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2011-08-04_REVISION - M1999006
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2011-08-04_REVISION - M1999006
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Last modified
6/16/2021 6:12:52 PM
Creation date
8/8/2011 12:30:55 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M1999006
IBM Index Class Name
REVISION
Doc Date
8/4/2011
Doc Name
Reply to Preliminary Adequacy Review.
From
Varra Companies, Inc.
To
DRMS
Type & Sequence
TR3
Email Name
MAC
Media Type
D
Archive
No
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Dewatering Evaluation Report <br />Varra Gravel Operation <br />Kurtz Pit <br />Platteville, Colorado <br />Page 2 <br />> The saturated thickness of the aquifer prior to mine operations is 20 feet (water <br />table located ten feet below ground surface). <br />➢ The average hydraulic conductivity of the sand and gravel deposits is 170 feet per <br />day. <br />> Other than dewatering associated with mine operations no other aquifer stresses <br />such as drought and surrounding well use are accounted for. <br />➢ All groundwater solutions are steady state. <br />> The Pierre Shale which underlies the coarse alluvial deposits is an impermeable <br />barrier and the average depth from ground surface to the shale is 30 feet. <br />Overview of Drawdown Estimates <br />The hydraulic conductivity of the coarse gravel deposits is on the order of 170 feet per day <br />(Schneider, 1983) which is consistent with published values and pump test evaluations <br />conducted by the author in similar geologic settings. The average porosity of the local <br />sand and gravel deposits is estimated at 0.25. <br />The affects of dewatering on groundwater flow within the study area were evaluated by <br />use of a two- dimensional analytical groundwater flow model (TWODAN). TWODAN is a 32 <br />bit Windows program for the modeling of two- dimensional groundwater flow. The program <br />is accepted by the scientific community for evaluating two dimensional groundwater flow <br />problems and was evaluated in Groundwater, v. 36, No. 3, May -June 1998. Visual <br />MODFLOW, a three dimensional numerical model, was also used for comparison <br />purposes and generated very similar results to the analytical model. <br />A uniform flow field was defined in the model with an unconfined aquifer. The model was <br />set at approximately 281 acres (3,500 x 3,500 feet). The hydraulic conductivity of the <br />aquifer at the Varra site was estimated at 170 feet per day. The aquifer thickness was <br />modeled as 30 feet with a saturated thickness of 20 feet. The static groundwater flow <br />
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