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4-15 <br /> this reduction is approved by MLR. Parameters analyzed will <br /> be as approved in the Munger Canyon Mine permit, No. C-020-81. <br />4.3 SURFACE WATER HYDROLOGY <br />A.3.1 Regional Hydrologic Setting <br />The Salt Creek Mining Company central facilities are located <br />in the Colorado Plateau Region of west central Colorado. The <br />facilities on East Salt Creek are within the regionally steep <br />topography of the Little Book Cliffs escarpment north of the <br />Grand Valley of the Colorado River and west of Grand Junction. <br />The Colorado River, which drains this area, has eroded a deep <br />and wide valley into the surrounding mesas of the Colorado <br />Plateau. Consequently, tributary streams such as Salt Creek <br />have become moderately to deeply incised into the surrounding <br />mesas and plateaus. <br />Hydrologically, the central facilities site is located within <br />• the Grand Valley sub-basin of the upper main stem of the Colo- <br />rado River basin. Within the region, high flows typically <br />occur during May and June in response to melting snowpacks. <br />Flow rates during this period increase five to ten times over <br />those occurring during other months of the year, producing 60 <br />to 65 percent of the total annual flow. Figure 4.3-25 shows <br />the average monthly flow distribution. Low flows normally <br />occur during the winter months when surface runoff is minimal <br />and most of the flow represents groundwater discharge from the <br />watersheds (BLM, undated). <br />East Salt Creek is the major drainage system affecting the <br />central facilities site. Elevations in the drainage range <br />from 4,650 feet at the East Salt Creek near the Mack gauging <br />station to 8,800 feet at the headwaters of the East Salt Creek <br />drainage. The East Salt Creek drainage area is 197 square <br />miles at the USGS gauging station near Mack. <br />• <br />