PROJ00537

• Contract/PO #: C153766
• Contractor Name: U. S. Geological Survey
• Contract Type: Grant
• Water District: 0
• County: Boulder
• Loan Projects - Doc Type: Contract Documents

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D. OBJECTIVES: It is here proposed that an intensive mapping of shallow aquifers in the
stud y area be undertaken to provide detailed maps of the location and
thickness of th~ aquifers, the altitude of the water-table and direction of
ground-water movement, depth to the water table, saturated thickness.
altitude of the buried bedrock surface. and general water quality of the
shallow aquifers (Fig I). Bedrock aquifer mapping will include the outcrop
pattern (areas where the rocks of the bedrock aquifer are present at the
land surface) and the subcrop pattern I,areas where the bedrock aquifers ar.:
directly under an alluvial aquifer).

E. APPROACH: The approach used to map the shallow aquifers involves compiling data
from wells and test holes on the thickness of unconsolidated sediments
overlying bedrock, and on 1he depth to water in wells. These data are used
to map I) the thickness of the unconsolidated sediments (Fig. I ,'''A''), and
2) the altitude of the water table (Fig I, "E"). These two maps are
digitized and used ).Vith digital elevation models of the land surface altitude
in a geographic information system (GIS). The GIS is used to calculate
and contour maps of 3) the altitude of the buried bedrock surface (Fig I,
F=D-A), 4) the depth to the water table (Fig I, B=D-E), and 5) the
saturated thickness of the shallow aquifer (Fig I, C=E-F). Although this
conceptual approach is straight forward, compiling the data and
constructing the maps is time consuming and is a difficult undertaking in
GIS technology. Historical water-quality data for wells and test holes are
used to map the general water-quality characteristics of the shallow
aquifers.

The outcrop and subcrop patterns of the bedrock aquifers are defined by
field mapping of outcrops and bystruclUral mapping of the top and base of
the bedrock aquifer. The iotersection of the structure surfaces with the
land surface aids in defining the outcrop pattern. The intersection of the
structural surfaces with the surface of the base of the alluvium defines the
subcrop pattern.

Historically, many water wells have been constructed along the valleys of
the South Platte River and the principal tributaries. As a result.
considerable well data are held in the files of the U.S. Geological Survey
and the State Engineer's Office. These data generally will be adequate to
define the altitude of the bedrock surface and the water-table in the valleys.
However, fewer well data exist for the upland areas between stream
valleys, and additional data will be needed in these areas.

Data for test wells constructed to monitor underground storage tanks are
held by the Colorado Department of Health; data for test wells constructed

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