WSP01461

• File Number: 8549.800
• Description: Rio Grande Basin-Miscellaneous Small Projects and Project Studies-Rio Grande Assessment
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 2/1/1981
• Author: Brandes Kier Stecher
• Title: Water Resources Reference Base for the Assessment of the Rio Grande Region
• Water Supply Pro - Doc Type: Report/Study

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salinity levels along the River, as does evaporation from the mainstem
reservoirs.

Above Red Bluff Reservoir in the Pecos River basin in southeastern New
Mexico (WAU 130600), high saline ground water discharges enter the Pecos, and
as a result, TDS levels in the River downstream of Red Bluff Dam in Texas
(WAU 130700) exceed 7,500 mg/l about half of the time. Additional saline
aquifers, irrigation return flows and oil field runoff continue to degrade
the quality of the Pecos in Texas. In Pecos County, the annual discharge-
weighted average concentrations of TDS in the River exceed 14,000 mg/l,
however below this point, runoff and ground water from limestone aquifers
improve the water quality. The average TDS level of the Pecos River near the
Rio Grande confluence is approximately 1,600 mg/l.

Downstream of Amistad Reservoir, the salinity levels in the Rio Grande
average about 500 mg/l of TDS.

Ground Water

006S

Usable ground water supplies in the Rio Grande Region are predominantly
fresh (<1,000 mg/l TDS) and slightly saline (1,000 mg/l to 3,000 mg/l TDS).
In that irrigation is the predominant beneficial use of water in the Rio
Grande Region, total dissolved solids is a primary consideration. The pre-
sent and potential quality of ground water supplies is an impediment to
further development.

By and large, the quality of ground water in the Rio Grande Regon (in
terms of TDS) is best at the higher elevations and nearest the areas of
~echarge. In the bolsons, the principal kind of aquifer in the Rio Grande
Region, water quality is generally best near the margins of the basins and
decreases toward the center of the basins both areally and vertically.
Sodium, chloride, and sulfate ions are the main problem constituents.
Proximity to or hydraulic connection to gypsum or salt deposits in signi-
ficant portions of the Rio Grande Region adds to the problem. This is
particularly a problem in the Pecos Valley in southeastern New Mexico and
above Rio Pecos in Texas,

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