2015-02-17_REPORT - M1973036

• Permit No: M1977036
• IBM Index Class Name: REPORT
• Doc Date: 2/17/2015
• Doc Name: Geotechnical Stability Analysis
• From: GEI Consultants
• To: DRMS
• Email Name: PSH
• Media Type: D
• Archive: No

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January 13, 2015
GEI Project Number 140297 -1010
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DIVISION OF RECLAMATION
MINING AND SAFETY
Peter Hays
Colorado Division of Mining, Reclamation, and Safety
1313 Sherman St., Room 215
Denver, CO 80203
GEI Way)
Re: Geotechnical Stability Analysis for Martin Marietta Greeley 35" Avenue Mine, M-
1973 -036
,______,.Weld County, Colorado
Dear Mr. Hays,
This letter addresses the Geotechnical Stability Exhibit for the Martin Marietta, Inc. (MM)
Greeley 35th Avenue Mine (M- 1977 -036) Reclamation Permit amendment, per Rule 6.5.
The geotechnical stability exhibit is required in the event of unreturned Structure Agreement
letters from owners of permanent structures within 200 feet of the mine boundary.
The Greeley 35th Avenue Mine is located in northeast quarter of Section 34, the southeast
quarter of Section 35, and the north half of Section 35 of Township 6 North, Range 66 West
of the 6th Principle Meridian.
Permanent man-made structures within 200 feet of the mine boundary include: Residential
housing structures, below grade ponds, hydrological structures, concrete recreational path,
gas pipelines and associated well pads, railroad tracks and miscellaneous appurtenances,
electrical transmission lines, county owned roads, and a tennis court (see complete list of
owners and structure descriptions on page 2).
Geologic Strata and Mining Conditions
The Greeley 35th Avenue Mine is located at 925 N. 35th Avenue in Greeley, Colorado and is
adjacent to the Cache la Poudre River. Mining at the Greeley 35th Avenue Mine is ongoing
and is anticipated to be completed by December 31, 2019, depending on market conditions.
Approximately 130 acres of the western portion of the Greeley 35th Avenue known as the
"West Pit" will be mined and reclaimed simultaneously. The West Pit is intended to be lined
with a soil - bentonite cutoff wall. The cutoff wall construction will encompass the West Pit.
Other work areas of the mine will not be changed from the current approved mine permit.
Boring data gathered from a field investigation in March of 2014 included 43 borings to
investigate the subsurface soil, bedrock, and groundwater conditions within the Greeley 35th
Avenue West Pit footprint. The boreholes, in addition to observations made within the
mined pits, indicates that there is a layer of overburden above a layer of pit run (sand and
gravel), overlaying bedrock. Overburden and pit run have variable depths, depending on
locations in the mine and the mining phase. The bedrock underlying the mine is
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