20 Years of Evapotranspiration Cover Performance of the Leach Pads at Richmond Hill Mine

• Published in: Mine water and the environment Vol. 38; no. 2; pp. 402 - 409
• Main Authors: Zhan, Guosheng, Lattin, Daniel, Keller, Jason, Milczarek, Mike
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-06-2019; Springer Nature B.V
• Subjects: Drainage; Drainage systems; Drying; Earth and Environmental Science; Earth Sciences; Ecotoxicology; Evapotranspiration; Freeze-thaw; Freeze-thawing; Geology; Hydrogeology; Industrial Pollution Prevention; Infiltration; Infiltration rate; Mine reclamation; Mineral Resources; Monitoring; Outflow; Percolation; Permeability; Precipitation; Root development; Seepage; Soil; Soil compaction; Soil permeability; Soil water movement; Technical Article; Water balance; Water Quality/Water Pollution; Wetting; Store-and-release cover; ET cover; Mine closure; Mine reclamation
• ISSN: 1025-9112; 1616-1068
• DOI: 10.1007/s10230-019-00592-7

The Richmond Hill Mine heap leach pads (HLP 1&2, and HLP 3) were reclaimed in 1996 using a three-layer evapotranspiration (ET) cover designed to limit percolation of precipitation through the facilities. HLP seepage outflow rates have been measured on an approximately weekly basis. Large seasonal and wet/dry outflow cycles have been observed. Several years after the cover system installation, increased HLP drainage rates were observed, which could be due to increased permeability of the compacted layer in response to pedogenic processes such as wetting/drying, freeze/thaw, and root development. The estimated net infiltration rate during the monitoring period is about 34% of precipitation. To evaluate the cover system efficiency, a monthly time-step, spreadsheet based water balance model was created. The model considers close inter-relation between precipitation, ET, and cover net infiltration on a monthly scale and continuous feedback of water movement in the soil-plant-atmosphere continuum. The model accurately reproduced the recorded seepage rates for the monitoring period after pedogenic processes reach a stable condition.