2022-02-09_PERMIT FILE - M2021046 (7)

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resumed starting in March of 2021 to confirm whether water quality conditions have changed over time (which would not be expected as mining has not occurred and the site has not changed). The only water quality parameter that is detected regularly in the ground water monitoring wells as an exceedance of the Regulation 41 limits is manganese. Iron and pH have also exceeded Regulation 41 standards, but only periodically. The manganese exceedance was only observed in the North Well. Manganese is very common in soils and sediments and is commonly found with iron as a mineral oxide. When water interacts with these oxides they are dissolved and mobilized by the water. At the levels identified by the monitoring program,the water quality will likely result in aesthetic staining but not health concerns. Levels of manganese in the ground water can be reduced with ion exchange treatment, oxidation and filtration. Table 2.7-2 presents the available water quality results from the two wells and a comparison of the result to accepted standards. It is noted that the accepted standards apply to stream segments and not the raw water from the mine and since the dewatering water will be captured in sediment ponds before leaving the site,the indicated levels of dissolved metals will not impact live stream flow. 6.4.21(10 and 11)Surface Water Information Windy Gulch and Dawson Gulch which flow through and around the mine property locally drain the foothills to the south and surrounding the proposed mine property. These gulches are typically dry and only flow during large precipitation events. The drainage area above the mine contributing to these two gulches is estimated to be approximately 330 acres in area. Climate data collected at the Canon City weather station from 1948 through 2006 indicates that the area typically receives an average of 12.77 inches of precipitation each year with a maximum recorded annual precipitation of 23.18 inches and a maximum 1-day precipitation event of 3.21 inches. On average,the Windy Gulch and Dawson Gulch drainage received approximately 351.75 acre/feet per year combined or an average of approximately 0.98 acre-feet per day based on the weather station data and the approximate size of the drainage basin. Based on observations of flow,this average precipitation is not sufficient for the gulches to flow through the property. The maximum 1-day precipitation event introduced approximately 88.28 acre- feet into the drainage.This maximum precipitation event occurred in 1999 and there are no observations available to confirm whether the gulches flowed during this event, but it is assumed that the gulches did flow. The 100-year rain event for the property area is estimated to be 4.75 inches over a 24-hour period equating to an introduction of approximately 130.63 acre-feet into the drainage.The projected water usage at the mine would be as high as approximately 200 acre-feet per year without reuse without the ore process,which is only 57 percent of the estimated average annual flow in these drainages. Actual use will be much lower due to the reuse of water in the ore process. Grape Creek is a larger surface water feature that drains a larger basin to the west and southwest of the property.The infiltration of local precipitation and regional underflow are likely sources for the mine inflow and dewatering discharges. Grape Creek does not flow through the property and does not contribute to the site water balance. Accordingly,there is an average of approximately 351.75 acre-feet per year of precipitation that falls in the drainage above the property. The majority of this precipitation infiltrates the ground water system and the drainages that cross the property are mainly dry and, accordingly,the water flows through the property as underflow though the Precambrian material. 75