WSP12002

• File Number: 8509
• Description: San Luis Valley
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 8/10/1987
• Title: San Luis Valley Confined Aquifer Study ‎(Phase I)‎ Final Report
• Water Supply Pro - Doc Type: Report/Study

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t'- 3000 feet in the central portion of the Valley, is expected to show total
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'_' di ssol ved sol ids (105) concentrations greater than 3000 . mgIJ. Above that
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approximate depth, ground water is expected to show TDS concentrations of
approximately 300 to 500 mg/l. The poor water quality in the deep confined
aquifer appears to be a result of two processes. The first is the natural
chemical evolution of ground water moving slowly toward the center of a
sedimentary basin. At the recharge areas near the basin margins, calcium-
bicarbonate (or, near the San Juans, sodium-bicarbonate) rich ground water
would ?e predominant. As the water moves slowly basinward, the water is
expected to become first rich in sulfate, and finally, near the center of the
Valley, to be strongly sodium-chloride dominant. The second process expected
to affect deep confined aquifer water chemistry occurs in and near deep-
seated, rift-related fault zones. There is evidence that these fault zones
act as conduits for upward ground water flow, so that thermal waters rich in
dissolved minerals would mix with and further degrade the pre-existing deep
confined aquifer waters. Near these rift-related fault zones, TDS
concentrations are expected to be as high as 10,000 mg/l.

c.

In the foothill s of the San Juan mountain range, the upper 2000 f~.~toJ
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the Conejos Formil.tion constitutes a thick, near-surface, and PTobilbly
r..... ~ -~..;."':-,=~--,- -'''''- "'-,>"...."'~.,~",-""""._.-""->"",,. ,-"., ", --~"
C~_,~~.~2[Ifinedaquif~It is probable that wells having acceptable water quality
(less than 1000 mg/l TDS concentration) can be constructed in this aquifer
with production rates of at least 500 gpm. In the Rio Grande fan and Saguache
Creek fan areas, it appears likely that wells could be constructed with higher
production rates (estimated at up to 2000 gpm) and acceptable water quality
(estimated at 500 mg/l TDS or less) above a depth of 1500 to 2000 feet.
Institutional aspects would be a primary concern with development of either of
these aquifer alternatives.

CONCLUSIONS
The Phase I studies, which have included analysis of Landsat Thematic
Mapper (TM) and Heat Capacity Mapping Mission (HCMM) satellite images, have
produced one of the most extensive evaluations of the geologic structure that
has been performed by any entity for the San Luis Valley aquifers. This

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