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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In the A1amosa area, it appears that HSU-3 is composed predominantly of
clay-rich materials, probably from the Fish Canyon and Carpenter Ridge tuffs
and the volcaniclastic facies of the Conejos Formation. In the horst/graben
fault zone near the A1amosa Geothermal Well and the Carroll and Owens Wells,
it appears likely that clay-rich materials predominate due to chemical
alteration of volcanic rocks into clays by upwelling geothermal waters.

well

Following are further conclusions regarding HSU-3 derived from the
logging and testing:
1. None of the wells
that testing would
HSU-3.

such
for

deep-

logged
yield

or tested
a value

constructed
transmissivity

were

of

2. Ground water quality in HSU-3 appears to vary in DS
concentration from a low of between 400 and 600 mg/L to a high range
possibly greater than 10,000 mg/L. In the rift-related fault zone of
the Alamosa area, it is likely that the water quality in HSU-3 is
worse than in non-rift areas due to the presence of poor-quality
thermal waters circulating upward from great depth.
3. There appear to be sand and gravel layers within HSU-3 at
depths of 4000 to 5000 feet in the A1amosa area, though
the total thickness of these permeable units likely
comprises 20 percent or less of the total thickness of
HSU-3 in that area.
4. There is evidence of active upward ground water leakage
through low-permeability (clay) units within HSU-3 in the
A1amosa area. This activity may be due to proximity to
rift-related faulting. The rates of upward leakage within HSU-3
appear to average about 0.7 feet per year.
5. There is evidence of downward vertical leakage from HSU-2 into HSU-3
in the Alamosa area. The one-dimensional view provided by the well
logs may imply that there is attendant lateral movement
of ground water through bedding planes or fault planes at the
boundary of HSU-2 and HSU-3, or that there may be ground water
movement out of the central Valley area, most likely to the south.

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