GENERAL46203

• Permit No: C1981028
• IBM Index Class Name: General Documents
• Doc Date: 10/8/1981
• Doc Name: Draft Copy of Revised Decision Documents
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

some unique opera tinq and r'r•cl.unntion ~~i~:taclr^:.
The operator conducted an extrn,ive dr.iiliny Program (gin characterize_ the physical
and chemical properties of the overLurden.
The information on physical and chemical characteristics can be found in Appendix
L-1, G-1, and H-1 of the application. The applicant adequately considered
the overburden characteristics on the backfilling and grading operations and
the zevegetation plan (see Appendix L-1, Q-1, and pages 35, 36, and 37 of
Volume 1 of the application). In addition, the applicant considered the over-
burden chemical characteristics on the potential for ground water quality
degradation. R discussion of these affects fan be found in Appendix I-1 of
the application.
Based on the information supplied in the application, the Division finds that
the applicant has complied with the requirements of section 2.04.5 and 2.04.6.
V. Hydrologic Balance: Surface Water (2.09.5, 2.04.7, 2.05.3, 4.05)
The operation 1s located in the South Platte River Da sin in Weld County.
There are many important streams Located within f9e1d county including the Cache
La Poudre River, Vrain Creek, Crow Creek, and l:iowa Creek, all of which flow
into the South Platte River. however, these streams arc distant from the mini
site and could not. be affected by the operation. Two potential streams arc
. Zocated adjacent to the mine area. Box E1 der Creek, an intermittent stream,
is located to the west of the mine plan area. 1'he watershed of this stream is
located outside the mine p]an area and the ground water within thr_ five-year
mine plan is not hydraulically connected to this stream. Because of this, the
.Division has excluded -ox Elder Creek from further consideration in this permit.
Surface water runoff from the mine plan area would flow to the cast to Ennis
Draw. Historically, this draw has shown no evidence of surface water f1 ow.
Because the draw is covered by blowsanrl, all flow in this draw is subsurface
and can be considered to be an unconfined ayui.fer. Therefore, impacts to
Ennis Draw were considered under the Ground Water discussion.
The applicant has submitted a study on the rst'imate of runoff expected from the
mine permit area (see pages 46-50 of the appli.cati,on). The es tim~ting procedure
used is outlined in section 4, hydroloyu of the ha tional Engineering Handbook,
U.S.D.A., SCS, 1968. Precipitation data used was from Technical Paper IJO. 40,
U.S. Department of Commerce, 1961 and was verified by the Division using NOAH
precipitation data. Curve numbers considered were found to be justified for
the site. The results of the study showed that for a "good hydrologic" condition
no runoff would be generated from a 10-year 24-hour event. This prediction seems
reasonable based on the fact that on-site inspections of the mine by the operator
and N,LRD staff showgirl no signs of visible runoff nor aril defined runoff channels.
The reason for the .lack of rwroff is the highly permeable mantle of sand that
overlies the mine plan area.
Theapplicant also considered the runoff es tirrurted from the mine area under
"fair hydrologid"conditions. T1ris condition may exist in areas that are
compacted with no vegetative cover, such as haul roads: The results of the
study showed a runoff depth of 0.07 inches or 9.8 acre-feet for the 1675 acre mine
plan area. Since runoff could occur in areas o: "poor" or "fair hydrologic"
condition the applicant has constructed or proposes to construct four sedimentation
ponds on the east edge of the permit area. Pond volumes have been designed to