PROJ00414

• Contract/PO #: C153326
• Contractor Name: Fruitland Mesa Water Conservancy District
• Contract Type: Grant
• Water District: 0
• County: Montrose
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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The right abutment at the dam site is composed of massive sand-
stones overlying thin, interbedded sandstones and shale. The attitude
of the massive sandstone just upstream of the right abutment is N
370E, 380SE with a prominent joint at N 370E, 50"Nw. The interbedded
gray and red sandstones and sandy shales have an attitude of N 700E,
420SE and a prominent joint at N 250E, 75"Nw to vertical. The exposed
beds at the right abutment contact of the existing dam are composed of
good quality rock. The steep upstream dip of the formations are ideal
for stability and seepage control. The seepage control is assumed to
be favorable because any seepage along the bedding would have to cross
all the interbeds, and cross joints do not appear to be continuous.

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Conditions at the left abutment are less favorable than those at

the right abutment. The left abutment is composed of thin interbedded

sandstones and shales. The massive Dakota sandstone capping the right

abutment is largely absent from the left abutment as the sandstone

appears to thin out abruptly. The dip of the interbedded sandstones

and shales on the left abutment is about 40oSE, which is also favor-

able from the standpoint of stability and seepage control. The

thinness of the beds, however, results in a higher potential for

seepage through cross joints although no seepage was noted along

either abutment contact.

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Geotechnical Investigations - General

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Due to the time and budget constraints imposed on this study, a
detailed field exploration program to investigate the embankments and
their foundations was not possible. Since five borings were drilled
into the dam and foundation by the Water and Power Resources Service
(formerly U.S. Bureau of Reclamation) in 1956, it was decided that the
present efforts should be concentrated on investigating potential
borrow areas to define the quantity and quality of available construc-
tion materials while the previous borings would be evaluated to arrive
at assumptions concerning embankment materials' and foundation condi-
t ions, which were required in designing the scheme for raising the
existing embankments. Field investigations were limited, therefore,
to the following:

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