WSP05903

• File Number: 8583
• Description: Rio Grande Decision Support System
• State: CO
• Basin: Rio Grande
• Water Division: 3
• Date: 2/1/1998
• Author: Dr. John W. Hernande
• Title: Evaluation Of Salvage Well Production Problems In The Closed Basin Of The San Luis Valley Colorado
• Water Supply Pro - Doc Type: Report/Study

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

00169,.

Siebenthal does not provide any extensive description of the nature of the fill in the

unconfined shallow aquifer that makes up the top 80 to 90 feet of the Closed Basin, He does

report on the Quaternary deposits as being comprised of sand dunes, alluvial fans, alluvium, and

alkali-lake deposits (USGS, 1910, page 47), One alkali-lake that he discusses is a one-acre lake

in the Bureau's Project area, just east of San Luis Lake (Section 30, T. 40 N" R. 12 E,),The lake

is described as being "practically solid crystallized sodium carbonate" from which the mineral

was harvested (USGS, 1910, page 50),

Water Quality in the Closed Basin Shallow Aquifer

The San Luis Valley probably had its origin as a depression of the earlier Santa Fe

formation and a "down warping" of its center to allow the formation of an extensive lake that

was subsequently filled by a series of depositions of clay and sand (USGS, 1910, page 52),

During dry periods this lake diminished in size and due to evaporation formed alkaline zones

where high total dissolved solids in the shallow ground-water is likely to be found today, The

lake evidently supported the growth of vegetation such as mosses and algae, resulting in the

deposition of organic matter in the valley fill,

While probably more representative of the artesian zones than the shallow aquifer,

Siebenthal reports that fresh-water shells, fish bones, bird bones, and bits of wood, roots, leaves,

seeds and peat-moss are recovered from wells all over the basin, This report of organic matter in

the artesian formations coincides with the finding of methane in the deeper wells, The contour

map in Siebenthal's report shows a closed loop that covers much of the Closed Basin as the area

where methane is found in Valley wells, The methane production area has a north-south length

of about 30 miles, and an east-west width of about 8 miles, split along the two sides of the trough

of the Valley (USGS, 1910, page 81),

10