2013-06-18_REVISION - M1987164 (9)

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2.2 Disturbed Area Runoff The disturbed area consists of three stormwater basins. These areas are SWMP Area 1, SWMP Area 2, and SWMP Area 3, so designated as part of the stormwater management plan (SWMP), while a comparison of the runoff volume and the pond capacity can be seen in Table G -1 above. 2.3 Access Road Culvert The access road will have to cross the ephemeral drainage located to the east, requiring a culvert. The drainage area for this culvert is roughly 230 acres, including large areas of hay meadows, some dryland pasture, and the paved runways from the Yampa Valley Regional Airport. A figure showing the drainage area, with the curve number areas, is in Appendix 2. The runoff, time of concentration, and peak flow calculations can also be found in that appendix. The peak flow for this drainage was determined to be 7.71 cfs, based on the 100 -YR storm event of 2.60 inches, the combined curve number of 61, and an area of 230 acres. Assuming that the headwater to diameter ratio (HW/D) for a projecting culvert is 1.0, the minimum size of culvert required is 21 inches, therefore a 24 inch culvert will be installed. This culvert can be seen on Map C -2. 3. Groundwater Since the test pits did not show groundwater and there are no visible seeps or springs, groundwater is not expected to be encountered during mining. While no groundwater is anticipated to be exposed by excavation, if it is exposed, excavation will cease at an elevation of 2 feet above the groundwater level. 4. Irritation Water The land within and surrounding the permit area is not irrigated. 5. Water Consumption for the Operation The Hayden Gravel Pit is on an elevated terrace and there is no groundwater on the terrace. This is known from existing operations on the terrace further north of this site and also the lack of springs emanating from the base of the gravel anywhere on the site. There is very little moisture Hayden Gravel Pit, May 2013 G -3