WSP08418

• File Number: 8220.114.I
• Description: Dolores Participating Project
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 3/24/1989
• Author: USDOI-BOR
• Title: Final Supplement to the Final Environmental Statement
• Water Supply Pro - Doc Type: EIS

SUMMARY (Continued)

Purpose and Need

The purpose of this Draft Supplement to the Final Environmental
Statement is to describe the environmental impacts that would occur from
the proposed modifications of adding salinity control as a purpose to the
Dolores Project in southwestern Colorado and of changing the alignment
of the Towaoc Canal from the west to the east of Cortez. Both of these
modifications would occur in the McElmo Creek drainage, and this supple-
ment primarily focuses on that drainage. The FES was completed in April
1977 and filed with the Council on Environmental Quality on May 9, 1977
(FES 77-12). A Finding of No Significant Impact on the addition of two
hydroelectric powerplants to the project was approved on May 11, 1981.

The salinity control modification would include lining sections of
the Lone Pine and Upper Hermana irrigation laterals in the MVIC system
to prevent seepage; abandoning the Rocky Ford Ditch', a major contributor
of salt, and incorporating its flows into the new alignment of the
Towaoc Canal east of Cortez; abandoning the MVIC's Lower Hermana Lateral
and Highline Ditch and also including their flows, along with the Ute
Mountain Ute Indian Tribe's full service irrigation project water sup-
ply, in the Towaoc Canal; and constructing eight buried pipe laterals
from the Towaoc Canal to the Rocky Ford Ditch service area.

In the Colorado River Basin, salt pickup from the McElmo Creek
drainage and other sources has resulted in a deterioration of the quality
of Colorado River water over the long term as river flows have been de-
veloped for man's beneficial use. At its headwaters in the mountains of
north-central Colorado, the Colorado River has a salinity concentration
of approximately 50 milligrams per liter (mg/L). Downstream the concen-
t rat ion progressively increases because of irrigation diversions and
salt contributions from a variety of sources; in 1985, salinity averaged
607 mg/L at Imperial Dam, the last major diversion point in the United
States. Future water development in the basin is projected to increase
salinity to an average of 963 mg/L at Imperial Dam by the year 2010.
Peak salinities are predicted to approach 1,200 mg/L in some years.

In response to the Federal Water Pollution Control Act and its
amendments (Public Law 92-500), the seven Colorado River Basin States1/
in 1972 adopted the Environmental Protection Agency approved numeric
criteria for three points on the lower Colorado River as shown in Summary
Table 1 on the following page.

1/ The waters of the Colorado River are divided by a compact agreed
to by the seven Colorado River Basin States (Arizona, California, Colo-
rado, Nevada, New Mexico, Utah, and Hymning).

s-2