Creek, M, Wickham, M & Gjerapic, G 2011, 'Evapotranspiration cover performance in a high desert environment, north waste rock disposal facility, Rain Mine, USA', in AB Fourie, M Tibbett & A Beersing (eds), Mine Closure 2011: Proceedings of the Sixth International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 303-312, https://doi.org/10.36487/ACG_rep/1152_33_Creek
Newmont Mining Corporation conducted a performance audit of an evapotranspiration (ET) cover constructed in 2002 at an acid generating waste rock disposal facility located at 2,000 m elevation. Based on technology available at that time, the monolithic ET cover design included approximately 0.9 m of local alluvium with native sagebrush steppe vegetation. The site receives an average of 540 mm of precipitation annually, 84% of which falls during October to April. The cover did not significantly reduce infiltration into the waste rock, as measured by a seepage collection system constructed beneath the waste rock facility. Average annual seepage following reclamation has ranged from 38,000 to 193,000 cu. m, or 13 to 44 % of annual precipitation for the 76 ha facility. Peak monthly average rates during the spring have been as much as 10 litres per second (L/s). Seepage chemistry is poor, with pH typically below 3, total dissolved solids concentration ranging from 5 to 30 g/L, and elevated metals concentrations.
Newmont proactively conducted studies of the reclamation cover including installation and monitoring of moisture sensor nests, laboratory testing, surface geophysics, monthly snow surveys, geochemical characterisation of the waste rock, and groundwater monitoring. A detailed assessment of the available design and construction data, site climate, and cover monitoring data was conducted in 2010 to assess cover performance. The study included precipitation gauge catch corrections, modelling of potential ET (PET) by aspect and slope, a direct method for computing infiltration from the moisture content sensor data, an analysis of seepage chemistry, and calibrated numerical modelling.
The assessment concluded that the compromised cover performance was due to the compounded effects from winter precipitation, snow drifting, slope and aspect influence on PET, available water holding capacity of the cover material, and cover construction unconformities. While the ET cover is able to fully reset the available water holding capacity of the cover each year, the cover profile is fully wetted each spring from snowmelt, resulting in significant infiltration into the waste rock. Newmont is using the results of this study together with an engineering analysis of alternative reclamation designs to identify a final reclamation strategy for the facility.
Allen, R.G., Pereira, L.S., Raes, D. and Smith, M. (1998) Crop evapotranspiration: Guidelines for computing crop water requirements. Irr. and Drain. Paper 56. UN-FAO, Rome, Italy.
Flerchinger, G.N. (2000) The simultaneous Heat and Water (SHAW) Model: User’s Manual, Northwest Watershed Research Center. Technical Report NWRC 2000–10, USDA Agricultural Research Service, Boise Idaho, June 15, 2000.
Fredlund, D.G. and Rahardjo, H. (1993). Soil Mechanics for Unsaturated Soils. John Wiley & Sons, Inc., New York.
Hargreaves, G.H. and Samani, Z.A. (1982) Estimating potential evapotranspiration. ASCE J. Irrig. and Drain Engr. 108(IR3), pp. 223–230.
Hargreaves, G.H. and Samani, Z.A. (1985). Reference crop evapotranspiration from temperature. Applied Engrg. in Agric. 1, pp. 96–99.
Jordan, R. (1991) A One-Dimensional Temperature Model for a Snow Cover – Technical Documentation for SNTHERM.89, Special Report No. 91–16, U.S. Army corps of Engineers, Cold Regions Research and Engineering Laboratory (CRREL), October 1991.
Neff, E.L. (1977) How Much Rain Does a Rain Gage Gage?, Journal of Hydrology 35, pp. 213–220.
Nespor, V. and Sevruk, B. (1999) Estimation of Wind-Induced Error of Rainfall Gauge Measurements Using a Numerical Simulation Numerical Simulation, Journal of Atmospheric and Oceanic Technology 16, pp. 450–464.
Penman, H.L. (1948) Natural evaporation from open water, bare soil, and grass. Proc. Roy. Soc. London A193, pp. 120–146.
Sevruk, B. (1985) Correction of precipitation measurements. Proceedings Workshop on the Correction of Precipitation Measurements, Zurich, Switzerland, WMO/IAHS/ETH, pp. 13–23.
Shapiro, R. (1987) A Simple Model for the Calculation of the Flux of Direct and Diffuse Solar Radiation Through the Atmosphere, Scientific Report No. 35, ST Systems Corporation, Lexington, Massachusetts, Under contract to Air Force Geophysics Laboratory, Report AFGL-TR-87-0200.
Walter, I.A., Allen, R.G., Elliott, R., Itenfisu, D., Brown, P., Jensen, M.E., Mecham, B., Howell, T.A., Snyder, R.L., Eching, S., Spofford, T., Hattendorf, M., Martin, D., Cuenca, R.H. and Wright, J.L. (2002) The ASCE standardized reference evapotranspiration equation. Rep. Task Com. on Standardized Reference Evapotranspiration July 9, 2002, EWRI-Am. Soc. Civil. Engr., Reston, VA, USA.
Weeks, B. and Wilson, G.W. (2004) The impact of slope and aspect on evaporation from soils in three dimensions. Proceedings 57th Canadian Geotechnical Conference, Québec, Que. Session 2D, pp. 21–27.
Weeks, B. and Wilson, G.W. (2006) Prediction of Evaporation from Soil Slopes, Canadian Geotechnical Journal 43, pp. 815–829.
Yang, D., Goodison, B.E., Metcalfe, J.R., Golubev, V.S., Bates, R., Pangburn, T. and Hanson, C.L. (1998) Accuracy of NWS 8-inch standard non-recording precipitation gauge: result of WMO Intercomparison, Journal of Atmospheric and Oceanic Technology 15, pp. 54–68.