APPCOR11307

• Permit No: C1981015
• IBM Index Class Name: Application Correspondence
• Doc Date: 4/2/1981
• Doc Name: DORCHESTER COAL CO FRUITA MINE PERMIT APPLICATION SEDIMENT RUNOFF CONTROL FN C-015-81
• From: MLR
• To: BRIAN MUNSON
• Media Type: D
• Archive: No

1 STATE OF COLORADO RiCNA~.I~Cnv crn or
DEPARTMENT OF NATURAL RESOURCES
D. Monte Pascoe, Executive Director
iii iiiiiiiiuiiiiii
999
MINED LAND RECLAMATION
423 Centennial Building, 1313 Sherman Stree[
Denver, Colorado 80203 Tel. [phone]
David C. Shelton
Director
April 2, 1981
TO: Brian Munson
FROM: Richard Domingue ~ ~~n,
RE: Dorchester Coal Company - Fruita Mine Permit Application
Sediment/Runoff Control - Our File Number C-015-8I
1. Ditch Designs: The parameters needed to determine the peak flow using
the SCS method referenced in the permit application are not given in the
application. Dorchester Coal Company (DCC) must:
A. submit copies of the calculations used to estimate peak flows for each
of the ditches including:
i. contributing areas,
ii, curve numbers, and
iii. surface slope.
B. provide a map which delineates the watershed areas contributing to the
upslope diversions (perimeter ditches).
2. Diversion Ditch Designs: Ditch designs for the western portion of the
perimeter diversion and collection system are not given in the recent application.
DCC must present design dimensions for the entire perimeter/diversion ditch
system. Design dimensions for the section of the perimeter diversion labeled
D to E are incomplete. DCC must submit the top width dimension in order to
completely define the geometry of the channel.
3. Ditch Velocities: Actual ditch velocities in the diversion/collection
system are very high and erosive. DCC claims these channels are not erodible
and conversations with personnel who have inspected the site confirm this.
However, areas of erodible soils are crossed in some parts of the system
especially near the sediment ponds. Protection measures taken at these sites
must be detailed in order to estimate their effectiveness in controlling erosion.
4. Sediment Ponds: DCC must provide a detailed drawing of Pond No. 1 as no
drawing of this structure is provided.
5, Sediment Pond No. 2 Design: While the inflow estimated by DCC is very
conservative and the design storm return period exceeds our requirements the
method used to justify the primary/emergency spillway design is inappropirate or
incomplete. LCC uses the Manning's Equation; This method has several drawbacks
which make it inappropriate for spillway design; it is meant to be used in
open channels and it does not estimate the head necessary to develop the flow.
(cont'd)