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A) In the pre -mine condition, a large portion of the irrigation water runs off the surface and picks <br />up some TDS in the fields and is gathered in return ditches. In the post -mine condition, a large <br />portion of the irrigation water will infiltrate the backfill due to the increase in porosity. The TDS <br />and pH of the backfill water at the New Horizon North Mine is expected to approximate that of <br />the overburden water quality, resulting in minimal impact to the ground water quality. Water <br />movement through the spoil will be considerably faster than the movement in the overburden. <br />B) Spoil springs will be present at the SS #1 location and will discharge the majority of the <br />backfill water to the surface. This is an impact since it will decrease the recharge to the ground <br />water zones and increase flow at the existing spring; however, it will also quickly return water to <br />the San Miguel River by way of Tuttle Draw. The quality of water in Tuttle Draw is not suitable <br />for drinking water or irrigation water but is suitable for livestock and the spring water flow will <br />not change that. <br />Q Once the pyrite is oxidized and easily dissolved salts are washed out of the spoil, the water in <br />the spoil springs will gradually get lower in TDS until sometime in the distant future, the spoil <br />spring water quality will get better than the overburden quality. As dissolution of the backfill <br />continues, the backfill water will approach the irrigation water quality. Time periods for this to <br />occur are given later in this section. <br />Spoil Water Infiltration Into Low -wall Figure 2.05.6(3)-1 shows how infiltrating water may <br />build up in the spoil north of the Meehan Draw "protection pillar" ( Meehan Draw will not be <br />disturbed by mining) and begin to seep into the low wall. It should be noted that the mining area <br />north of Meehan Draw will be reclaimed as "dry land pasture" and will not be irrigated during <br />reclamation. Any accumulated spoil water may enter one or more of the minor sandstone beds of <br />the overburden (Dakota Sandstone) in the low wall. This annual infiltration is calculated below <br />assuming a 10' average low wall height the low wall strata, a hydraulic conductivity of 2.1 (from <br />GW -N9) and a hydraulic gradient of 0.053 (based on the water level gradients along the old <br />Peabody Highwall). <br />Seepage into Low Wall is equal to: (10' ft. average low wall height) (1900' ft. wide seepage <br />area)(hydraulic conductivity of 2.1 ft./day)(hydraulic gradient of 0.053) (1/43,560 cu. ft. per ac- <br />ft.)(365 days per year) is equal to 17.7 ac -ft per year, or an average of about 11 gpm. It is <br />strongly believed that spoil water seepage into the low wall will not have any significant impact <br />on water quality, flow rates, well usage etc. due to four reasons: <br />1) As described in this section, the water quality of the spoil water will be at a maximum 6% <br />to 10% higher in TDS than the existing overburden water quality, which is relatively <br />Section 2.05.6(3) Page 25 Sept. 2015 (TR -11) <br />