BOARD00714

• Board Meeting Date: 7/9/1975
• Description: Agenda or Table of Contents, Minutes, Resolution
• Board Meetings - Doc Type: Meeting

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exposing a residual gypsum cap which covers about 15,000 feet of nearly
pure salt and salt-rich shale.

The geologic development of the valley is somewhat unique. Briefly
stated, the emergence of distant mountainous uplifts on each side of
the area has placed intense lateral pressures on the intervening
sedimentary formations, resulting in warping and fracturing along weak
zones. Under these pressures and the weight of the overlying formations,
a deeply buried layer of salt (Paradox Member) from an ancient inland
sea has flowed upward into the fractured area of the fold to create an
elongated swell known as an anticline. As this has taken place, the .
Dolores River has remained in its original streambed and, in conjunction
with weathering and erosion, has removed the upper materials to form
the valley. These geological processes are still active today in the
valley.

Ground water comes into contact with the top of the salt formation,
where it becomes nearly saturated, and surfaces as salt brine in the
channel of the Dolores River near the middle of. the valley. The effect
of the brine varies considerably, depending upon the amount of water
in the river. High riverflows mix with and considerably dilute the
brine; consequently, the salt content of the stream may increase from
250 milligrams per liter (mg/l) as it enters the valley to 450 mg/l as
it exits the valley. With low riverflows, however, the salinity of
the river increases from 1,000 mg/l to as high as 166,000 mg/l (approxi-
mately five times as saline as sea water) as it crosses Paradox Valley.

Possible OontrolMeasures

The Bureau of Reclamation is studying possible methods of controlling
the movement of brine ground water. Several of the alternatives involve
drilling a series of wells along the river near mid-valley. Prior
tests have indicated that pumping from the wells would reduce the water
pressure and prevent most of the brine from surfacing in the riverbed.
The brine from the wells could then be piped to one or more solar
evaporation ponds for evaporation. Another alternative would be to
inject the brine away from ground water movement into the salt dome
at mid-valley or into deep wells outside the area. Appropriate sites
for injection have not yet been identified, and this way of disposal
may only be a short term alternative to solar evaporation.

Another measure being considered involves routing the Dolores River
across the valley in a lined channel and allowing the ground water to
surface and evaporate in the natural floodplain. The required facil-
ities would be designed to accommodate the high spring floods of the
river.

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Before these and other plans can be adequately assessed, additional
research must be conducted to acquire more information about the
sources, behavior, and chemical composition of the ground water. While
investigations are being conducted, coordination .will be maintained
with appropriate state agencies and the Paradox Valley Unit Advisory
Team, a local interest group. The selection of a final plan will be

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