System

{{entity:Water Treatment Plant}} — 50 ML/d conventional surface water treatment serving 200,000 people. Ten subsystems, 50 components, 234 requirements at validation entry. Status entering this session: qc-reviewed. This is the outward-looking validation pass, checking whether the decomposition accurately represents a real municipal WTP.

Assessment

The decomposition is strong overall. The ten-subsystem architecture — {{entity:Raw Water Intake Subsystem}}, {{entity:Coagulation and Flocculation Subsystem}}, {{entity:Sedimentation Subsystem}}, {{entity:Filtration Subsystem}}, {{entity:Disinfection Subsystem}}, {{entity:Chemical Storage and Dosing Subsystem}}, {{entity:Treated Water Storage and Distribution Pumping Subsystem}}, {{entity:Sludge Handling Subsystem}}, {{entity:SCADA and Instrumentation Subsystem}}, {{entity:Electrical Power and Emergency Generation Subsystem}} — matches how a real plant of this class is organised. Component counts vary naturally: Chemical Storage has 8 components reflecting its complexity, while Sedimentation has 4. Performance values are in the right ballpark: 6 m/hr filtration rate, 40 mJ/cm² UV dose, T10/T ≥ 0.65 for chlorine contact, 18% cake solids from belt press. Interface requirements are detailed with correct protocols (4-20 mA HART, Modbus RTU, OPC-UA, Ethernet/IP) and realistic data rates.

All 48 interface requirements had verification entries before this session — 100% IFC coverage. The 10 architecture decision records provide genuine design rationale, not boilerplate. Stakeholder requirements cover the right actors: operators, regulators, maintenance, population served.

Six previously acknowledged lint findings remain unchanged: ontological classification differences between the abstract system entity and its physical subsystems are correct, “basin” as an engineering qualifier is valid, and SUB-REQS-056/ARC-DECISIONS-007 lint flags are false positives previously reviewed.

Gaps

Three categories of gap were identified:

Duplicates (3 pairs). {{sub:SUB-REQS-077}} and {{sub:SUB-REQS-078}} are textual clones — both describe PLC autonomous control during SCADA failure, functionally duplicating {{sub:SUB-REQS-052}}. {{sub:SUB-REQS-019}} and {{sub:SUB-REQS-021}} both specify dual-media filter turbidity performance; SUB-REQS-019 is authoritative as it includes full media specification. These duplicates accumulated across sessions 207–211 without cross-session deduplication.

Missing interface. The {{entity:Powdered Activated Carbon Feed System}} had no interface requirement defining where PAC enters the treatment train. In a real plant, PAC must be injected upstream of coagulant to allow adsorption before floc formation — a critical process sequence for taste-and-odour control.

Missing storm response. While {{sys:SYS-REQS-012}} specifies 80% turbidity reduction and storm-event performance, no subsystem requirement defined the automated response when raw water turbidity exceeds 100 NTU — specifically the coagulant dose escalation, flocculator speed adjustment, and operator alerting that a real plant’s SCADA would execute.

SUB verification coverage. Only 14 of 78 subsystem requirements had verification entries (18%). All IFC requirements were covered, bringing the combined total to 49%, but safety-critical SUB requirements for chemical containment, CT compliance, cybersecurity, and equipment interlocks lacked explicit verification plans.

Additions

Created 11 new artefacts this session:

• {{ifc:IFC-DEFS-049}}: PAC injection interface at {{entity:Rapid Mix Chamber}} — specifies upstream-of-coagulant positioning with 2-second minimum contact time. Traced to {{sys:SYS-REQS-012}}.
• {{sub:SUB-REQS-081}}: High-turbidity storm response — EARS “When” pattern requiring automated coagulant dose escalation when raw turbidity exceeds 100 NTU. Traced to {{sys:SYS-REQS-012}}.
• 7 new VER entries: {{ifc:IFC-DEFS-049}} (PAC tracer test), {{sub:SUB-REQS-009}} (containment inspection), {{sub:SUB-REQS-015}} (CT compliance), {{sub:SUB-REQS-023}} (filter-to-waste), {{sub:SUB-REQS-030}} (air scour interlock), {{sub:SUB-REQS-055}} (IEC 62443 pen test), {{sub:SUB-REQS-062}} (utility feed transfer). All with trace links.
• 2 duplicate-flagging entries ({{sub:SUB-REQS-079}}, {{sub:SUB-REQS-080}}) tagging the identified duplicates.
• Trace links added for orphaned {{sub:SUB-REQS-052}} → {{sys:SYS-REQS-008}} and {{sub:SUB-REQS-019}} → {{sys:SYS-REQS-013}}.
• CONNECTS fact stored for PAC → Rapid Mix Chamber.

flowchart TB
  WTP["Water Treatment Plant"]
  RWI["Raw Water Intake"]
  CF["Coagulation and Flocculation"]
  SED["Sedimentation"]
  FIL["Filtration"]
  DIS["Disinfection"]
  CSD["Chemical Storage and Dosing"]
  TWS["Treated Water Storage and Pumping"]
  SLU["Sludge Handling"]
  SCA["SCADA and Instrumentation"]
  EPG["Electrical Power and Emergency Gen"]
  RWI -->|Raw water| CF
  CF -->|Flocculated water| SED
  SED -->|Settled water| FIL
  FIL -->|Filtered water| DIS
  DIS -->|Disinfected water| TWS
  CSD -->|Coagulant and polymer| CF
  CSD -->|Chlorine| DIS
  SED -->|Settled sludge| SLU
  FIL -->|Backwash waste| SLU
  SCA -->|Supervisory control| WTP
  EPG -->|Power distribution| WTP

Verdict

Pass. The decomposition accurately represents a conventional surface water treatment plant. No critical gaps remain — the identified issues (missing PAC interface, storm response, duplicate cleanup) have been addressed in-session. The remaining orphaned items are 10 architecture decisions (expected — rationale documents, not traced requirements), 2 duplicate flags, and 1 identified duplicate (SUB-REQS-077). SUB verification coverage improved from 18% to 26% with the 7 new entries; the post-validation QC pass should continue expanding this.

Final project state: 234 requirements, 218 trace links, 69 VER entries, 13 diagrams, 9 baselines. Status advanced to validated. The post-validation QC session (Flow E) will verify these additions before marking complete.

Next

Post-validation QC pass should: (1) verify the 11 new artefacts from this session have correct verification attributes and traces, (2) continue expanding SUB verification coverage toward 50%, particularly for filtration and sedimentation requirements that currently have zero VER entries, (3) confirm the 3 duplicate sets are properly cross-referenced, and (4) address SUB-REQS-077 orphan status — either link it as a duplicate or delete-flag it.