At the Peat 32 Pond near Wandoan, historic coal seam gas (CSG) operations had left a thick layer of crystallised salts across the pond floor—up to 60 cm deep in places.

Traditional advice recommended excavating and hauling 11,000 m³ of impacted soil to landfill, then importing replacement material from a borrow pit. BeneTerra took a different approach: treat the soils in place, restore the natural profile, and deliver a result that exceeded expectations.

The outcome was so successful the client nicknamed the site “the jungle.”

At a Glance

  • 11,000 m³ of soil treated in situ
  • Zero tonnes removed from site
  • Salt-impacted layer up to 60 cm deep successfully remediated
  • 2-month program from excavation to revegetation
  • Outstanding vegetation growth—full cover by spring
  • 75% cost saving compared to dig-dump-replace
  • No groundwater impact detected
  • Process was approved and audited by the Department of Environment
    and Science in Queensland

Client Context

In the early 2000s, CSG ponds were typically constructed as clay-lined containment structures. Over time, natural evaporation caused salts from the coal seam water (1,500–20,000 µS/cm) to crystallise on the pond floor. At Peat 32, the pond walls were only one metre high, meaning the accumulated salt impacted layer—up to 60 cm—sat too close to the surface to allow simple rehabilitation. Without intervention, salts would rise back to the surface through capillary action, preventing long-term vegetation growth.

A major consulting firm advised the client to:

  • Excavate and haul the 11,000 m³ of saline soil to landfill
  • Identify and open a borrow pit
  • Backfill the pond with imported soil

However, no regional landfills would accept the material due to its extreme salinity—and the nearest potential facility was more than 400 km away. The client sought a more sustainable, practical and cost-effective solution. They engaged BeneTerra based on previous successful rehabilitation programs approved by the Queensland Department of Environment and Science (now DETSI).

The Challenge

The site presented several complexities:

  • Extremely high salinity in the upper 30–60 cm of soil
  • No viable disposal pathway—landfills refused the material
  • Need for a replacement soil source if excavation proceeded
  • Requirement to rebuild a stable profile that would not cause salts to rise over time
  • Short vegetation window, with rehabilitation occurring just before winter
  • Regulatory scrutiny, including oversight by a contaminated land auditor

The site presented several complexities:

  • Extremely high salinity in the upper 30–60 cm of soil
  • No viable disposal pathway—landfills refused the material
  • Need for a replacement soil source if excavation proceeded
  • Requirement to rebuild a stable profile that would not cause salts to rise over time
  • Short vegetation window, with rehabilitation occurring just before winter
  • Regulatory scrutiny, including oversight by a contaminated land auditor

Beneterra’s Solution

BeneTerra implemented an in-situ remediation process developed in partnership with DES and proven on previous CSG sites. The approach combined soil science, precision excavation, tailored ameliorants and careful reconstruction of the soil horizon.

Key elements of the method:

  • DETAILED SOIL ASSESSMENT

    BeneTerra first mapped the vertical distribution of salts and assessed soil chemistry at depth to determine how each layer could be reused.

  • EXCAVATION AND CONTROLLED RE-PROFILING

    Machine operators worked in a coordinated pattern to:

    • Excavate subsurface material in controlled layers
    • Process and ameliorate salt-impacted soils with gypsum and other amendments
    • Rebuild the soil profile so that impacted material was returned more than 1 m below the new surface—ultimately around 2m deep
    • Re-establish a natural-like soil horizon from base to surface This ensured the final profile mimicked the chemistry and structure of undisturbed soils typically found at depth in the region.
  • SURFACE SOIL AUGMENTATION

    The topsoil material was amended to ensure good structure, moisture retention and nutrient balance to support revegetation.

  • INDEPENDENT AUDITING

    The program was regularly audited by an independent contaminated land auditor. Hundreds of soil samples were analysed during the works, followed by a final core sampling program to confirm compliance with DES-approved criteria.

  • TARGETED IRRIGATION TO ENSURE ESTABLISHMENT

    Because works were completed just prior to winter, BeneTerra installed a temporary mobile irrigation system to achieve early moisture penetration and consistent germination. works occurred outside the typical growing season, BeneTerra installed temporary irrigation for four weeks, monitoring moisture levels to ensure optimal conditions for early root development.

Implementation

The workflow was tightly choreographed:

  • Excavators and dozers worked in tandem to reconstruct the profile as
    they moved across the pond.
  • Amended soils were placed at controlled depths to ensure long-term stability.
  • Irrigation began immediately after placement, ahead of cooler weather.
  • By mid-May, soil moisture had reached depths of 100 mm, triggering early germination.
  • Within 4 weeks, grass shoots were visible.
  • By spring, the site had achieved dense, healthy ground cover—outperforming the surrounding paddocks. The client jokingly named the site “the jungle” due to the vigour of the grass growth.

Results & Impact

Rehabilitation Outcomes

  • Full vegetation cover by spring
  • No groundwater impacts recorded
  • Soil profile met all DES rehabilitation criteria
  • Soil chemistry and structure restored to a stable, productive condition

Environmental Benefits

  • Eliminated ~2,000 truck movements (material out + replacement material in)
  • Avoided landfill disposal of 11,000 m³ of saline soil
  • Protected surrounding landscapes and country roads from dust and traffic impacts

Cost & Risk Benefits

  • Approximately 75% cost saving vs dig-dump replace
  • No need for borrow pit negotiation or construction
  • Reduced heavy-vehicle risk and emissions
  • Strong alignment with landholder expectations—cattle were eager to access the rejuvenated pasture