2009-11-04_REVISION - M1983176

• Permit No: M1983176
• IBM Index Class Name: REVISION
• Doc Date: 11/4/2009
• Doc Name: Adequacy Review #1
• From: DRMS
• To: Asphalt Specialties Co., Inc.
• Type & Sequence: AM4
• Email Name: DB2
• Media Type: D
• Archive: No

ST A T E OF CO L O RA DO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203 C O L O R A D O
Phone: [phone] D I V I S c o N O F
RECLAMATION
FAX: [phone] MINING

SAFETY

Bill Ritter, Jr.
Governor
Harris D. Sherman
DATE: October 2, 2009 Executive Director
Ronald W. Cattany

TO: David Bird Division Director
Natural Resource Trustee
FROM: Allen Sorenson
RE: Review of Proposed Perimeter Drain, Asphalt Specialties Company, Inc.,
Speer Pit, Amendment AM-04, Permit No. M-1983-176
The Division of Reclamation, Mining, and Safety engineering staff (DRMS) has completed a review of the
design for the proposed perimeter drain at the Speer Pit. The drain is intended to prevent mounding of
ground water east of the pit that has been caused by backfilling the mined void with relatively low
permeability soil and inert debris. The proposed perimeter drain, if constructed in accordance with the plans
provided, will be effective in controlling the water table along the east side of the pit to an elevation of 5012
feet or less. DRMS completed a conservative analysis of the carrying capacity of the proposed drain
compared to the flow of ground water east of the pit. Ground water flow was calculated using the following
inputs taken from information in the permit file or conservatively estimated.
1. Shale bedrock is at the bottom of the excavated pit at an elevation of 4995 feet and forms a hydraulic
boundary for ground water flow.
2. Prior to mining, ground water flowed east to west through the pit area with a saturated thickness in
the alluvial sand and gravel of twenty feet or less.
3. The perimeter drain length is 3200 feet running generally south to north.
4. The hydraulic conductivity of the alluvium east of the proposed drain is less than 5 x 10-4 cm/sec, or
1.64 x 10-5 ft/sec resulting in a ground water flux through the alluvium of 1.64 x 10-5 cfs/sq ft
conservatively assuming a strong east/west gradient.
Total flow into the perimeter drain can then be estimated by 1.64 x 10-5 cfs/sq ft (x) 3200 ft (x) 20 ft = 1 cfs.
The carrying capacity of the perforated pipe included in the perimeter drain design was calculated using
Federal Highway Administration Drainage Design Program HY-22 to be 1.4 cfs (see attached calculation
sheet). Therefore, the perimeter drain has adequate carrying capacity with a safety factor.
In order for the proposed perimeter drain to be effective in preventing ground water mounding over the long
term, frequent inspection, regular maintenance, and occasional replacement of components, such as the
check valve at the outlet works, will be necessary. The DRMS has in other cases approved similar perimeter
drain, but these were associated with pits that were reclaimed for water storage, which is an intensively
managed post mining land use. The pending amendment to the Speer Pit permit designates general
agriculture as the post mining land use, and there is no clear pathway under that land use for assurance that
the perimeter drain will be maintained. The Applicant must address this issue through deeded covenants or
Office of Office of
Mined Land Reclamation Denver • Grand )unction • Durango Active and Inactive Mines