Iron ore mine in the Pilbarra region, 1200 km N-NE of Perth , WA .

Semi-arid, tropical region – 320 mm annual precip. majority during cyclone season – >3000 mm potential evap./yr.

18 Mt saleable product/yr, ultimately left with 3300 Mt waste material – stockpiled in overburden storage area (OSA)

Reactive shale waste prone to spontaneous combustion and acid rock drainage (ARD)

Conventional saturated cover system not feasible for this climatic area

Use knowledge of unsaturated processes and dry cover systems to effectively segregate meteoric water from OSA

Designed to limit percolation of water through cover into OSA – store water and release it via evaporation and transpiration

Use run-of-mine (ROM) material available on site

A well designed dry cover system functions as a natural analogue

Works in concert with natural systems rather than in opposition

Test covers constructed to evaluate performance in the field

Instrumented to monitor performance criteria: net percolation, change in water storage, in situ OSA temperatures

Five test plots (TP) constructed:

TP#1 and #2 – 1-dimensional horizontal surface

	verify preliminary soil atmosphere modelling
	gain confidence in overall understanding of system

TP#3 – 2-dimensional sloping surface

quantify difference in cover performance as compared to 1-D

TP#4 and #5 – Native vegetation trials

	acquire more information on plant transpiration rates
	aid in predicting long-term cover performance

Lysimeters in cover measured positive net percolation into OSA

Changes in water storage highlight a constantly evolving system – long-term monitoring required

Data collected used to revise models and enhance understanding of the system

Specialized monitoring led to critical revisions to the cover design

Knowledge of unsaturated processes defined and corrected deficiencies in construction QA/QC

Expertise in unsaturated zone hydrology allowed for design of an effective cover over the long term