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Where:
<br /> • Vrr= volume of water in first or intermittent fill;
<br /> • Vmm = volume of material mined from below the water table that has been filled with ground
<br /> water;
<br /> • Vbf= volume of material backfilled during the same month;
<br /> • porosity= ratio of pore volume to total volume of the material; and
<br /> • Vlp= volume of water retained in product for"not washed" material.
<br /> In past years,the gravel pits were"wet mined"; in other words, as materials were excavated from below the
<br /> water table, the pit would be simultaneously allowed to fill with groundwater. However, Everist has decided
<br /> to change this practice and will excavate Cell No.4 under dewatered conditions. Three pumps will be
<br /> operated at a combined rate ranging from 5,900 to 8,600 gallons per minute (gpm). The groundwater
<br /> pumped from Cell No. 4 will be subsequently discharged into the adjacent Cell No.3 pond.
<br /> Calculations indicate that depletions due to first/intermittent fill would be 33.4 AF per year. As stated in the
<br /> Guidelines, for pits that are mined through dewatering, intermittent fill would occur as the pit is allowed to
<br /> fill at the end of the production season. Groundwater flowing into the pit would occur at a higher rate when
<br /> immediately after pumps are shut down in mid-November,and slow down as water level in the pit increases.
<br /> For purposes of this SWSP, it has been estimated that one-half of the pit volume refills during the third and
<br /> fourth weeks of November with the remaining volume filling by the end of December.Table 3, below, shows
<br /> the monthly amounts of mined material, backfill, and corresponding first fill losses.
<br /> Table 3
<br /> Mined Material and First/Intermittent Fill Losses Estimated for 2017 and 2018
<br /> Mined Material Backfill First/Int.
<br /> Month Above GW Below GW Total Material Fill
<br /> (Tons) (Tons) (Tons) (Tons) (AF)
<br /> Jan 0 0 0 0 0.00
<br /> Feb 0 0 0 0 0.00
<br /> Mar 0 0 0 0 0.00
<br /> Apr 6,300 25,200 31,500 8,400 0.00
<br /> May 7,000 28,000 35,000 16,800 0.00
<br /> Jun 7,700 30,800 38,500 22,400 0.00
<br /> Jul 10,500 42,000 52,500 22,400 0.00
<br /> Aug 10,500 42,000 52,500 22,400 0.00
<br /> Sep 9,800 39,200 49,000 19,600 0.00
<br /> Oct 12,600 50,400 63,000 16,800 0.00
<br /> Nov 5,600 22,400 28,000 11,200 16.69
<br /> Dec 1 0 0 0 0 16.69
<br /> Total 1 70,0001 280,0001 350,000 140,0001 33.4
<br /> Note:the following assumptions were used for the calculation of First Fill Losses:
<br /> 1. Unit weight of gravel = 120 pounds per cubic foot; and
<br /> 2. Average porosity of mined material =0.30.
<br /> 4 ;;;:;RESOURCE
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