GENERAL49395

• Permit No: M1977436
• IBM Index Class Name: General Documents
• Doc Name: TERMPORARY SUPPLY PLAN
• Media Type: D
• Archive: No

• i
at the pits are 10,000 gpm, approximately 14.4 hours per day (60% ofthe 24-hr day), seven days per
week.
The boundary conditions chosen for the model were for Aquifer Option 2, which is an alluvial aquifer
bounded by a stream and a parallel impermeable boundary. Input to the model includes a well
pumping rate, the transmissivity of the aquifer, the specific yield, the distance between the well and
the South Platte River, the distance between the river and the parallel impermeable boundary (a steep
ridge to the southeast), and incremental time periods. The values selected for each variable are:
Well Pumping Rate - 10,000 gpm
Transmissivity - 100,000 gpd/ft (chosen as a representative well potential of "good to very
good" for irrigation)
Specific Yield - 0.18 (selected for the specific yield for moderately wet alluvial lands in
Adams County, from the Soil Survey of Adams County Colorado (SCS))
Distance between well and So. Platte River (x) - 100 ft.
Distance between the river and the parallel impermeable boundary -average of 2400 ft.
Results can be reviewed in Attachment 2.
Product Losses
Wet screening of the product uses 800 gpm per day, five days per week. Approximately 4% of the
amount of water (30 gpm/]0 hrs or 12.5 gpm/24 hrs) used for wet screening will go out on the
product. Table 2 shows the volume of stream depletion of water pumped for wet sieving,
Historic Consum~ve Use
The consumptive use by vegetative growth was determined for alfalfa using the Blaney-Griddle
formula. A consumptive use credit was then applied against groundwater depletions by the well and
wet sieve processing of the product. A Historic Consumptive Use credit was determined for alfalfa,
the primary pre-mining agricultural use of the area. The Blaney-Griddle formula estimates monthly
ET, and was used to determine consumptive use (evapotranspiration). This calculation is shown in
the following equation.
U = (k*t*p)/100, where:
U =consumptive use
k =consumptive use coefficient, crop specific. For alfalfa, the range of k values for the
average 184 day planting season of alfalfa is 0.56 to 1.05.
t =mean daily temperature in degrees Fahrenheit. Ranges from 51.1 to 72.8 during the
growing season.
p = percentage ofdaylight hours for the growing season; this value ranges from 1.87 to 10.20.
The resulting estimate of monthly consumptive use by alfalfa grown near Denver, Colorado, shown
in Table3, was taken from Sample Calculation 2A-2 in the National Engineering Handbook Part 623,
Irrigation Water Requirements. This calculation shows historic consumptive use ranging from 1.66