PERMFILE50679

• Permit No: C1980004A
• IBM Index Class Name: Permit File
• Doc Date: 5/13/2002
• Section_Exhibit Name: APPENDICES K - P
• Media Type: D
• Archive: Yes

APPENDIX M (cunt)
• SMALL AREA EXEMPTION # 1 - SAE-1
OFFICE RELOCATION: SURFACE WATER CONTROLS
When the offices were moved to McClave the disturbance was about
19,000 sgft. An additional 14,600 sgft of undisturbed area will drain
into the surtace water controls. The following calculations will document
that the surtace water runoff will be properly handled. There will be no
sediment pond for this small area. Rather, a small sediment trap with a
boom to collect oil will be installed at the lower end of the parking area.
SPECIFICATIONS
Disturbed area = 19,000 sgft 0.44 acres Ave. Slope = 5
Natural area = 14,600 sgft 0.34 acres Soil ~ Glendive
Total area = 33,600 sgft 0.77 acres Group = B
Length = 200 ft Veg. cover = 70 °k
PEAK FLOW CALCULATIONS
1. From "Peak Flows In Colorado" P10 = 1.7" P25 = 2.1"
2. Runoff: CN disturbed = 98 CN natural = 42 use 50 (sage/grass)
• Weighted Average CN = {(50'14.6)+(98'19.0)}/(14.6+19.0) = 77
RUNOFF Pe 10 = 0.30 inches Pe 25 = 0.50 inches
3. For Area = 1 acre & Slope = 5°~ Slope Adj. Factor = 1.0
4. For Hydraulic Length = 200 ft Equivalent Area = 0.93
5. For CN = 77 and Area = 1 ac ; Peak Discharge is about 2 cfslnch
6. Equivalent discharge q10 = 0.60 cfs
q25 = 2`0.39"'1.04 = 0.81 cf: q25 = 1.00 cfs
7. The ACTUAL DISCHARGE is '010 = q10 ' A / Ae = 0.50 cfs
025 = 1.00' 0.77 / 0.93 0.83 cfs
8. VOLUME DISCHARGED is: X yr runoff' A/12 = 0.3"' 33,600/12
V10 = 840 cuff
V25 = 1400 tuft
SIZE OF THE SEDIMENT TRAP
Length = 20 ft Width = 20 Ft Depth below grade = 3.5 ft
The VOLUME of the trap will be 1400 CUBIC FEET.
Mc Vol III PAGE M - 2 10-13-91