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November 9, 2005 <br />Carma <br />Highland Place 11 <br />9110 East Nichols Avenue, Suite 180 <br />Greenwood Village, Colorado 80112 <br />Attn: Mr. Tyler Packard <br />l~~rracon <br />Consulting Engineers 8 Scientists <br />Terracon Consultants, Inc. <br />10625 West I-70 Frontage Road Nonh, Suite 3 <br />Wheat Ridge, Colorado 60033 <br />Phone 303.423.3300 <br />Fax 303 423.3353 <br />www.terracon.com <br />Re: Supplemental Geotechnical Engineering Report <br />Proposed Slurry Cut-off Walls @ St. Vrain Development <br />Weld County Road 30 (Highway 66) and Interstate 25 <br />Weld County, Colorado <br />Terracon Project No. 25045300 <br />Terracon has completed supplemental geotechnical engineering exploration and packer <br />permeability testing for the proposed slurry cut-off walls to be located within the southern <br />portion of the St. Vrain Development. The development is located near the southeast corner <br />of Weld County Road 30 (Highway 66) and Interstate 25 in Weld County, Colorado. This <br />study was performed in general accordance with our proposal number D25050631 dated <br />August 24, 2005. A previous study was performed at the site by Terracon (same project <br />number) dated November 24, 2004, in which the depth to bedrock was determined along the <br />perimeter of the proposed lake improvement areas. This previous study was reviewed to <br />supplement the information from this study along with a preliminary report for the overall <br />development prepared by Terracon (Project No. 25045122). <br />The results of our engineering study are attached. These results include the Boring <br />Location Map, laboratory test results, Logs of Borings for the current and previous slurry wall <br />study, and the geotechnical recommendations needed to aid in the design and construction <br />of slurry cut-off walls and other earth connected phases of this project. <br />As outlined in our previous and current study, the surface and subsurface materials at the <br />site consisted of native soils and bedrock. Native soils were encountered at the ground <br />surface and extended to depths of about 5 to 30 feet below existing site grade. The native <br />soils consisted predominantly of sands with varying amounts of clay, silt, gravel and <br />cobbles, and gravels with varying amounts of clay, silt, sand, and cobbles. Some layers of <br />clay with varying amounts of sand, silt and gravel were also encountered, predominantly <br />within the eastern portion of the site. Claystone and/or sandstone bedrock materials were <br />encountered beneath the native soils in the majority of the borings from the current and <br />previous study and extended to the full depth of exploration. The claystone and/or <br />sandstone bedrock materials were encountered at depths ranging from about 7 to 30 feet <br />below existing site grade. Bedrock was not encountered to the full depth of exploration in <br />two of the borings where auger refusal was encountered at depths of about 5 and 18 feet. <br />Delivering Success for Clients and Employees Since 1965 <br />More Than 70 Offices Nationwitle <br />