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

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

(,J
en
CD
C'J
(:J the contact between HSU-2 and HSU-3. Fluid resistivity, downhole flowmeter,
r' .
--, and temperature logs of the Carroll Well indicate a water-quality change from
about 220-240 mg/L DS above 2080 feet, to about 400 mg/L DS below that depth,
Gamma and neutron logs of the Alamosa Geothermal Well indicate an abrupt
increase in clay content below about 2000 feet. This change is strongly
evident for the Alamosa area, but may be present only in areas in and near
rift-related faults, With the present data set on the deep confined aquifer,
we are not able to say with confidence whether this change between HSU-2 and
HSU-3 is present beneath most of the Valley, or only at specific locations,
, I I
'~' \i,' I I.
~ ,
Temperature logging in the Alamosa Geothermal Well indicates upward
leakage of ground water within HSU-3 at depths greater than 4000 feet and
downward leakage in HSU-2 at a depth of 2000 - 2500 feet. This apparent
movement into the 2500 to 4000-foot stratum may imply that there is also
attendant lateral movement at the HSU-2/HSU-3 contact. These conclusions have
been reached by analysis of local temperature variations with depth, as
measured by the temperature logging of the Alamosa Geothermal Well. The
temperature log yielded accurate data with which to perform the analysis with
adequate precision. This is the only known deep well in the Valley to which
this method can be applied, so the leakage conditions at other locations in
the Valley remain unknown.

''--I '",- ),;(..;: \,

\,c

j

\

,

Transmissivity of HSU-2 is estimated to be approximately 132,000 gpd/ft
in the Hooper area, based on testing of the Hooper Pool Well. This agrees well
with earl ier studies of the upper confined aquifer (Emery et al, 1973). In
the Alamosa area, testing of the Carroll Well yielded estimates of
transmissivity of HSU-2 ranging from 4500 to 13,900 gpd/ft, This range is
significantly lower than earlier studies have estimated (Emery et al, 1973),
and may be due to plugging of casin9 slots in the well.

Dissolved solids concentration is expected to be in the range of 400 mg/L
to greater than 10,000 mg/L in the Hooper and Alamosa areas. It is expected
that the rift-related fault zone in the Alamosa area would exhibit poorer
water quality in HSU-3 than in non-rifted areas, due to the presence of poor-
qu~lity thermal waters circulating upward from great depth. This conclusion

i i