PERMFILE42781

• Permit No: M2001035
• IBM Index Class Name: Permit File
• Doc Date: 6/30/2001
• Doc Name: ROCK CUT SLOPE STABILITY ASSESSMENT PLANNED ROCK QUARRY TROUT CREEK VALLEY CHAFFEE CNTY COLO JOB 559
• From: R J IRISH CONSULTING ENGINEERING GEOLOGIST INC
• To: ACA PRODUCTS INC
• Media Type: D
• Archive: No

Y
7101 West Yale •
Avenue, No. 601
Denver, Colorado 80227
303-986-6658
R. J. Irish
Consulting Engineering
Geologist, Inc.
June 30, 2001
ACA PRODUCTS, INC.
P. O. Box 1887
Buena Vista, CO 81211
Attn.: Tim Krocesky
Project Manager
III IIIIIIIIIIIIIlII
999

Re: Rock Cut Slope Stability Assessment, Planned Rock Quarry, Trout Creek Valley, Chaffee
County, Colorado.
Job No. 559
Gentlemen:
In response to a call from your Mr. Tim Krocesky, we have geologically reconnoitered the
site ACA Products, Inc. (ACA) proposes to develop as a quarry to produce rip-rap sized rock.
Our objective has been to outline the structural and petrologic character of the bedrock at this
site, assess the probable significance of those conditions to quarry cut-slope stability, and to
suggest a cut slope configuration that we anticipate will be stable for many years after the
quarrying is completed. The quarrying is to be accomplished by drill-and-blast methods.
The quarry site occupies the terminations of 2steep-sloped, rock-faced, west-trending
ridges separated by a narrow ravine on the eastern side of the Trout Creek Valley at its
confluence with the Arkansas River Valley about 3 miles southeast of the town of Buena Vista,
in Chaffee County, Colorado, as shown on Figures 1 and 2 (prepared by ACA). This site is in
the east-central sector of the SW1/4 NW1/4 Sec. 26, T. 14 S., R. 78 W. The planned quarry is
expected to incorporate an irregularly shaped area about 1000 feet long and ranging from about
275 feet to about 550 feet wide. Maximum back-wall cut slope height is expected to be about
160 feet. The northwestern corner of the quarry is to be about 150 feet southeast of the
downstream toe of the Trout Creek Dam, aroller-compacted concrete structure constructed last
year.
During the course of our work we have reviewed our report on our engineering geologic site
investigation for the neighboring Trout Creek Dam, reviewed published geologic maps pertinent
to the quarry site, geologically reconnoitered the site (on June 29, 2001), and stereoscopically
studied aerial photographs of the site and vicinity.
Site Geologic Conditions
Trout Creek drains a sector of the eastern slope of the Arkansas River Valley. That valley
topographically evidences the structural extension of the Rio Grande Rift, a large graben
structure that extends northward from Mexico through West Texas, New Mexico and central
Colorado past the towns of Buena Vista and Leadville almost to the Wyoming Border. The site
for the planned quarry lies structurally on the eastern flank of the Sawatch Uplift east of the
graben breach of that flank. Bedrock at the planned quarry site is a Precambrian-age (about 1.5
billion years ago) granodiorite, a member of the granite family of igneous intrusive rocks. At the
Consultant to Designers, Contractors, Planners