PROJ00173

• Contract/PO #: C153369
• Contractor Name: St. Vrain and Left Hand Water Conservancy District
• Water District: 0
• County: Boulder
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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ENGINEERING GEOLOGIC FEASIBILITY STUDY
PROPOSED COFFINTOP DAM AND RESERVOIR
BOULDER COUNTY COLORADO

SECTION 1. INTRODUCTION

On November 13, 1981 agreement was reached between the St. Vrain & Left
Hand Water Conservancy District of Longmont, and Ueblacker Associates, Inc.,
Consulting Engineers and Geologists of Lakt'Wood, Colorado on the details of
the first Engineer-ing Geologic Feasibility Study of the proposed Coffintop dam
and reservoir site.

The following definitions may help to clarify the title, and meaning of
this report: "Engineering geology" means the discipl ine of applying
geological data, techniques and principles to the study of naturally-occurring
rock and soil materials or subsurface fluids. The purpose of engineering
geologic investigations is to assure that geologic factors which affect the
planning, design, construction, operation and maintenance of engineered works
are recognized, adequately interpreted and presented for use in engineering
practice. "Feasibility" refers to the extent to which it is probable that a
given project may be built and operated in a safe, sound, and economical
manner.

By the contract agreement, "the purpose of this investigation shall be to
assess the feasibility of the dam and reservoir sites in the Study Area in
relation to geological conditions as derived from a limited amount of geologic
mapping on the surface in the area of the reservoir and dam site, and
preliminary subsurface investigation by exploratory drilling at strategic
locations along the dam axis, and having positively assessed such feasibility,
to formulate a geotechnical investigative program which may include (a)
additional direct and other indirect subsurface exploration; and (2) more
detailed surficial geological analyses in identified potential problem
areas. · Th is is a prudent and order ly approach to a cr i t i ca 1 and comp 1 ex
program. The limit on the investigation requires that the most readily
available data from the surface be applied to the feasibility first, and then
to a planned system of study which eliminates the waste of random drilling and
digging. For this study the drilling consisted of just three drill holes, for
which the locations were carefully selected through examination of the
information obtained by the surface study.

UEBLACKER ASSOCIATES, INCo