WSP05262

• File Number: 8146.400
• Description: Pueblo Dam - Reports
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 5/1/1972
• Author: US DoI BoR
• Title: Final Environmental Statement
• Water Supply Pro - Doc Type: EIS

30")~

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by the Colorado State Department of Public Health. The
hardness and dissolved solids concentrations of the
water increase downstream from Pueblo to an average of
1,200 and 2,750 p.p.m. respectively at Las Animas, Colorado.
This increase is primarily due to the accumulation of salts
in return flows of irrigated lands, and from minerals picked
up from soluble rock strata along the tributary streams.

The quality of water from wells tapping the valley alluvium
depends .mainly on the depth, quality of river water and the
proximity of irrigation to the wells. In some cases, 'the
water obtained from the wells is much harder than natural
river water. The underflow of the Arkansas River and its
tributaries contribute largely to the water supply in the
valley alluvium. This underflow is much harder than the
surface flow of the river because, like the return flows
from irrigated land, it dissolves calcium and magnesium
compounds from the formation through which it passes.

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The chemical properties and constituents found in undesir-
able concentrations in wells are iron, sulfate, fluoride,
dissolved solids, nitrate and other minerals causing hard-
ness. The dissolved solids content of water in the valley
alluvium ranges from 1,660 p.p.m. to 4,130 p.p.m., and
averages 2,700 p.p.m. The total hardness of the water in
the valley alluvium ranges from 155 p.p.m. to 1,1150 p.p.m.

The Dakota sandstone and the Cheyenne sandstone members of
the Purgatoire Formation are permeable strata. The Cheyenne
sandstone is probably the equivalent of the Lytle member of
the Purgatoire in the Pueblo Dam area. When these formations
are found near the ground surface, each strata is a source
of good quality water. The water in deep aquifers is highly
mineralized in the Arkansas Valley below Pueblo. The sub-
stances present in significant quantities are calcium,
magnesium, iron, manganese, sodium, potassium and sulfates.

Not until the Arkansas River flows through Bent and Prowers
Counties on the eastern edge of the state is the Ogallala
encountered. Water supplies derived from springs of the
Ogallala formation yield small to moderate quantities of
water to domestic and stock wells. This water is generally
of poor quality. The properties and constituents found in
undesirable concentrations include nitrate, sulfate, fluoride,
selenium, total dissolved solids and hardness. The concen-
trations of these substances are above recommended limits

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