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4. Geology and Soils - The property is located along <br />the S. Platte River in - a Quaternary age, Piney <br />Creek alluvial deposit. The eastward dipping beds <br />_.of Upper Cretaceous age are overlain at an <br />- angular unconformity by the Pine Creek alluvium. <br />The sand and gravel encountered in the Piney <br />Creek alluvium are a result of water erosion and <br />redeposition of rock material from the front <br />range of the Rocky Mountains. The deposition <br />occurred during a time when the river was much <br />larger than it is now. This type of material is <br />typically found from south of Denver to the <br />Colorado state line along the South Platte River. <br />Along this section of the river, the deposit has <br />60% rock to 40% sand ratio and averages 15 feet <br />deep. Soils on the site are Lw-Loamy alluvial <br />land, Tc-Terrace Escarpments, Wt-Wet Alluvial <br />Land, MISLD-Gravel pits. These soils have a depth <br />of 1-3' over the underlying sand and aggregate <br />material, and the depth to underlying bedrock is <br />15'+. For more information see page 4 and EXHIBIT <br />I and J (pages 21-37) of the DRMS Application. <br />5. Hydrology - There are no water features on the <br />site. The ground water depth is 5-10'+, depending <br />upon the season, area of the site, and irrigation <br />in the area. The natural topography of the site <br />slopes to the north and northwest, but storm <br />water in this direction has been blocked by the <br />City of Thornton's reservoir construction. The <br />City of Thornton has installed a drain system to <br />carry storm water and underground alluvial water <br />to the north around the reservoir. The nearest <br />watercourse is the S. Platte River approximately <br />1 mile to the west, but. the property is not <br />within the 100-year floodplain of the S. Platte <br />River. During the initial mining and reclamation <br />(filling) activities, storm water falling within <br />the active mining and reclamation (filling) area <br />will be retained in the two future stormwater <br />ponds along I-76 at the southwest and southeast <br />corners of the property. Prior to filling going <br />above the existing ground elE?vation along I-76, <br />these two ponds will be constructed as detention <br />ponds to detain and release storm water in <br />accordance with County Regulations after approval <br />of the capacity and design of each pond by the <br />Department of Public Works. <br />4