WSP12268

• File Number: 8509
• Description: San Luis Valley
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 6/1/1987
• Title: Interim Task 5 Report Deep Well Testing & field Investigation - San Luis Valley Confined Aquifer Study - Phase 1
• Water Supply Pro - Doc Type: Report/Study

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...-..,
,~from its surroundings. The well flows, but at a rate too small to be measured
~eaSilY; the flow is probably on the order of one gallon per day. Since the
<:...:>piezometric head is at the ground surface, and the well had remained
r"~,
-'undisturbed from June 9, 1982 (Energy Services, Inc., 1983) to August 26,
1986, (a period of 1539 days) the geothermal well constitutes an ideal
temperature-monitoring hole.

To reduce turbulence within the well
first to be run in the geothermal well.
run going down the hole, rather than up

casing, the
In addition,
the hole after

temperature log was the
the temperature log was
taggi ng bottom.

Figure 2.10 is a graph of temperature versus depth for the Alamosa
Geothermal Well, along with other measured and calculated borehole
temperatures for the San Luis Valley (8urroughs, 1981). This graph shows that
the geothermal gradient at this location is greater than has been estimated in
earlier studies. The gradient is approximately 2.9 degrees F per 100 feet of
depth. This is equivalent to about 47 degrees C per kilometer of depth.
Downward extrapolation of a linear best-fit gradient line to the temperature
data for the Alamosa Geothermal Well indicates that temperatures in the range
of 330 to 350 degrees F at a depth of 10,000 feet can be expected. This
temperature gradient falls within the range estimated for the A1amosa area of
the Rio Grande Rift by a study of shallow heat-flow test holes less than 300
feet deep (Zacharakis et a1, 1983).

Vertical leakage of ground water through confining beds from the shallow
confined aquifer to the unconfined aquifer has been recognized in the San Luis
Valley. There is also potential for a component of vertical leakage between
aquifer layers of the deep confined aquifer. The temperature log of the
Alamosa Geothermal Well has enabled the study team to identify vertical
leakage within HSU-3, between HSU-3 and HSU-2, and to estimate the rate of
the leakage. It is believed that this is the first direct evidence of the
rate of vertical leakage in the deep confined aquifer.

The method used is described in papers by Robert W. Stallman (1963), J.D.
8redehoeft and I.S. Papadopulos (1965) and Michael L. Sorey (1971). By making

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