2024-06-28_PERMIT FILE - M2024034 ‎(5)‎

• Permit No: M2024034
• IBM Index Class Name: Permit File
• Doc Date: 6/28/2024
• Doc Name: Application
• From: Asphalt Specialties Co., Inc
• To: DRMS
• Email Name: NCG
• Email Name: JLE
• Email Name: EL1
• Media Type: D
• Archive: No

6.1.3. Flood Protection
Mining will extend to within 200 feet from the South Platte River as shown on the Drainage Map.
Due to this proximity to the river, measures will be taken to protect the riverbank from erosion
during a flood event. An inflow and outflow structure will be constructed between the River and
the mining pod once mining is within 300 feet of the river. These structures will allow for the
safe exchange of flood waters between the pit and river which prevents erosion of the riverbank
and pitside slope during flood events. These structures are of a design approved for use by the
Mile High Flood District. Details of the inflow/outflow structure are shown on Map F-2.
6.2. Disturbed Area Runoff
During all stages of mining, there is enough water storage capacity to contain the 5-year and
100-year 24-hour storm events and prevent erosion from surface water discharge. The
expected rainfall from these events at the Marcovich Site is provided in Table G-2 below.
Table G-2. Area Storm Events (from NOAA2)
Event Probability Event Rainfall
(inches)
5-YR 24-HR 2.29
100-YR 24-HR 4.64
The peak runoff was generated from these values for the three drainage basins during all
stages of mining. Pre-mine, mining, and reclamation conditions are delineated on the Drainage
Map. The discharge volumes from these storm events are calculated in Appendix G-1 at the end
of this exhibit. Table G-3 summarizes the runoff volumes and storage volumes for each
drainage. All drainage calculations were made using the Rational Method identified in the Mile
High Flood Control District.
Table G-3. Drainage Calculations
Drainage Basin 1
Site 100-Yr 24-Hr Discharge Detention Capacity
Condition Area(ac) Curve Number Runoff(ac ft) Flow Rate (ac ft)***
(gpmr
Base 44.0 70 6.55 0 N/A
-----
Mine 44.0 44.0 82 10.3 1000-3000** 820
Reclamation 44.0 89 12.8 0 81.6
*The discharge flow rate is calculated from the peak discharge of the 100-Yr 24-Hr storm event.
**Discharge flow rate is variable and controlled during mining as all discharges are pumped from the pit
***Detention Capacity calculated in CAD as the surface volume above the pit floor(approx.25 feet @ 32
acres)or water storage pond(approx.3 feet @ 27 acres).
2 National Oceanic and Atmospheric Administration
Marcovich Gravel Pit
May 2024 G-4 Lewicki&Associates