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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temperature measurements in a nonflowing well which is in thermal equilibrium
with its surroundings, estimates of vertical leakage rates, and whether the
leakage is upward or downward, can be made. The A1amosa Geothermal Well
appeared ideally suited for this type of analysis. The temperature log of the
Carroll Well was unsuitable, since the well was flowing at the time of the
temperature logging.

Since piezometric head data were not available for the deep confined
aquifer, we were not able to take the analysis one desirable step further,
which would be computation of hydraulic conductivity values for the deep
confined aquifer.

Table 2.1 is a tabulation of calculated vertical leakage rates for three
depth intervals of the Alamosa Geothermal Well. These three intervals
exhibited measurable local changes in geothermal gradient, as compared with
the rest of the borehole. There were three to four different calculations of
leakage rate made for each interval, due to the difficulty in choosing the
exact depth points at which the temperature log shows a departure from the
average geothermal gradi ent. Other i nterva 1 s exhibited noti ceab 1 e local
departure from the average gradient, but were not of sufficient amplitude to
be usable in this type of analysis.

The results of the leakage-rate analysis show there is upward leakage at
depths greater than 4000 feet, at a rate probably on the order of several
tenths of a foot per year. This is a substantial fraction of the rate of
upward leakage earlier studies have shown for the upper confined aquifer into
the unconfined aquifer. Emery and others (1973) indicate an estimated upward
leakage rate from the upper confined aquifer into the unconfined aquifer of
0.6 foot per year to 0.8 foot per year. Zorich-Erker Engineering, Inc. (1980)
estimated upward leakage to be approximately 0.055 foot per year.

The analysis of depth interval A shown in Table 2.1 appears to indicate
a downward vertical component of leakage from HSU-2 into HSU-3. This may
imply that there are active zones of ground water circulation between HSU-2
and HSU-3 not only vertically, but also laterally either along near1y-

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