 0.2-4.0 mg/L residuals across varying flows. Critical for plants serving 5,000-250,000 people where manual adjustment creates compliance risks.
• Distribution System Management: Monitors tank levels, booster station pressures, and flow rates across 50-500 square mile service areas. Automatically starts/stops pumps based on system demand and maintains 35-80 psi throughout distribution network.
• Lift Station Control: Manages 10-50 remote wastewater lift stations, cycling pumps based on wet well levels and runtime hours. Prevents overflows during peak flows while balancing pump wear across multiple units.

Daily Operations: Operators monitor alarms, trending graphs, and equipment status from central control rooms. Typical facilities generate 20-100 alarms daily requiring acknowledgment and response. Operators adjust setpoints, start/stop equipment remotely, and verify automatic sequences are functioning properly. Most systems require operator response within 15 minutes of critical alarms.

​

Maintenance: Monthly battery testing, quarterly communication checks, and annual software backups. Requires basic electrical troubleshooting skills and manufacturer-specific training. PPE includes arc-flash protection when working in electrical panels. System integrators typically provide 2-3 days initial training plus annual refresher sessions for major software updates.

​

Troubleshooting: Communication failures account for 60% of SCADA problems, typically resolved by power cycling RTUs or replacing cellular modems. HMI freezing and slow response indicate database corruption requiring software restart. Average system lifespan is 15-20 years with major upgrades every 7-10 years as operating systems become obsolete.

• Human Machine Interface (HMI): Touch-screen workstations running specialized software (Wonderware, FactoryTalk) displaying real-time process graphics. Typically 21-32" industrial monitors with NEMA 4X ratings for harsh environments. Selection based on operator count and complexity of graphics required.
• Programmable Logic Controllers (PLCs): Allen-Bradley ControlLogix or Schneider Modicon units processing 500-5,000 I/O points. Rack-mounted systems with redundant processors for critical applications. Size based on total instrument count and required scan times (typically 10-50 milliseconds).
• Remote Terminal Units (RTUs): Ruggedized controllers for unmanned sites, handling 16-128 I/O points with cellular/radio communications. ABB, Schweitzer Engineering models withstand -40°F to 165°F operating ranges. Selected based on communication distance and power availability.
• Communication Network: Fiber optic, cellular, or licensed radio systems connecting 5-50 remote sites. Redundant paths for critical facilities with 99.5% uptime requirements.

• System Architecture Parameters: I/O Point Count: 500-5,000 points for 0.5-50 MGD plants (analog inputs, digital outputs, status monitoring); Communication Range: Up to 25 miles for remote lift stations and wells via radio/cellular; Scan Rate: 1-5 second updates for critical processes, 15-60 seconds for trending data; Historical Data Storage: 1-5 years on-site, with 13-month regulatory compliance minimum
• Performance Requirements: System Availability: 99.5% minimum uptime with redundant servers for plants >5 MGD; Response Time: <2 seconds for alarm acknowledgment, <5 seconds for control commands; Accuracy: ±0.25% for flow measurements, ±1% for level transmitters; Network Bandwidth: 10-100 Mbps depending on video integration and remote access needs
• Environmental Specifications: Control Room: 32-104°F operating range, <95% relative humidity; Field Devices: NEMA 4X enclosures, -40 to 140°F for outdoor installations; Power Requirements: 120/240V with 8-hour UPS backup minimum; Lightning Protection: IEEE C62.41 Category C surge protection for all field I/O

• Centralized vs. Distributed Architecture? Plants >10 MGD typically require distributed PLCs with centralized HMI. Consequence of wrong choice: $50,000+ retrofit costs and operational blind spots during system failures. Need: detailed I/O count, geographic layout, and operator staffing levels.
• What Level of Redundancy is Required? Critical processes (disinfection, high-service pumping) need hot-standby systems. Plants >25 MGD require fully redundant servers and networks. Wrong decision consequences: regulatory violations during outages, potential $100,000+ in lost water production. Need: criticality analysis and acceptable downtime limits.
• Proprietary vs. Open Protocol Communication? Open protocols (Modbus, DNP3) cost 15-20% more initially but reduce long-term vendor lock-in. Proprietary systems limit future expansion options and increase maintenance costs by 25-40%. Need: 20-year lifecycle cost analysis and integration requirements.
• Local vs. Cloud-Based Data Historians? Plants >5 MGD benefit from cloud historians for advanced analytics, but require robust cybersecurity. Local systems cost $30,000-80,000 less but limit remote access capabilities. Need: cybersecurity assessment and data accessibility requirements.

• Primary: Division 40 - Process Interconnections: Section 40 91 00 - Process Control and Instrumentation
• Secondary: Division 26 - Electrical: Section 26 27 00 - Data Communications Hardware (network infrastructure)

• Material/Equipment Verification: Verify PLC I/O capacity matches final instrument count; Confirm HMI hardware specifications for 24/7 operation; Check cybersecurity compliance (NIST framework)
• Installation Requirements: Dedicated HVAC for control rooms; Uninterruptible power systems (UPS) sizing; Fiber optic backbone for plant-wide communications
• Field Challenges: Existing instrument integration complications; Network infrastructure inadequacies; Operator training requirements
• Coordination Issues: Early electrical/instrumentation contractor involvement critical; Lead times: 12-16 weeks for custom HMI development

• Wonderware (AVEVA) - System Platform with InTouch HMI, dominant in 5-50 MGD plants
• Rockwell Automation - FactoryTalk suite with Allen-Bradley PLCs, strong municipal presence
• GE Digital - iFIX platform, established in larger facilities
• Inductive Automation - Ignition platform gaining traction in smaller municipalities (0.5-10 MGD) due to unlimited licensing model

• Distributed Control Systems (DCS) - Preferred for plants >25 MGD, 20-30% higher cost but better integration
• Panel-mounted HMIs - Suitable for small plants <2 MGD, 60% cost reduction but limited functionality
• Cloud-based SCADA - Emerging option for remote monitoring, reduces on-site hardware but requires reliable internet connectivity and cybersecurity considerations

Establish manufacturer support agreements early - municipal plants need 24/7 response capabilities. Consider "sister plant" arrangements where nearby facilities share SCADA platforms for cost savings on licensing and support. Standardize on single PLC family across multiple plants to reduce spare parts inventory. Budget 15-20% of hardware costs annually for software maintenance and cybersecurity updates.