Acid Sulfate Soils (ASS)

Coastal ASS

Earth Systems provides specialist expertise in the management of acid sulfate soils (ASS) and related water quality issues. From identification and characterisation of high-risk soil types and environments, through to prevention, control and treatment, Earth Systems has been providing solutions for ASS-related issues on varying scales to a diverse range of clients since 1993.

Acid sulfate soils (ASS) form naturally in both coastal and inland settings under highly reducing conditions in saturated organic-rich sediments where there is a source of sulfate and iron. In these sediments, microbial mitigated sulfate reduction results in the formation of iron sulfides, including pyrite (FeS2).


When exposed to air, either by natural means (lowering water table, drought, seasonal evaporation, erosion) or anthropogenic activity (development/excavation, agriculture, drainage development), the iron sulfides oxidise, resulting in low pH (acid) drainage and the formation of secondary iron-rich oxides, hydroxides and sulfate salts. Without appropriate management, ASS has the potential for significant environmental, human health and economic impacts, including:

aerial application (small)
  • soil acidification,
  • acid (low pH) and metalliferous drainage,
  • toxic H2S, SO2¬†and volatile organic sulfur compound (VOSC) emissions,
  • infrastructure corrosion (steel and concrete structures), and
  • reduced agriculture and aquaculture productivity.

Services Provided

Earth Systems provides specialist expertise in all aspects of the identification, characterisation, prevention, management and treatment of ASS and the associated acid and metalliferous drainage, including:

  • ASS audits, including ASS risk assessment and management system audits throughout all phases of project development,
  • Baseline studies and impact assessments associated with the disturbance/dewatering of ASS and potential acid generation,
  • Development of rehabilitation strategies,
  • Development of comprehensive site-specific ASS management, prevention and monitoring strategies that can be integrated with existing development or rehabilitation planning,
  • Identification, geochemical characterisation and classification of soils, including static and kinetic geochemical testwork, sulfur chemistry/speciation and acidity generation rate determination (OxCon testwork),
  • Water quality assessment and monitoring, including sampling protocols, total acidity and acidity load assessment, analytical data assessment and treatment reagent requirements,
  • Computer-based modelling and assessment of ASS potential including site water balances, acidity/contaminant load balances and geochemical equilibrium modelling,
  • Design/implementation of site-specific ASS prevention, control and treatment strategies, including contract treatment options, and
  • Leading-practice environmental training workshops for regulators, managers, supervisors and operators on ASS management.

Contact Earth Systems for further information on our specialist Acid Sulfate Soil management and treatment capabilities.