2008-04-15_REVISION - M1980244 ‎(325)‎

• Permit No: M1980244
• IBM Index Class Name: REVISION
• Doc Date: 4/15/2008
• Doc Name: VOL II Appendix 2, Hydrologic Evaluation Report
• From: CC & V
• To: DRMS
• Type & Sequence: AM9
• Media Type: D
• Archive: No

Grassy Valley hydrologic conditions 31
is assumed that any water infiltrating the low permeability cover will flow through
the ECOSA and drain towards the main diatreme.
• Water draining from the regraded areas upgradient of the ECOSA will flow to
Grassy Creek (near GV-02), or will flow towards the backfilled WHEX portion of
the East Cresson Mine and will infiltrate the backfill and drain towards the main
diatreme.
4.4.5 /nput data
Simulation settings
The GoldSim water balance model was run for one year using daily time steps. Monthly
average values for precipitation, evaporation and ET are used in the model. Using a daily
time step with monthly input data improves model accuracy by reducing the magnitude of
parameter value changes between time steps.
Precipitation
Average monthly precipitation data are reported in Table 2.3. These monthly values and the
annual average precipitation also are shown in Table 4.2. Some precipitation falls as snow
during the winter months. Average snowfall data for Victor, CO (Section 2.0) was used to
estimate snowfall for Grassy Valley. Asnow-water-equivalent of 11 percent was selected
such that the estimated snowfall contained a similar amount of water to the average monthly
' precipitation. It was necessary to adjust the snowfall data slightly to give the appropriate
amount of precipitation during each month. Water stored as snow is released to the
drainage during the'spring. There are no data available for the snow melt rate in Grassy
Valley, therefore this rate was used as a calibration ,parameter. Table 4.2 presents estimated
snow fall rates and snow melt rates, together with monthly precipitation rates.
Table 4.2 Monthly precipitation and snow data used in water balance model
Average monthly Average monthly Average monthly Snow-water- Snow melt
Precipitation* rainfall snowfall equivalent (inches
_ (in) (in) (in) (in) of water)
Jan 0.6 0.0 5.7 0.6 0.0
Feb 0.6 0.0 5.0 0.6 0.0
Mar 1.3 0.0 12.0 1.3 0.0
Apr 1.4 0.0 12.6 1.4 2.0
May 1.6 1.3 3.3 0.4 2.0
Jun 1.8 1.8 0.1 0.0 2.6
Jul 4.3 4.3 0.0 0.0 0.0
Aug 3.5 3.5 0.0 0.0 0.0
Sep 1.5 1.4 1.3 0.1 0.0
Oct 1.1 0.0 10.0 1.1 0.0
Nov 0.6 0.0 5.5 0.6 0.0
Dec 0.5 0.0 4.6 0.5 0.0
Total 18.9 12.3 60.1 6.6 6.6
"Smith Williams Consultants, Inc, March 2008.
Evaporation/ Evapotranspiration
2736 Cripple Creek & Victor Gotd Mining Company
Water Management Consultants