2011-06-21_APPLICATION CORRESPONDENCE - C2010088

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Corey Neaps CAM Colorado LLC .Tune 21, 2011 Page 37 design and location of these ponds meet the Union Pacific railroad's requirements governing the construction of embankments? CAM : No longer applicable. The railspur could be considered as a haul road not in the disturbed area as defined in Rule 4.05.2(4) and, therefore, falls under Rule 4.03.1(4)(iv), best management practices will apply. Please see revised sediment pond configuration as shown on Map -16. Division Response: Response accepted regarding the reconfigured sediment pond designs. However, there are still questions regarding the entire rail loop being considered as not in the disturbed area (see Item 47 above). 55. Under Rule 2.05.3(4), in the Sedcad designs, CAM is using 1.4 inches, 1.8 inches and 2.2 inches as the design precipitation events for the 10 yr 24 hour event, 25 year 24 hour event and 100 year 24 hour event respectively. However, referring to the NOAA Atlas 2 "Precipitation- Frequency Atlas of the Western United States ", the Division obtained values of 1.6 inches, 2.0 inches and 2.6 inches respectively. It appears that CAM may have used the NOAA May to October precipitation event figures rather than the NOAA annual precipitation event figures. Please justify the precipitation event values used in the Sedcad designs or revise the Sedcad designs accordingly. CAM Response: Precipitation values have been revised. Please see revised Exhibit 9. Division Response: Response accepted. 56. Under Rule 2.05.3(4), in the Sedcad designs for the west culverts, a curve number of zero is used for the irrigated wetlands area, citing a ground cover of 100% as justification for that curve number. If the wetlands are saturated or are comprised of standing water, a precipitation event could produce runoff, in spite of the vegetative cover. Please describe the nature of the wetlands as it relates to the determination of the curve number. CAM Response: Revised the Curve Number to 74, based on cover of 97.33 %, which equates to "Good ", for a soil type of `C': Please see revised page Exhibit 9 -49. Division Response: In the submittal dated April 11, 2011, CAM revised the curve number of the wetlands to 74, which is a reasonable value to the Division. However, the April 11, 2011 submittal left out the Sedcad peak discharge data sheet for the west culverts that had been included in the original submittal on page Exh -9 -7. In addition, there are no Sedcad data sheets that show the peak discharge for the designed event for the other culverts on site. Finally, there are no Sedcad designs that show that a culvert of a certain diameter can handle the designed peak discharge for the designed precipitation event. Please provide the appropriate Sedcad data sheets for all of the loadout culverts.