System

{{entity:Water Treatment Plant}} — 50 ML/day municipal water treatment plant, session 210. Four remaining subsystems decomposed this session: {{entity:SCADA and Instrumentation Subsystem}}, {{entity:Electrical Power and Emergency Generation Subsystem}}, {{entity:Sludge Handling Subsystem}}, and {{entity:Treated Water Storage and Distribution Pumping Subsystem}}. All 10 subsystems now have component decompositions. Status advanced to first-pass-complete with 210 requirements, 195 trace links, and 51 verification entries across 6 documents. The project is ready for QC review.

Decomposition

The {{entity:SCADA and Instrumentation Subsystem}} was prioritised first because it has the most cross-subsystem interfaces — every process area PLC, analyser, and motor controller connects through it. Six components: {{entity:Master SCADA Server and Historian}} {{hex:50A47218}}, {{entity:Distributed PLC Network}} {{hex:51B77218}}, {{entity:Process Instrumentation Field Network}} {{hex:54855018}}, {{entity:Operator HMI Workstations}} {{hex:D4ED7038}}, {{entity:Industrial Network Infrastructure}} {{hex:50A57018}}, and {{entity:Remote Telemetry and Reporting Gateway}} {{hex:51E57A18}}. The architecture follows a distributed PLC model where each process area maintains autonomous control even when the SCADA server is unreachable — a deliberate choice over a monolithic DCS to eliminate the server as a single point of failure.

flowchart TB
  FN["Process Instrumentation Field Network"]
  PLC["Distributed PLC Network"]
  NET["Industrial Network Infrastructure"]
  SRV["Master SCADA Server and Historian"]
  HMI["Operator HMI Workstations"]
  RTG["Remote Telemetry and Reporting Gateway"]
  FN -->|4-20mA HART and Modbus RTU| PLC
  PLC -->|Ethernet/IP fibre backbone| NET
  NET -->|OPC-UA process data| SRV
  SRV -->|HMI screens and alarms| HMI
  HMI -->|Operator commands| NET
  SRV -->|Telemetry and reports| RTG

The {{entity:Electrical Power and Emergency Generation Subsystem}} comprises {{entity:Main Utility Power Switchgear}} {{hex:D6B51018}} with dual 11 kV feeds, {{entity:Emergency Diesel Generator Set}} {{hex:D7D71018}} rated at 1.5 MVA, {{entity:Motor Control Centres}} {{hex:D4A55018}} distributed across six process areas, {{entity:Uninterruptible Power Supply System}} {{hex:D5D71218}} bridging the 10-second transfer gap, and {{entity:Power Distribution and Protection Network}} {{hex:44A53018}}. A single generator was selected over N+1 because the plant’s critical load fits within one unit with margin, and dual utility feeds provide the first tier of resilience.

{{entity:Sludge Handling Subsystem}} follows the conventional thickening-dewatering-disposal chain: {{entity:Sludge Holding and Thickening Tank}} {{hex:DE851018}} (400 m3), {{entity:Mechanical Sludge Dewatering System}} {{hex:56D51018}} using duty/standby belt filter presses, {{entity:Sludge Cake Storage and Disposal Hopper}} {{hex:CE851058}}, and {{entity:Supernatant and Filtrate Return System}} {{hex:55D71008}} limited to 10% of plant inflow to avoid recycling pathogens.

{{entity:Treated Water Storage and Distribution Pumping Subsystem}} closes the treatment train: {{entity:Treated Water Clear Well}} {{hex:CE851018}} (two 5 ML cells with fire reserve weir), {{entity:High-Lift Distribution Pump Station}} {{hex:56F53018}} (3+1 VFD pumps at 350-700 kPa), {{entity:Treated Water Quality Monitoring Station}} {{hex:54E75058}}, and {{entity:Distribution Network Surge Protection System}} {{hex:56973058}} using a hydropneumatic vessel.

Analysis

Lint returned 5 findings: 2 medium (degraded-mode language in {{arc:ARC-DECISIONS-007}} and {{sub:SUB-REQS-056}}), 3 low. Both medium findings are false positives — the ARC decision references degraded mode as design rationale while the quantified performance floor lives in {{sub:SUB-REQS-052}} (72-hour autonomous PLC operation), and SUB-REQS-056’s “manual override” refers to operator control actions, not a system degraded mode. Both acknowledged and stored as LINT_ACKNOWLEDGED facts. The low findings (ontological classification differences between system-level and component-level entities, and “shall” absence in ARC/VER documents) are structurally inherent and do not indicate quality issues.

Requirements

This session added 28 subsystem requirements ({{sub:SUB-REQS-049}} through {{sub:SUB-REQS-076}}), 18 interface requirements ({{ifc:IFC-DEFS-031}} through {{ifc:IFC-DEFS-048}}), 18 verification entries (VER-METHODS-034 through VER-METHODS-051), and 4 architecture decisions ({{arc:ARC-DECISIONS-007}} through {{arc:ARC-DECISIONS-010}}). All subsystem and interface requirements traced to parent system requirements. All 18 interface requirements have corresponding verification entries, maintaining 100% IFC-to-VER coverage for this session. Project totals: 210 requirements, 195 trace links, 51 verification entries, 13 diagrams.

Next

The system is now first-pass-complete. The next session should execute Flow C (QC review): review all 210 requirements for testability and ambiguity, verify PART_OF completeness across the full entity graph, check for missing cross-subsystem interfaces (particularly between Electrical Power and the process subsystems it feeds), and ensure verification coverage reaches at least 50% of combined SUB+IFC requirements. The SCADA-to-process interfaces defined in prior sessions should be cross-checked against the new SCADA component model to ensure nothing was orphaned by the more detailed decomposition.