2019-08-21_REVISION - M1976056 (6)

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McAtee Construction Company Page 4 Riverside Pit-M-1976-056 August 20,2019 A copy of the 2007CW0300 case is attached. We have requested a copy of 2017CW0362 from the Logan Well Users Association ( LWUA)and have had no luck getting a copy from them. I went on the Division 1 Water Court records and retrieved the April 2017 Water Resume Publication that shows the LWUA application. I have proved the sections that discuss this case and highlighted the area pertaining to McAtee Construction Company for your review. 9. On Page 15, the Applicant states minor revisions may be necessary to the permit since they are increasing the amount of lake areas when mining is complete. Please commit to revising the augmentation agreements prior to exposing more than the currently approved groundwater exposure amount. McAtee Construction Company will work with the Logan Well Users Association to revise the augmentation plan and well permit prior to exposing more water then currently approved in Cases #2007CW0300 and #2017CW3062. In 17CW3062 McAtee will be able to expose approximately 43.20 acres more than the pre 1981 lake surface area of 5.7 acre for a total of 48.90 acres total. At this time there is approximately 22.67 acres total lake area at the mine. 10. The site was significantly affected by a flood event in 2013 which altered Lake Robert and deposited material in the southeast section of the East Lake area adjacent to the Lowline Ditch. It appears the mine site is within the 100-year floodplain of the South Platte River. In the event of a significant flood event(100-year flood) it is likely the mine site would be captured by the Lowline Ditch and/or the South Platte River. Where mining will occur within 400 feet of the river channel, a flood analysis and flood control plan must be evaluated and submitted for Division review and acceptance. The flood analysis should quantify the velocity and volume of flows expected on site from a 100-year flood event, as well as the elevation of the 100-year base flood event and its relation to the elevation of any proposed spillways and embankments. The flood control plan should address mitigation measures including pit side armoring, river side armoring, inflow and outflow channels, or other appropriate measures. The Applicant shall provide the flood elevations to be expected under a"worst case" flooding scenario and specific mitigation measures to be implemented to minimize the potential for any offsite impacts. Riverside berms are proposed in the Riverside Pit amendment application, which may be prone to erosion during a flood event. The potential for"berms"around gravel pits to be damaged during flooding is discussed in detail in the 1987 Urban Drainage and Flood Control District(UDFCD) Publication "Technical Review Guidelines for Gravel Mining Activities within or Adjacent to 100-year Floodplains." Strips of native ground or constructed fill between the stream and the gravel pit, and generally aligned with the flow direction of the river are referred to in the UDFCD document as Riverside berms.