Clogging due to the accumulation of suspended solids is a major constraint that limits the capacity of Orange County Water District's (OCWD) surface water recharge system. In order to decrease clogging and increase system capacity, OCWD is testing the ability of riverbed filtration to reduce suspended solids concentrations and improve recharge rates. Riverbed filtration is achieved through a shallow subsurface collector system placed approximately one meter below the surface. Filtered water from the collector system is conveyed by gravity to the receiving recharge basin. Initial results show that riverbed filtration is highly effective in removing suspended solids in the recharge water, which in turn also greatly increases the recharge capacity of the receiving basin. Some other water quality benefits are also achieved. Data collected thus far indicate that it will be cost-effective to use this approach at a larger scale to capture and recharge increased quantities of storm flow obtained from the Santa Ana River.
Barrick Goldstrike Mines Inc. (BGMI) has developed a comprehensive closure planning, materials characterization and in-situ monitoring program for the closure of its mine waste facilities. Facility closure techniques use topsoil and in-pit material to construct evapotranspiration (ET) cover systems to reduce or eliminate infiltration of meteoric water. One major facility at BGMI, the AA Leach Pad (AA Pad) has been closed. The Bazza Waste Rock Facility (WRF), which will hold about 1.75 billion metric tonnes (mt) of waste rock within an area of 950 hectares (ha), is undergoing concurrent closure over the next 10 years. Hydrologic performance of the AA Pad cover and the inventory, suitability and timing of in-pit materials dictated the ET cover design approach for the Bazza WRF.The AA Pad ET cover system was constructed in 2000 using two comparative cover systems; 1.2 m of fine-grained Tertiary-aged valley fill deposits of the Carlin formation, and 1.5 m of salvaged topsoil materials. The flux of meteoric water through the AA Pad cover was measured using in-situ vadose zone monitoring. Both covers had very low deep percolation rates, especially after vegetation matured. The AA Pad monitoring results were used to optimize the Bazza cover. First, an unsaturated flow model was calibrated to the in-situ monitoring data from the AA Pad. Next, the hydraulic properties of cover materials to be used for the Bazza cover were determined in large-diameter cores to minimize scale effects. Large scale in-situ hydraulic testing was also conducted to assess material variability. Finally, in-situ monitoring systems were installed in concurrent reclamation areas at the Bazza WRF.
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