Urban Tunnelling Project — Stockpile Waste Classification

Background

Trilogy was engaged to assess an excavated soil stockpile generated during a major urban infrastructure project. The material came from beneath an area where contaminated fill had previously been identified.

The key question was whether the natural soils had been affected by the overlying material, or whether they could be managed through a lower-risk disposal and reuse pathway.

The approximately 50 m³ stockpile at the bulk fill rehabilitation site, with the exposed geological profile of the quarry face visible in the background — pale lacustrine sediments over red-brown alluvial clays.

Scope of Works

The scope was kept targeted and proportionate to the decision required. Works included:

• Inspection and description of the stockpile material
• Representative sampling across the stockpile
• Laboratory analysis focused on the contaminants of concern
• Quality control checks to support the classification decision
• Assessment against relevant SA EPA waste criteria

Looking north-east across the stockpile — the scale of the receiving site's quarry escarpment illustrates the volume of material being rehabilitated with WDF inputs.

Looking south, showing the highly laminated pale lacustrine limestone and clay geology of the receiving site.

Findings

The stockpile was generally consistent with natural soils, with no obvious asbestos, staining or odour observed during inspection.

Laboratory results did not indicate material cross-contamination from the overlying hotspot. The testing supported classification of the material as Waste Fill and confirmed a suitable receiving pathway.

Outcomes

The targeted assessment resolved the disposal uncertainty and allowed the project team to manage the stockpile through the preferred pathway.

• Waste Fill classification confirmed
• Reuse pathway supported at a licensed rehabilitation site
• Construction-stage uncertainty reduced without unnecessary investigation scope