WSP05057

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1983
• Title: Colorado River Water Quality Improvement Program - Status Report
• Water Supply Pro - Doc Type: Report/Study

select areas for early study. As a result of these investigations,
Title II of Public Law 93-320 authorized the Secretary of the Interior
to construct as the initial stage of the CRWQIP: the Paradox Valley Unit
and the Grand Valley Unit, Colorado; the Crystal Geyser Unit, Utah; and
the Las Vegas Wash Unit, Nevada. This section presents a brief description
and summary of the status of investigations and construction for each of
the projects authorized for construction.

Paradox Valley Unit, Colorado

Paradox Valley, a collapsed salt anticline, is a northwest-southeast
trending valley 3 to 5 miles wide located in an arid area of southwestern
Co 1 or ado.

Geologic investigations in the Colorado Plateau have established the
existence of a series of five major northwest-southeast trending salt anti-
clines (elongated swells) about 100 miles long. The LaSal Mountains are
perched over the center of the anticline region. Paradox Valley lies along
the axis of one of these salt anticlines and was formed from erosion of
faulted and uplifted sandstone and shale formations from above a residual
gypsum cap overlying about 14,000 feet of pure salt and salt-rich shale.
The Dolores River remained in its ancient streambed as the uplift and
erosion of the valley developed. West Paradox Creek originates in the
LaSal Mountains and flows southeastward through the northwestern half of
Paradox Valley to the Dolores River. East Paradox Creek, an intermittent
stream, drains the southeastern half of Paradox Valley before flowing into
the Dolores River.

The salinity contribution from the Paradox Valley through the Dolores River
was established to be 205,000 tons of salt per year. Analysis of 5 years
of streamflow and water qual ity records modified the previous estimate.
The brine emerges in the Dolores River at a concentration of approximately
260,000 mg/L of total dissolved solids and at a rate varying from 0.2 to
2 ft3/s.

In 1978, a DPR (Definite Plant Report) and an Environmental Impact State-
ment were completed recommending a construction plan. The'documents were
officially approved in 1979. The plan involved pumping brine from wells
paralleling the Dolores River adjacent to brine inflow areas and disposing
of it in a large evaporation pond in Dry Creek Basin. With this plan,
an anticipated 180,000 tons of salt per year would be removed from the
Colorado River resulting in a decrease in salinity of 18.2 mg/L at Imperial
Dam.

Toxic and corrosive H2S (hydrogen sulfide) gas associ ated with the brine
must be removed for surface disposal. Through pilot plant studies,
Reclamation staff members tested several methods of H2S removal.

Before installing permanent facilities, a brine inflow control verification
program was initiated. A series of 18 production wells and 100 monitoring
wells were installed, along with a temporary holding pond and 3 miles of

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