2019-08-29_REPORT - M1974086

• Permit No: M1974086
• IBM Index Class Name: REPORT
• Doc Date: 8/29/2019
• Doc Name: Geotechnical Stability Report 2019
• From: Asphalt Paving Company
• To: DRMS
• Annual Report Year: 2019
• Email Name: ECS
• Email Name: MAC
• Media Type: D
• Archive: No

BRIERLEY
ASSOCIATES
Creating Space Underground
August 29, 2019
File No.: 514104-001
Asphalt Paving Co.
14802 W 44th Ave
Golden, CO 80403
Attention: Stan Opperman
Subject: Geotechnical Stability Report
Ralston Quarry
Golden, Colorado
Brierley Associates (Brierley) has conducted a geotechnical stability evaluation on August 23,
2019 for the Asphalt Paving Co. (APC's) rock quarry located at 6569 Highway 93, just west of
the intersection with West 64th Parkway, in Golden, Colorado. Brierley has previously produced
a Geotechnical Evaluation and Initial Opinion Report— Phase 1, dated August 2011, a
Geotechnical Evaluation Report- Phase II, dated November 2013, and an Additional Slope
Evaluation letter, dated July 2014 for the same site.
Based on discussions with APC and Greg Lewicki and Associates, PLLC, Brierley understands
that the Division of Reclamation, Mining and Safety(DRMS) has added a geotechnical stability
report as part of the annual reporting. This letter presents the results of this evaluation. The
extent of this evaluation was limited to the basalt quarry and does not include any peripheral
areas.
1.1 Existing Conditions
1) Provide an accurate description of the existing high-wall material(s), geotechnical
characteristics, bench, and wall configuration.
According to bedrock geologic maps of the area, the quarry is operating within the western half
of the Ralston Dike, or Ralston Plug. Lava was extruded through the Pierre Shale from the
Ralston Plug during Paleocene time. An altered zone of the Pierre Shale is adjacent to the
Ralston Plug. The contact between that Pierre Shale and the rim-phase of the Ralston Plug is
mapped within the quarry as dipping from 60 to 80 degrees to the east(Drewes, 2006). The
core-phase of basalt is towards the center of the Ralston Plug.
In general, a thin veneer of basalt overlaying the east-dipping shale contact was left in place on
the west side during mine operations. A few"windows" of the altered Pierre shale have been
exposed in the upper high walls and appear to be standing well where exposed. Based on 2010
mapping, and subsequently reviewed, the rim-phase basalt is very hard, fresh, gray, and very
fine grained, with joint orientation ranging from moderately dipping to vertical. The core-phase
basalt was hard, moderately weathered to fresh at depth, light gray, and very fine grained, with
joint orientation ranging from low angle to high angle.
990 S. Broadway,Ste.222, Denver,CO 80209 1303.703.1405 1 www.BrierleyAssociates.com