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2012-01-24_PERMIT FILE - M2011054 (4)
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2012-01-24_PERMIT FILE - M2011054 (4)
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Last modified
8/24/2016 4:47:53 PM
Creation date
2/8/2012 11:00:07 AM
Metadata
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Template:
DRMS Permit Index
Permit No
M2011054
IBM Index Class Name
PERMIT FILE
Doc Date
1/24/2012
Doc Name
Response to Adequacy Review
From
Paul Banks and Associates, LLC
To
DRMS
Email Name
THM
SSS
Media Type
D
Archive
No
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Mr. Alex Schatz <br />December 12 2008 <br />Page 6 of 11 <br />Modeling of Pits <br />Based on information obtained from Banks and Gesso, the gravel pits will be <br />mined in three phases (Phases I, IIA and IIB). The gravel resource located within each <br />phase will be mined essentially to bedrock. Each pit was modeled by placing sub - surface <br />drains at an elevation of 1 foot above the model bedrock surface. In MODFLOW, drains <br />remove water when the water table is above the elevation of the drain. The conductance <br />of each drain cell in the modeled pit areas was set to an essentially infmite value to <br />ensure that the pits were sufficiently de- watered. For this analysis, mining activities <br />during Phase I of mining were simulated with drains because the mined area in Phase I is <br />greatest and therefore drawdown during this phase of mining is expected to be greatest. <br />Figure 7 presents the location of the drain cells in Phase I of mining <br />Drawdown Simulation Results <br />The model was run to steady -state to simulate the equilibrium drawdown that <br />would be expected due to the dewatering of the site in Phase I of mining activities. <br />Figure 8 presents the drawdown that would be expected in the base -case model scenario <br />during Phase I of mining. The drawdown expected in Phase I of mining likely represents <br />the largest amount of drawdown that would be expected in each of the scenarios. <br />Drawdown in Phase I is the largest because the gravel pits will be concurrently reclaimed <br />(backfilled) as mining progresses and the Phase I pit area is the largest of the three. A <br />transient version of the model developed to simulate the drawdown that would be <br />expected during each phase of mining confirmed that the predicted drawdown during <br />Phase I of mining was indeed the greatest. The transient model also confirmed that <br />drawdown reaches approximately steady -state after 6 years of mining. During <br />subsequent phases of mining, the predicted drawdown was considerably less than that in <br />Phase I. Following mining, the heads are predicted to recover relatively quickly and <br />return to pre - mining conditions after the cessation of gravel mining <br />There are several wells in the SEO database that may potentially be impacted by <br />the dewatering activities at the mining site. Information on these wells (Permit Numbers: <br />32841, 36702, 93289, 208258, 212437, 228585, 230013, 257258, 257420, 257421) and <br />the predicted drawdown in the base -case are presented in Table 2. Although the location <br />of the wells in the SEO database is approximate, the predicted drawdown in the base -case <br />and other scenarios is greater than 5 feet at the domestic and household wells in the SEO <br />database listed under permit numbers 212437, 228585, 257258, 257420, and 257421. A <br />drawdown of greater than 5 feet at a particular well may impair the ability of this well to <br />continue pumping as it had prior to dewatering. However, all of the wells that may be <br />impacted by the dewatering listed uses are monitoring, stock, domestic or household <br />only. The pumping rate permitted for these types of wells is limited to 15 gallons per <br />minute (gpm) and it is therefore unlikely that this pumping rate will be reduced <br />substantially. Additional analysis will be required on a well -by -well basis to more <br />
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