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Memo <br />ENGINEERING SURVEYING INC <br />Goff Engineering & Surveying, Inc. <br />126 Rock Point Drive Suite A • PO Box 97 Durango, CO 81302 <br />www.Roffenfineering.com (970) 247 -1705 (voice) (970) 247 -1710 (fax) <br />Project: Carbon Junction Mine <br />Re: Segment 4 Culvert — As -built capacity <br />Date: May 7, 2007 9) <br />To: M. Savage From: B. Duff I R. Markgraff ledlWL <br />On 6 April, 2007, Bryan Duff and I conducted a field examination of the culvert system currently <br />installed under the main access road. The main purpose of this culvert crossing is for the diverting the <br />Carbon Junction canyon run -off under the existing road system and into it's historic drainage course. This <br />system is identified as Segment 4 and is discussed in Section 205 (pages 5 -9 and 5 -14) of the Carbon <br />Junction Mine Abridged Permit Document Text CDMG # C-92 -080. While at the site, we observed the <br />following: <br />The culvert system consists of 2 circular Corrugated Metal Pipes installed in a parallel configuration <br />through (under) the roadway embankment. Each culvert measures approximately 90 feet in length and <br />has a diameter of 66 inches. The centerlines are approximately 9 feet apart, and the pipe terminations are <br />square-cut and protrude into the channel areas on both ends. <br />Using an optical level, the elevation difference was measured between the entrance and exit inverts to be <br />approximately 14.3 feet. Also measured was the spill -over point elevation difference into the ditch (along <br />the roadway) at approximately 5.9 feet above the entrance inverts, with the roadway crown at 6.3 feet <br />above the entrance inverts. The culverts were observed to be clear throughout without any noticeable <br />deformation. <br />Based on the condition and orientation of the culvert system, the Culvert Calculator software module <br />(within Land Desktop V2007) was used to calculate its flow capacity. This capacity (referred to as As- <br />Constructed amount) was calculated to be approximately 345 CFS at the point where the headwater <br />reaches the lowest point of the drainage swale adjacent to the roadway crown. A review of this calculated <br />discharge with the calculation in the Permit Document was completed. This review showed the <br />calculated amount in the Permit Document to be approximately 346 CFS. As can be observed, it appears <br />that the `As- Constructed' amount is the same amount as the calculated amount given in the Permit <br />Document. <br />Attached is a copy of the output report for your files. <br />