Laserfiche WebLink
TETRA TECH RMC <br /> Mr.Jeff Gregg <br /> March 21,2003 <br /> Page 2 <br /> Geologic mapping approximately 3,000 feet west of the site by Colton(1978)1 indicates this terrace <br /> corresponds with the Post Piney Creek Alluvium. The mapping indicates the bedrock underlying the <br /> alluvium is most likely claystones, sandstones,and possibly coal of the Laramie Formation. <br /> Data for this analysis was extracted from eight exploratory borings drilled at the site in January 2000 <br /> by Tetracon(2000)' For reference we have attached a Test Boring Map showing boring locations <br /> with corresponding overburden and sand and gravel thickness. The logs indicate that the general <br /> subsurface profile consists of approximately two to five feet of overburden silty sand overlying <br /> approximately 34.5 to 44 feet of sand and gravel on top of claystone bedrock. The logs indicate the <br /> borings encountered approximately one and one half to seven feet of weathered claystone. However, <br /> the bedrock was not sampled and was presumably logged from cuttings. Based on our experience, <br /> we expect local sandy clay overburden will also be encountered at the site. The total thickness of the <br /> alluvial deposit encountered in the borings ranges from approximately 37 to 46 feet. Groundwater <br /> depths in the mine area at the time of drilling ranged from approximately four to 12 feet below the <br /> ground surface. <br /> From a geotechnical standpoint,the sand and gravel will form most of the mine slope. These soils <br /> are generally strong and stable,particularly when dewatered. <br /> STRUCTURES WITH 200 FEET OF DISTURBED AMAS <br /> Structures in the area and at the site are ditches, Weld County Road 58,and gas wells with associated <br /> pipelines and tank batteries. Some of the gas wells,tank batteries,and gas lines are within the mine <br /> area perimeter. Mining will not encroach within 75 feet of these structures before Hall-Irwin enters <br /> into agreements with the owners of these structures regarding future use and possible relocation. <br /> All known,permanent,man-made structures within 200 feet of the mined area are listed below: <br /> ► Two gas wells,three tank batteries,and associated pipelines and access roads within the <br /> mine perimeter near Phases 1,2, 3, and 4. All of these structures will be located on <br /> berms between the mine phases with minimum setbacks of 75 feet from actual mining. <br /> ► Gas pipeline approximately 90 feet to the east of the mine. <br /> ► The Plumb irrigation ditch approximately 90 feet to the south of the mine at its closest <br /> point. <br /> ► A gas well approximately 130 feet southwest of the mine. <br /> ► A gas pipeline approximately 80 feet(at its closest point)southwest,west,northwest,and <br /> north of the mine. <br /> = Colton,R.B., 1978,-Geologic Map of the Boulder-Ft.Collins-Greeley Area,Colorado,"USGS Map 1-855G. <br /> Ten;acon,2000,"Geotechnical Engineering Report, Gravel Exploration East 18`h Street,Greeley, <br /> Colorado,"Terracon Project No.21995159. <br />