REV00083

• Permit No: C1981071
• IBM Index Class Name: Revision
• Doc Date: 9/1/1993
• Doc Name: SEDIMENT YIELD DEMONSTRATION BLOCK C
• Type & Sequence: SL3
• Media Type: D
• Archive: No

Sep ember 1993 CYVCC - Sedimen7 Yield Demourration - Block C ~ I
1.0 INTRODUCTION
Cyprus Colorado Yampa Coal Company (CYCC) is in the process of requesting a Phase II and
Phase III bond release for Block C which is located in the Colorado Yampa Coal -Eckman Pazk
Mine permit area approximately 25 miles west of Steamboat Springs, Colorado. As part of the
request, CYVCC contracted TerraMatrix Inc. (formally ACZ Inc.) to conduct a sediment yield
demonstration for Block C.
Block C consists of 4 sepazate areas as shown on the Block C Bond Release Map. For this report
the areas aze labeled 1 through 4. The size of each area and date of seeding aze as follows:
AREA SIZE DATE SEEDED
1 95.1 acres 10/80, 10/81, 8/82, 10/82
2 39.3 acres ~ 12/81, 8/82
3 30.2 acres 12/81
4 8.1 acres 10/80
According to Division of Minerals and Geology (DMG) regulation 3.01(3)(b), no more than 60
percent of the bond can be released until the applicant demonstrates that existing conditions will
result in equivalent or lesser sediment contributions to surface runoff when compared with pre-
disturbance conditions or undisturbed areas.
CYCC was granted a change in postmining land use from rangeland to pasture by DMG for the
area containing Block C. The premining vegetation cover type of rangeland (oak-aspen) vazy
significantly from the vegetation cover type for the approved postmining use of pastureland
(herbaceous). Due to the significant differences between these two vegetation cover types it would
be difficult to develop a direct sediment yield compazison to satisfy DMG regulation 3.01(3)(b).
Given the change in postmine land use, TerraMatrix developed a model to compare the runoff
from Block C to adjacent pasturelands.
To demonstrate that runoff from Block C will result in equivalent or lesser sediment contributions
to surface runoff when compared with adjacent pastureland conditions, TerraMatrix has developed
a site drainage and sedimentology model utilizing SEDCAD+. SEDCAD+ is a computer
softwaze program developed to assist in the evaluation of stormwater runoff, erosion, and
sediment control management techniques.
To developed an accurate model for the existing condition of Block C, TerraMatrix utilized the
1992 Block C vegetation survey conducted by CYCC and soil information from the existing
permit document as input to the SEDCAD+ program.
Tu develop a model for an adjacent pastureland area which would be comparable to Block C,
TerraMatrix utilized the 1992 pastureland reference area vegetation survey conducted by CYVCC.
The pastureland reference azea has been established as being representative of the vegetation found
TERRAMATRIX • P.O. Bor 774018 • Sleamboaf Springs, Colorado 80477 •[phone]