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TETRATECH RMC <br />Mr. Jeff Gregg <br />January 28, 2003 <br />Page 2 <br />alluvium is most likely claystones and sandstones of the Upper Transition Member of the Pierre <br />Shale. <br />Data for this analysis was extracted from 19 exploratory borings drilled at the site in October 1997 by <br />Terracon, seven borings drilled a[ the site in January 2003 by Tetra Tech RMC (formerly Rocky <br />Mountain Consultants, Inc., and six borings drilled by Tetra Tech RMC on the Jameson/Sewald <br />property to the north of the site. For reference we have attached a Test Boring Map showing boring <br />locations with corresponding overburden and sand and gravel thickness. The logs indicate that the <br />general subsurface profile consists of approximately three to 12 fee[ of overburden sandy clay and <br />silty sand overlying approximately 11.5 to 36 feet of sand and gravel on top of claystone and <br />sandstone bedrock. The alluvial deposit is thickest on the south parts of the mine and thinner on the <br />north part of the mine. Groundwater depths in the mine area at the time of drilling ranged from <br />approximately four to 13 feet below the 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 AREAS <br />Structures in the area and at the site are predominantly ditches; gas wells; and associated pipelines, <br />tank batteries, county roads, and overhead utilities. Some of the existing imgation ditches cross <br />through the areas to be mined. We understand Hall-Irwin plans to enter into agreements with the <br />owners of these structures regarding future use and possible relocation. Minimum mining setbacks <br />of 65 feet will be maintained until agreements are in-place. <br />All known man-made structures within 200 feet of the mined area, excluding those requiring <br />agreements with owners, are listed below: <br />Pod 1: Phase 4 and 5 <br />- Godding Hollow (imgation) Ditch approximately 75 feet to the east <br />- Rural (irrigation) Ditch approximately 40 feet to the north <br />- The Cole Ditch approximately 190 feet to the southeast <br />Pod 2: Phase 6 and 7 <br />- Mayfield (imgation) Ditch approximately 75 feet to the west <br />- Weld County Road 9'/< approximately 120 feet to the west <br />- Weld County Road 24'/< approximately 80 feet to the north <br />- Imgation ditch along edge of Weld County Road 24'/< approximately 80 feet to the northwest <br />