Merrimac WRC Stormwater Compliance Business Case
A detailed business case for upgrading stormwater infrastructure at Merrimac WRC to ensure regulatory compliance and environmental sustainability.
BUSINESS CASE PRESENTATION
Merrimac WRC Stormwater Upgrade
Presented by Dominique Sleaford
May 2026
03
Business Case Context
Background & Problem Statement
Merrimac Waste & Resource Centre (WRC) currently operating under a General Environmental Duty (GOP) with known stormwater non-compliance
Regulatory commitment to resolve non-compliance within 18 months — action is NOT optional
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
Current State
Future State (Required)
Stormwater Discharge
Uncontrolled / non-compliant
Captured & treated to standard
Water Quality
Fails contaminant thresholds
Meets regulatory licence conditions
Infrastructure
Inadequate / ad hoc
Purpose-built treatment system
Regulatory Status
Non-compliant
Fully compliant within 18 months
Integration with STP
Not integrated
Co-delivered with Stage 6 works
Regulatory compliance is a mandatory obligation — inaction is not an option.
04
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 — it does not seek to expand beyond the defined regulatory requirement.
Strategic Alignment
05
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.
06
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
Retained
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 due to insurmountable constraints.
Multi-Criteria Analysis Results
07
Option
Strategic Fit
Technical Merit
Financial & Risk
TOTAL SCORE (out of 5)
Option 1 – Do Nothing
0.4
0.6
1.2
2.2
Option 2 – Quantity Only
0.8
0.9
1.3
3.0
Option 3 – Integrated Treatment
1.6
1.8
1.2
4.6
Option 4 – Advanced + Reuse
1.4
1.6
0.8
3.8
Only Dual-Compliance Solution
Option 3 is the ONLY option addressing both water quantity AND water quality non-compliance.
Highest Score in All Categories
Option 3 achieved the top score across all three assessment categories — not just overall.
Clear Margin of Difference
0.8 points ahead of Option 4; nearly double Option 2's score.
Risk Summary
08
Option 3 is the ONLY option where NO residual risks remain above Medium after mitigation — making it the lowest-risk pathway to compliance.
Financial Summary
No Revenue Generation
Stormwater infrastructure does not generate revenue. Value is captured through compliance and avoided costs.
Avoided Fine Value
Option 1 incurs <strong style="color: #FFFFFF;">$277,888/year</strong> in regulatory penalties. Option 3 eliminates this liability entirely.
Lowest Whole-of-Life Cost
Despite higher capex than Option 2, Option 3 delivers the lowest <strong style="color: #FFFFFF;">10-year NPV</strong> across all options.
The absence of a positive BCR does not undermine the case — regulatory compliance is a non-discretionary obligation. Value is demonstrated through cost avoidance and operational enablement.
Recommended Option & Rationale
RECOMMENDED
Option 3
Integrated Stormwater Treatment
Quantity + Quality
Score: 4.6 / 5.0
Lowest NPV: $771,485
ONLY FULL-COMPLIANCE SOLUTION
The only option resolving BOTH water quantity and water quality non-compliance — all other options leave regulatory exposure.
LOWEST WHOLE-OF-LIFE COST
Delivers the lowest 10-year NPV at $771,485, driven by avoided fines of $277,888/year and lower operating costs.
MOST FAVOURABLE RISK PROFILE
No residual risks above Medium after mitigation — uniquely achieved by Option 3 alone.
DUAL STRATEGIC ALIGNMENT
Explicitly supports both the Solid Waste Strategy 2024 and the Towards Zero Waste Plan 2025–2028.
SLIDE 10
Implementation Plan
SLIDE 11
MONTH 0
Funding Approval & Project Initiation
Approve business case and release Stage 1 funding
Appoint project manager
Issue brief for design consultant
MONTHS 1–7
Detailed Design & EA Amendment
Engage design consultant via open market tender
Complete detailed engineering design
Lodge and process Environmental Authority amendment
Confirm integration scope with STP Stage 6
MONTHS 8–10
Procurement & Construction Tender
Release construction tender (open market model)
Evaluate submissions and award contract
Release Stage 2 funding tranche
MONTHS 12–18
Construction & Commissioning
Construct stormwater treatment infrastructure
Integrate with STP Stage 6 works on site
Commission system and validate compliance
Handover and close-out
<strong style="color: #C8974A;">Procurement Model:</strong> Open market tender — two stages: design consultant + construction contractor
<strong style="color: #C8974A;">Critical Path:</strong> EA amendment process (Months 1–7) is the longest lead-time item and must commence immediately upon approval
CONCLUSION & RECOMMENDATION
Approve. Fund. Initiate.
This business case recommends approval of Option 3 — Integrated Stormwater Treatment — to resolve Merrimac WRC's regulatory non-compliance within the mandated 18-month timeframe, at the lowest whole-of-life cost, and in full alignment with Council's strategic plans.
Three Immediate Next Steps:
Appoint design consultant via open market tender
Commence Environmental Authority amendment process
Confirm construction programme with STP Stage 6 team
Dominique Sleaford
- stormwater-management
- environmental-compliance
- waste-resource-centre
- business-case
- water-treatment
- infrastructure-project
- sustainability