WSP00401

• File Number: 8443.400
• Description: Narrows Unit - Reports
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/1/1978
• Author: US DoI BoR
• Title: Special Report Investigation of Review Issues Narrows Unit Colorado
• Water Supply Pro - Doc Type: Report/Study

IN REPLY
llFEIl TO:
510.

232

United States Department of the lnttirior-F;'r', ,;,,-;--
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C G 9 :OFFIC~~~Et~S?tN RAEN~~~~ri~~CTl N 1.;" t,_.,O"
ENGINEERING AND RESEAROI CENTE At:G J : :~7r
.p .0. BOX 25007
BUILDING 67. DENVER FEDERAL CENT RTo -:' tJ..~ J
DENVER:. COLORADO 80225 , -ft.,.. ..ro";, " -'-
AU6 3 0 1976

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Memorandum

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To:

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Eegional Director,
Attention: 250
From!-CTINGDirector of Design

and Construction

Denver, Colorado

Subject: Detailed Stability Study - Narrows"Dam - Narrows Unit
(Memorandum from Acting Regional Director Dated
July 28, 1976)

The detailed stability study exploration program requested by
subject memorandum has been divided into two stages: (1) suc-
surface geologic investigations and (2) permeability determinations.
The exploration program, outlined below, represents the requirements
of the first stage. Upon or near completion of the first stage,
the second stage to determine permeabilities by the pumpout test
method will be formulated.

It is requested that subsurface geologic conditions be delineated
down to the Pierre Shale throughout the area bounded by lines
2,500 feet right and 2,500 feet left (along the centerline of the
dam) from the south end of the slurry trench, and 5,000 feet upstream
and 5,000 feet downstream from the centerline of the dam.

Sufficient Denison-type drilling with continuous sampling and testing
should be performed to: (1) determine the extent, thickness, config-
uration, and physical properties of the clay layer separating the
upper and lower aquifers; and (2) determine the thickness, s"rat-
ification, physical properties, and stabilized depths to the water
table in both the upper and lower aquifers.

"

The number and location of drill holes, drilling method, and inter-
pretation and correlation of data are left to the discretio~ of the
Regional Geologist, except that one hole should be drilled on the
dam centerline at the southwest end of the slurry trench. Detailed
subsurface geologic contour maps of the study area should be prepared.
The maps should show correlations of: (1) depths to and elevations
of the Pierre Shale; (2) depths to and elevations of each ground-
water table encountered; (3) depths, thicknesses, elevations, and

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