Merrimac WRC Stormwater Upgrade Business Case
A comprehensive business case for upgrading stormwater infrastructure to achieve regulatory compliance and environmental sustainability at Merrimac WRC.
Merrimac WRC Stormwater Upgrade
Business Case Presentation
Dominique Sleaford
May 2026
02
Merrimac Waste & Resource Centre (WRC) currently operating under a General Environmental Duty (GED) with known stormwater non-compliance
Non-compliance spans both water quantity (volume/discharge) and water quality (contaminants)
STP Stage 6 expansion works create the critical window for integrated infrastructure upgrade
Regulatory compliance is a mandatory obligation — inaction is not an option.
03
Project Scope
IN SCOPE
OUT OF SCOPE
Stormwater capture and treatment infrastructure at Merrimac WRC
Water quality treatment system (contaminant removal)
Water quantity management (detention/retention)
Integration with STP Stage 6 construction programme
Environmental Authority (EA) amendment process
Procurement and construction management
Commissioning and handover
Broader STP Stage 6 civil works (separate project)
Potable water supply infrastructure
Site-wide drainage beyond stormwater treatment catchment
Long-term operations and maintenance (post-commissioning)
Revenue-generating reuse systems (considered but excluded)
This business case addresses stormwater compliance obligations only.
04
Strategic Alignment
Solid Waste Strategy 2024
Prioritises environmentally responsible waste management operations
Requires infrastructure investment to meet regulatory and community expectations
Supports continuous improvement in resource recovery facility performance
Option 3 directly delivers compliant, sustainable stormwater management at Merrimac WRC
Towards Zero Waste Plan 2025–2028
Commits to minimising environmental impacts from waste facility operations
Requires proactive management of leachate, stormwater and site water quality
Supports long-term operational viability of the WRC
Option 3 ensures WRC operates within environmental licence conditions through the plan period
Option 3 is the only solution that delivers full alignment with both strategic frameworks
05
Options Considered
Option
Name
Description
Reason Included
Status
Option 1
Do Nothing
Baseline comparison
Establishes cost of non-compliance ($277,888/yr in fines)
Retained
Option 2
Minimum Compliance – Water Quantity Only
Addresses discharge volume but not quality
Partial solution
Retained
Option 3
Integrated Treatment – Quantity + Quality
Full compliance solution — Wetland/bio-retention system integrated with STP Stage 6
Best overall solution
✓ RECOMMENDED
Option 4
Advanced Treatment with Reuse
Highest-spec solution
Adds water reuse capability
Retained
OPTIONS REMOVED FROM ASSESSMENT
Offsite stormwater discharge agreement — removed due to third-party dependency and regulatory uncertainty
Constructed wetland offsite — removed due to land tenure constraints and integration complexity
A structured, four-option assessment was conducted. Two further options were scoped but removed prior to MCA.
Assessment Criteria & Methodology
The Multi-Criteria Analysis (MCA) methodology used to evaluate the four options integrates three key categories to ensure a balanced, comprehensive assessment.
Technical & Engineering
Environmental & Regulatory
Financial & Operational
Each option scored 1–5 per criterion. Weighted scores aggregated to produce overall MCA score. Higher score = better outcome.
Scoring reflects weighted assessment across all three categories — not cost alone.
07
MCA Results
Option
Technical & Engineering
Environmental & Regulatory
Financial & Operational
TOTAL SCORE
Option 1: Do Nothing
1.2
1.0
1.0
2.2
Option 2: Quantity Only
2.5
1.8
2.2
3.0
Option 3: Integrated Treatment
4.8
4.9
4.2
4.6
✓ HIGHEST
RECOMMENDED
Option 4: Advanced + Reuse
3.9
3.8
3.7
3.8
Technical & Engineering
Only <strong style="color: #1E3B0E;">Option 3</strong> achieves full water quantity AND quality compliance — no other option resolves both non-compliances.
Environmental & Regulatory
Highest environmental score reflects wetland system's dual treatment function and EA alignment.
Financial & Operational
Lowest whole-of-life cost among compliant options — financial prudence without sacrificing outcomes.
<strong style="font-weight: 800; color: #1E3B0E;">Option 3</strong> achieved the highest score across ALL THREE assessment categories — not by margin, but by design.
08
Risk Summary
Risk Category
Option 1
Option 2
Option 3
Option 4
Regulatory Non-Compliance
Environmental Harm
Financial Exposure (fines)
Construction Complexity
Operational Failure Risk
EA/Approval Risk
HIGH
MEDIUM
LOW
<strong>Option 3</strong> is the ONLY option with no residual risks above Medium after mitigation. Option 1 retains multiple HIGH risks. Options 2 and 4 retain residual Medium risks. <strong>Option 3 achieves the most complete risk resolution.</strong>
Risk ratings reflect post-mitigation residual exposure. Option 3 uniquely achieves full risk resolution.
09
Financial Summary
Why No Revenue?
Stormwater infrastructure generates no direct revenue. This is standard for compliance-driven assets. Value is captured through: avoided regulatory fines ($277,888/year in Option 1), maintained operating licence (facility cannot operate non-compliant), and enabling continued STP Stage 6 operations.
Justifying the Investment
A positive BCR is not required when the investment fulfils a mandatory compliance obligation. The question is not 'does it pay?' — it is 'which option delivers compliance at lowest whole-of-life cost?' Option 3 does.
Financial value is demonstrated through cost avoidance, risk elimination, and operational continuity — not revenue generation.
Recommended<br>Option
10
OPTION 3 — Integrated Treatment: Quantity + Quality
Wetland/Bio-retention System integrated with STP Stage 6
Full Compliance Resolution
The <strong style="color: #2D5016;">ONLY</strong> option that resolves both water quantity AND quality non-compliance. Options 2 and 4 each address only part of the problem. Option 3 closes both regulatory gaps in a single investment.
Lowest Whole-of-Life Cost
At <strong style="color: #2D5016;">$771,485</strong> discounted total, Option 3 costs less than both Option 2 ($930,000) and Option 4 ($1,060,000) — and dramatically less than Option 1 ($1,388,440 in accumulated fines). Fiscal prudence AND compliance.
Most Favourable Risk Profile
The only option with <strong style="color: #2D5016;">no residual risks</strong> above Medium after mitigation. Options 1, 2 and 4 all retain unresolved HIGH or MEDIUM risks. Option 3 fully resolves the risk exposure.
Dual Strategic Alignment
Delivers compliance with both the <strong style="color: #2D5016;">Solid Waste Strategy 2024</strong> and the <strong style="color: #2D5016;">Towards Zero Waste Plan 2025–2028</strong>. No other option achieves full alignment with both strategic frameworks.
The evidence is consistent across every dimension — MCA, risk, financials, and strategy. Option 3 is the clear recommendation.
11
Implementation Plan
Funding Approval & Project Initiation
Detailed Design & EA Amendment
Procurement & Construction Tender
Construction & Commissioning
- stormwater-management
- business-case
- environmental-compliance
- infrastructure-investment
- waste-management
- sustainability
- risk-assessment