PERMFILE115755

• Permit No: M1999120
• IBM Index Class Name: Permit File
• Doc Date: 3/22/2000
• Doc Name: SLURRY WALL AND INTERIOR DIKE L G EVERIST INC FORT LUPTON SAND AND GRAVEL MINE FN M-99-120
• From: DMG
• To: ERICA CROSBY
• Media Type: D
• Archive: No

• • III IIIIIIIIIIIII III
999
STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Departmem of Natural Resources
1313 Sherman $t., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: March 22, 2000
DIVISION OF
MINERALS
GEOLOGY
RECLAMATION
MINING•SAFETY
TO: Erica Crosby Bill Owens
Governor
FROM: Allen Sorenson
~ Greg E. Walther
/ , Executive Director
Michael B. Long
RE: Slurry Wall and Interior Dike, L.G. Everist, Inc., Division Dnector
Ft. Lupton Sand and Gravel Mine, File No. M-99-120
Introduction
The application proposes the installation of a slurry wall around the pit area prior to commencement of
mining. Design details are provided but no specifications or quality control/quality assurance plan is
included in the application. The application proposes to bond for the cost to install the slurry wall.
Such a bond could serve as a contingency if leakage were to occur in excess of criteria established by
the Office of the State Engineer or if the slurry wall were to be damaged by pit slope failure. The unit
cost in Exhibit L used to establish the amount of required bond is $3.00 per square foot of slurry wall
assuming a 36 foot depth for the wall.
Lined reservoirs that employ slurry walls to prevent hydrologic communication with ground water are a
viable water storage alternative and are adequate to meet the developed water resources post mining
land use. However, leakage of ground water through or around the slurry wall into the pit a[ a rate in
excess of 3x0.03 ft3/day/fr' would constitute a failure to achieve the designated post mining land use
under leakage criteria established by the State Engineer. If an operator were to mine out a pit within the
perimeter of a previously installed slurry wall, and it were subsequently determined that ground water
was leaking into the pit a[ a rate in excess of 3x0.03 ft3/day/ft', the operator would be faced with the
following three options:
Improve the seal in the pit to meet the Stale Engineer's leakage criteria.
Change the post mining land use and provide water to augment for ground water leaking into the pit
that is lost to evaporation.
• Backfill the pit so that water is no longer exposed to the atmosphere.
In the event the Division were to assume responsibility for reclamation of the pit through bond
forfeiture, we may be confronted with the same situation and the same three options. Of these options,
water augmentation in the South Platte River Basin and backfilling of the pit with inert fill would be the
most costly. Also, neither of these options would result in reclamation to the develo~ed water resources
use. This leaves the option of assuring that leakage into the pit is less than 3x0.03 ft /day/ft' through
reinstallation or repair of the slurry wall.