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A Regional Analytic Element Model to Investigate the Extent of Drawdowns on the Groundwater Flow Regime due to the Dewatering of the Proposed Crandon Mine
Large scale regional modeling has been conducted to assess the extent of the
impact on the groundwater flow regime of the projected dewatering of a zinc and
copper mine near Crandon, Wisconsin. In addition, modeled base flow values
for Swamp Creek have been used to eliminate the average areal recharge rate
due to precipitation. The program GFLOW, used for the modeling, is a single layer analytic element
model for Dupuit-Forchheimer flow. Earlier modeling efforts included
a detailed seven layer, three-dimensional finite difference model (MODFLOW)
developed by the applicant for the mining permit. While GFLOW modeling
lacks the local hydrogeological detail of the MODFLOW model, its large
regional extent allows the investigation of potential dewatering effects beyond
the boundary of the applicant's MODFLOW model. The GFLOW modeling suggests that the dewatering may lower the groundwater
elevations beyond the applicant's 1996 MODFLOW boundaries, up to
one foot west of Pickerel Creek and to more than one foot east of Walsh Lake
and St. John's Lake. The drawdowns stay within the 1998 revision of the applicant's
model boundaries, except west of Pickerel Creek. Comparing modeled
base flow in Swamp Creek with measured streamflow suggested an average
aquifer recharge rate of approximately 10 inches per year.
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