2023-10-31_REVISION - M1973021 (2)

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Table 1-2. Existing Sub-basin Characteristics Summary Drainage Areaa Description Drainage Area Runoff Outfall (acres) 01A and 01B Unnamed Drainage 2 58 Off-Siteb 02 Main south quarry 52 Outfall 003, Outfall 006 03 Unnamed Drainage 1, 88 Detained in central quarry or west quarry haul road, south quarry and pumped to and the central quarry Outfall 003 or Outfall 006c 04 Eastern south quarry 10 Detained in eastern portion of south quarry and pumped to Outfall 006c 05 Strain Gulch upstream of 330 Conveyed beneath the north Site quarry and processing area in an existing 72-inch culvert 06 North quarry 80 Contained in Reservoir Site 11 07 Processing area 28 Outfall 005 08 Main quarry haul road 12 Outfall 001 09 Bottom of main quarry 1 Outfall 004 haul road below sediment basin a. As shown on Drainage Area Maps in Appendix B b. Previously included to compare with proposed conditions, no change from existing condition proposed c. Runoff will be pumped to an outfall if it has not infiltrated within 72 hours Drainage areas 01A and 01 B are for Unnamed Drainage 2 (UD2), which is partially within the property boundary but is unimpacted by quarry development. UD2 flows from west to east into Turkey Creek south of US-285. This drainage area was previously included to compare with proposed conditions; however, the Phase III design does not impact 01A and 01 B. Drainage area 02 consists of the south quarry which includes the upper highwall and benches and lower portions of the west quarry haul road. Runoff from drainage area 02 reports to Outfall 003 and Outfall 006. Outfall 003 discharges into the existing UD3 channel downstream of the Site. The downstream UD3 channel flows into Turkey Creek approximately one mile downstream of the outfall. Outfall 006 discharges to UD2 downstream of the Site. If the flow enters the south quarry depression, the accumulated runoff is allowed to infiltrate or is pumped to Outfall 003 within 72 hours. Drainage area 03 consists of Unnamed Drainage 1 (UD1)which is upstream of the Site, upper portions of the west quarry haul road, and the central quarry. The drainage area for UD1 upstream of the Site is 30 acres of undeveloped land located within the Mount Falcon Open Space Park. UD1 flows into the site between the south and central quarries and ultimately flows either down the newly constructed west quarry haul road to the eastern portion of the south quarry or into the depression created by the south quarry. If the flow enters the south quarry 1670 Broadway,Suite 3400,Denver,CO 80202-4824 hdrinc.com (303)764-1520