A heap leach pad is the engineered foundation on which crushed ore is stacked for cyanide leaching. It consists of an impermeable liner system (HDPE geomembrane plus geotextile and drainage layers) over a prepared subgrade, with collection pipes routing pregnant leach solution to a lined pond. Pad design is the highest-risk, highest-CapEx component of a heap leach project.
The Liner System
A typical pad uses a double-liner: HDPE primary liner over a leak-detection layer over an HDPE secondary liner over a low-permeability clay or geosynthetic clay liner. Drains route any solution that breaks through the primary liner to a leak-detection sump for monitoring.
Sizing
Pad area sized to the total ore tonnage and chosen lift height (typically 6–60 m). A 20,000 TPD operation over 10 years at 30 m lift height needs roughly 40–60 hectares of pad. Sub-pad drainage, perimeter berms, and solution-collection trenches add to the design footprint.
Geotechnical Risk
Pad failure modes include liner punctures during ore placement, slope instability of the stacked ore, and dynamic loading from seismic events. Modern pad design uses geotechnical modeling at FS / BFS level — partnership between the process engineer (KCA) and a specialized civil/geotechnical firm.
KCA Pad Heritage
KCA pad design for the original Hog Ranch heap leach (Nevada) used over 1,000,000 sq ft of PVC liner — at a total cost of just $7.7M for the entire project. Modern pad designs are larger, HDPE-based, with engineered double-liner systems and leak-detection — but the engineering discipline traces back to the projects KCA helped pioneer.
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