The Problem:
A council planning condition required a landfill gas risk check before redevelopment works at an operating bus depot located near two closed municipal landfills. The aim was to close a data gap quickly and safely so construction could proceed.
Project Summary:
iEnvi proposed a lean, risk-based program that dovetailed with scheduled groundwater monitoring: reuse two onsite monitoring wells, probe three shallow hand-auger holes in grassed margins, screen accessible pits and drains, and complete an ambient surface walk-over in a single mobilisation. Results would be interpreted against EPA Victoria action levels.
The subsequent assessment included direct landfill gas monitoring at 10 locations using a calibrated GA5000 instrument, alongside a concurrent groundwater investigation to provide multiple lines of evidence. No methane was detected at any point and carbon dioxide and oxygen were within normal background ranges, confirming action levels were not exceeded.
Former landfills ──► (Groundwater: weak leachate indicators, low NH3)
│
└──► (Soil vapour: 0 ppm CH4 at wells, pits, shallow probes)
Outcome: No complete vapour migration pathway
Solution & Benefit:
Our contaminated land team executed a targeted landfill gas assessment (LFG) integrated with groundwater investigation:
Field program: two groundwater wells, stormwater pits and drains, shallow probes, and surface screening completed in one visit, aligned with the groundwater round.
Direct LFG evidence: methane not detected at any of the 10 monitoring points; all readings below EPA action levels.
Supporting groundwater evidence: very low ammonia and related indicators showed only a weak, residual leachate signature consistent with mature, stabilised closed landfills, reinforcing negligible potential for significant landfill gas generation.
Benefit: The risk from landfill gas to the proposed works and ongoing industrial use is low and acceptable. No further LFG monitoring or mitigation was recommended, and the council planning condition was satisfied—keeping the project on schedule.
