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June 27. 2006 <br />Carma <br />Highland Place 11 <br />9110 East Nichols Avenue, Suite 180 <br />Greenwood Village, Colorado 80112 <br />Attn: Mr. Tyler Packard <br />1 ~~rracon <br />Consulting Engineers 8 Scientists <br />70625 West 1-70 Frontage Road North, Suite 3 <br />Wheat Ridge, Colorado 80033 <br />Phone 303.423.3300 <br />Fax 303.423.3353 <br />www.terracon.com <br />Re: Clarification of Recommendations for Lake Embankment Slope Protection <br />Proposed St. Vrain/Bayshore Development <br />Carma Weld County Site <br />Weld County Road 28 and Weld County Road 9-1/2 <br />Terracon Project No. 25045300 <br />Siegrist Construction Company M-1982-015 <br />At your request, Terracon is providing clarification/detail of the slope protection <br />recommendations provided in a letter prepared on June 2, 2006, ("Global Slope Stability <br />Analysis For Embankment/Slurry Wall Construction and Impact Assessment for Existing <br />Manmade Structures"). The purpose of the clarification is to provide additional detail of the <br />proposed rip rap placement along the southern edge of the lake embankment and to <br />address concerns outlined by the Colorado Division of Minerals and Geology (DMG) in a <br />meeting held on June 22, 2006. <br />In the previously referenced letter, it was recommended that: <br />"...the St Vrain River side of the lake embankment will require a face <br />protection consisting of 12" diameter rip rap extending from the toe of the <br />slope to the crest of the slope. Furthermore, the slope should be <br />constructed to a maximum slope inclination of 2-1/2 to 1 (Horizontal: <br />Vertical) in order to provide a stable configuration for rip rap placement and <br />overall global stability... Furthermore, flattening of the existing slope to a <br />maximum inclination of about 2-1/2 to 1 will be required. It is our <br />recommendation that anon-woven geotextile filter fabric with sufficient <br />weight/strength to withstand rip rap placement be installed behind the rip rap <br />erosion protection to provide confinement of the underlying soils and prevent <br />loss of fine materials migrating through the rip rap during precipitation/runoff <br />events." <br />Based on comments from the DMG at the June 22, 2006 meeting, we understand that there <br />are the following concerns concerning the rip rap placement along southern lake <br />embankment edge and the global stability analyses: <br />Delivering Success for Clients and Employees Since 1965 <br />More Than 80 Offices Nationwide <br />