2017-11-29_REVISION - C1981038 - Laserfiche WebLink

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November 15, 2017 Mark Schaffer, President North Fork Farmers Ditch Association P.O. Box 1536 Paonia, CO 81428 Re: Inspection and Rating of 600-ft Long Culvert at Bowie Resources, Parcel No. 318729400067 Mr. Schaffer: At the request of Erich Niermann, we performed an inspection of the subject culvert to determine a remaining serviceable lifespan based on the current condition of the pipe. The culvert is over 600 feet long and five feet in diameter. It traverses under the old Bowie Mine spur takeoff area and under an adjacent detention area. Much of the culvert is under a detention area on the north side of the old Bowie Resources spur load-out area and a portion of it is under the old load-out roadways and therefore subject to truck loads at the western end (see attached aerial map of the culvert in Exhibit A). This letter is intended to summarize our findings and present the results of a rating analysis, and to estimate a remaining serviceable lifespan. Summary of Inspection The culvert itself is five feet in diameter, 12-gage annular corrugated, galvanized steel. It is bolted together in pieces and at the joints between sections using 7/16” bolts. Beginning at the western end, the culvert appears to be in very good shape for an approximate age of 40 years. There is no apron present at the western end and no sign of major erosion, which is expected at the exit end of a culvert. The culvert itself is in very good condition for approximately 150 feet from the western end and shows no signs of settling or excessive corrosion. Two small holes were drilled through the bottom of the pipe approximately 100 feet from the western end to determine the thickness of the remaining metal. We estimate about 80% of the thickness remains. Water marks from the full-flowing ditch are at approximately 50% of the culvert depth. (See various images of the interior of the culvert at the end of this letter in Exhibit A) Between 150 feet and 200 feet from the western end of the culvert, standing water and sediment is present. Within 100 more feet, the depth of water is approximately 9-12 inches and failure from deterioration of the culvert wall is visible along the northern side within a five-foot section. Around this location, damage to the top of the culvert is present, likely from rocky backfill material that punched into the culvert as the fill was compacted. At the location of most extreme deformation, the height of the culvert was measured to be four feet (20% vertical deflection) and the width of the culvert had increased by four inches (approximately 7%). Markings from the ditch water deepened in this area to approximately 80% of the depth of the culvert due to a sunken invert. Seams and joints between pipe lengths are separating in the areas of highest deterioration and surrounding soil is present through perforations, indicating water infiltration and erosion around the pipe is possibly