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Joanna Williams
<br /> March 12,2018
<br /> Page 5
<br /> The dewatering pumping volume is projected to be 14 ac-ft per day at each pit (except Stage 4
<br /> which is significantly less since it is lined) and will be continuous at one or more stages at the
<br /> pits throughout the SWSP request.
<br /> A berm between Stage 6A and 6B will be constructed to allow storage to occur only within Stage
<br /> 6B. Water will be diverted into storage at Stage 6B once the berm is constructed and if free river
<br /> is available. If the call comes on the river before the desired storage depth is reached, a culvert
<br /> will be installed to drain any water above the storage volume diverted in priority into Stage 6A
<br /> where it will continue to be dewatered. Alternatively, if the depth of water in Stage 6B
<br /> increases, RMCC will only increase storage to the level that it has available augmentation
<br /> supplies to replace the resulting lagged depletions from any groundwater infiltration.
<br /> Depletion Lagging
<br /> All of the mining depletions that originate from Stages 1, 2, 6A, 6B, 3 and 4 of the Morton -
<br /> Holton Lakes Mine will be lagged to the stream. The closest live stream to Stages 1 and 2 is Big
<br /> Dry Creek, which borders the eastern boundary of Stage 1. The closest live stream to Stages 6A,
<br /> 613, 3 and 4 is the South Platte River. The lagging patterns were determined using the Glover
<br /> methodology and IDS AWAS. The following alluvial aquifer parameters were used:
<br /> • 150,000 gpd/ft transmissivity based upon pumping test data in Colorado Ground Water
<br /> Circular No. 11
<br /> • 0.20 specific yield
<br /> • 300-foot distance from the centroid of Stage 1 to Big Dry Creek, 1,150-foot distance
<br /> from the centroid of Stage 2 to Big Dry Creek, 1,360 foot, 1,720-foot, 700-foot, and
<br /> 1,000-ft distances from the centroids of Stages 6A, 613, 3, and 4, respectively, to the
<br /> South Platte River
<br /> • 7,250-foot aquifer width for Stages 1 and 2, and 8,557-foot, 8,680-foot, 7,830-foot, and
<br /> 8,400-foot aquifer widths for Stages 6A, 6B, 3, and 4, respectively, based upon CDSS
<br /> South Platte River alluvial aquifer boundary mapping
<br /> Based upon these aquifer parameters, 95 percent of the depletions accrue to the stream at Stage 1
<br /> within 5 months, within 14 months at Stage 2, within 19 months at Stage 6A, within 22 months
<br /> at Stage 613, within 11 months at Stage 3, and within 16 months at Stage 4. Normalized lagging
<br /> factors were developed for each stage to determine the timing of the lagged depletions to the
<br /> stream, as summarized in the following table.
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