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2001-12-21_REVISION - C1981008
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2001-12-21_REVISION - C1981008
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Entry Properties
Last modified
8/24/2016 2:18:34 PM
Creation date
5/27/2009 1:47:36 PM
Metadata
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Template:
DRMS Permit Index
Permit No
C1981008
IBM Index Class Name
Revision
Doc Date
12/21/2001
Doc Name
Proposed Decision & Findings of Compliance for SL7
Type & Sequence
SL7
Media Type
D
Archive
No
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? ? <br /> <br />?Jf the 29 water rights within the surrounding area, 27 wells have intakes too deep to be affected by the <br />pit pumping induced drawdown in the overburden aquifer. These wells are installed in the Burro Canyon <br />Formation, which is below the Dakota coals that were mined. Significant shales separate the coals from. <br />the strata of the wells. Two righted wells, W-ooh and Woo, have intakes close to the elevation of the <br />bottom of the mine pit, The wells are located approximately ?,30o feet east of New Horizon 2 and will <br />not be affected by the New Horizon #1 Mine Area. At the eastern boundary of New Horizon 2, mining <br />will only extend l o feet below the water table. Therefore, drawdown impacts to these wells are expected <br />to be small. The wells are righted for irrigation water use. This area has been mined and reclaimed for <br />over ? years ago and there has not been any problem identified with these wells. <br />B} Ism act of sail material an.?rau?adwater f?ow_and recharge. The mine pit has been fully reclaimed <br />for many years in the New Horizon l area. A potential long-term impact to the local groundwater flow <br />is the length of time necessary for resaturation of the spoil material and reestablishment of a flow <br />gradient. Another potential impact is an Increased recharge into the spoil from precipitation and irrigation, <br />resulting in spoil springs developing downgradient. These springs may have acid conditions and high <br />dissolved solids. <br />Spoil material at the New Horizon 1 mine has increased permeability in comparison to the original <br />overburden. The hydraulic conductivity ??) of the spoil, as measured in well CW-N27, is 4o ft?day, <br />which is far greater than any measurement made in the overburden. ? values in the overburden generally <br />range from 3.o to 5.5 ftlday. The New Horizon #1. site has had continued seasonal irrigation from the <br />North Lateral ditch and a secondary ditch that flows immediately north of the New HarizH #l reclaimed <br />areas, Water from irrigation and some added precipitation has moved through the spoil and saturated it <br />until it discharges at the low point of the base of the coal at the Spoil Spring and the fond o01 discharge. <br />Flow from this point fluctuates in response to the use of irrigation. <br />Utilizing several resources, the following recharge data has been calculated: 2" from rain and snowmelt, <br />i 3" from irrigation and 1" from underburden and overburden recharge at the uphill spoilloverburden <br />contact. Total long-term recharge is therefore l ?" per year. These predictions are approximate but suffice <br />in predicting the behavior of the groundwater in the spoil. <br />A spoil porosity of l5% was determined for the overburden. <br />Spoil spring discharge (Spoil Spring ?echarge? - (Seepage into ?,Qw 1rVall? <br />Seepage into the Low Wall is approximately l 8 °?o of the total recharge. Spoil Spring Discharge is <br />approximately 82°1 of the total recharge. ?. the year ?OOO, the NPDES ool discharge at the New Horizon <br />#l Mine showed an average flow of 271,000 gallons per day or 3Z0 acre-feet per year. The NPDES ool <br />discharge is far practical purposes composed entirely of spoil water. <br />Overall, there should be no detrimental impacts from the mining operation on groundwater flow and <br />recharge rates. Ground water flow and recharge in the spoil material will be increased, since the <br />overburden aquifers have historically had very low flow rates and also poor quality. These aquifers have <br />not been used for any wells in the surrounding area and cannot be considered a water resource. The <br />ground water aquifers below the Dakota coals, in the Burro Canyon Formation, are used in surrounding <br />wells and have better water quality but will not be affected by the mining and reclamation of this site. <br />Shale layers below the mined coals prevent interaction between the spoil and these aquifers, which get <br />their recharge from long distances away from the mine operation.
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