Capabilities › Acid Sulphate Soils
Acid Sulphate Soil Testing
NATA accredited for the full SPOCAS suite, SCr suite, field methods, and acid mine drainage testing — providing both acid trail and sulphur trail results for comparison against guideline values.
NATA
Accredited — Sydney & MPL Perth
5 day
Standard TAT (SPOCAS & SCr)
3 day
Fast TAT available
Overview
What Are Acid Sulphate Soils?
Acid sulphate soils (ASS) and sediments contain iron sulphides — most commonly pyrite — that formed naturally in waterlogged, low-oxygen conditions following the last major sea level rise approximately 10,000 years ago. In Australia, these soils are predominantly found in coastal lowlands at elevations below 5 metres above sea level.
Left undisturbed and waterlogged, these soils are harmless and are classified as Potential Acid Sulphate Soils (PASS). The problem arises when they're disturbed — through excavation, drainage, dewatering, or flood events — exposing the iron sulphides to oxygen. This triggers rapid oxidation, producing sulphuric acid that can drop soil and water pH to levels comparable to battery acid.
- Common in coastal lowlands, floodplains, estuaries, and tidal wetlands below 5m elevation
- Also found in inland areas — Murray-Darling Basin, historic lake beds, drained wetlands
- Triggered by excavation, construction dewatering, agricultural drainage, or drought
- Can also occur in marine sediments and some geological formations (acid rock drainage)
PASS vs AASS
Understanding PASS and AASS
The critical distinction in ASS management is between soils that have the potential to become acidic (PASS) and soils where acidification has already occurred (AASS). Both require testing, but the management responses differ significantly.
Both PASS and AASS require laboratory characterisation to determine the appropriate management response. Field pH alone is insufficient for regulatory submission — full SPOCAS or SCr testing is required.
PASS - Potential Acid Sulphate Soils
Contains iron sulphides but has not yet oxidised. Harmless if kept waterlogged. Management focus is on preventing exposure to oxygen — avoiding excavation, maintaining water table, or treating before disturbance.
AASS - Actual Acid Sulphate Soils
Oxidation has already occurred. pH is severely depressed. Management requires neutralisation (liming), containment of acid drainage, and monitoring of receiving waters.
SPOCAS Suite
SPOCAS - Suspension Peroxide Oxidation Combined Acidity & Sulphur
SPOCAS is the primary laboratory method for acid sulphate soil characterisation in Australia. It provides both the acid trail and sulphur trail of parameters needed for assessment under state ASS guidelines, enabling comparison to guideline values and determination of appropriate lime requirements.
Envirolab Services (Sydney) and MPL Laboratories (Perth) are both NATA accredited for the full SPOCAS suite.
- pH KCl
- TAA - Titratable Actual Acidity
- KCl extractable S, Ca, Mg
- pHox - Peroxide Oxidation pH
- TPA - Total Potential Acidity
- Peroxide extractable S, Ca, Mg
- ANCe - Effective Acid Neutralisation Capacity
- SNAS - Soil Net Acidity Score
Standard TAT: 5 working days for the full SPOCAS suite. Fast turnaround to 3 working days available — surcharges apply.
SCr Suite
SCr - Chromium Reducible Sulphur Suite
The Chromium Reducible Sulphur (SCr) method uses chromium reduction to selectively extract reduced inorganic sulphur species, most importantly pyrite. Unlike SPOCAS, which uses peroxide oxidation, SCr directly targets the sulphide fraction responsible for acid generation.
SCr is used alongside or as an alternative to SPOCAS depending on the nature of the site, the state jurisdiction's guidelines, and the specific characterisation questions being answered.
- SCr - Chromium Reducible Sulphur (pyrite and monosulphide content)
- pHF - Field pH in 1:1 soil:water
- pHFOX - pH after peroxide oxidation (field method)
- pHINC - pH of incubated sample
- ANCe and SNAS available in combination
Which suite to use? The choice between SPOCAS and SCr depends on your state jurisdiction's guidelines and project requirements. Contact us and we can advise on the appropriate testing program for your site.
Field Methods
Field & Rapid Assessment Methods
Field methods provide rapid screening results during site investigation before committing to a full laboratory program. They can be used to prioritise which samples warrant full SPOCAS or SCr analysis, and are commonly applied during initial site characterisation using the chip tray method.
- pHF - field pH in 1:1 soil:water (indicates actual acidity)
- pHFOX - pH after peroxide oxidation in field (indicates potential acidity)
- pHINC - pH of incubated moist sample
- Chip tray method - simultaneous field assessment of pHF and pHFOX across multiple samples
- AVS - Acid Volatile Sulphur (rapidly oxidisable monosulphides)
Chip tray results are indicative only and do not replace laboratory SPOCAS or SCr testing for regulatory submissions. Results should be used to guide sampling strategy, not as standalone characterisation data.
Acid Mine Drainage
Acid Mine Drainage Testing
Acid mine drainage (AMD) occurs when sulphide-bearing rocks and waste materials from mining operations are exposed to air and water. The chemistry is similar to acid sulphate soils but in a mining context — and the scale of impact can be significant, affecting receiving waterways, groundwater, and surrounding land for decades.
MPL Laboratories (Perth) is NATA accredited for Carbon and Sulphur analyses in sediments, sludges, soils and ores using the LECO solid analyser — providing in-house Total Sulphur determination as part of AMD workflows.
- Basic AMD Suite - sample prep, EC (1:2), pH (1:2), NAG and NAG pH
- NAPP - Net Acid Producing Potential (includes ANC and Total S)
- Total Sulphur, Sulphate Sulphur, Sulphide Sulphur
- NAG (Net Acid Generation) - including NAG pH, Extended Boil, Sequential, Kinetic
- ANC - Acid Neutralisation Capacity
- Metals by 4-acid digest and ICP scan
- Column leaching - free draining
Water Testing in ASS Terrane
Water Analysis in Acid Sulphate Soil Areas
Where acid sulphate soils are present, monitoring of surrounding water bodies is essential to assess the actual impact of acid drainage on receiving environments. Acidified water leaches metals from surrounding soil and rock, resulting in elevated concentrations of iron, aluminium, and other heavy metals in waterways.
- pH, EC, alkalinity, acidity, dissolved oxygen
- Sulphate, chloride, and other anions
- Iron (total, ferrous, ferric speciation), aluminium, manganese
- Dissolved and total metals - full suite available
- Suitable for receiving water monitoring programs under ASS management plans
Sampling
Sample Collection & Preservation
Correct sampling and preservation is critical for ASS analysis — exposure to air during and after collection can oxidise sulphides and alter results, particularly for PASS samples where sulphides have not yet oxidised in situ.
Holding time: Standard delivery within 24 hours is strongly preferred. Frozen or dried samples are accepted where timely delivery is not possible — contact us to confirm the appropriate preservation approach for your project before sampling commences.
Sample volume
Minimum 200g per sample collected in zip-lock bags. Seal bags tightly to minimise air contact immediately after collection.
Field preparation
Remove large shells, wood, charcoal and stones in the field. Do not remove biological material such as plant roots.
Preservation & transport
Keep samples cold. Must reach the laboratory within 24 hours of collection. Use an esky with ice for transport.
If 24hr delivery is not possible
Freeze samples immediately, or dry at 85°C and store in sealed zip-lock bags. Contact us before sampling if delays are anticipated.
Ready to get started?
Talk to our team about your soil testing requirements — fast turnaround, NATA accredited, Australia-wide.