WSP00412

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1982
• Author: USDA
• Title: Colorado River Water Quality Improvement Program - Final Environmental Impact Statement for Lower Gunnison Basin Unit - Montrose and Delta Counties CO and Uintah Basin Unit
• Water Supply Pro - Doc Type: EIS

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SL'lt'lARY - LQIIER GliNNISON BASIN W;1T

This CSDA salinIty control study of the Lo~er Gunnison Basin Unil of the Colorado
River Water Quality Improvement Program ~as carried out under Public Law 93-320,
the Colorado River Basin Salinity Control Act, dated June 24, 1974, as a means
to implement the salinity control POlICY adopted for the Colorado River.
Irrigated agriculture on 171.000 acres in the Lower Gunnison River Valley
contributes about 840,000 tons of sdlt to the Colorado RIver annually. ~easures
for improved management of irrigation water Including land leveling, measuring
of water onto the fields and lining oofdrm and off-farm earthern ditches and
laterals could reduce the Colorado River's salt load by as much as 500.000
tons. reducing salinity concentrations of the Colorado River at Imperial Dam
by 52 milligrams per liter. Ho....ever. the practical limit of reduction is
about 420.000 tons. or 44 milligrams per liter. Local benefits resulting from
these improvements ~ould be reflected in reduced costs of production. improved
irrigation systems and increased crop yields. Improvements at this level
could, based on a ~orst-case analysis. adversely impact up to 13.200 acres of
the 14.800 acres of irrigation influenced wetlands that have developed as a
result of introducing irrigation into the valley about 100 years ago. There
are an additional 24.800 acres of riparian ~etlands that would not be adversely
affected.

Eight alternative plans address four levels of resource development for reducing
the river's salt load. These levels are: a continuation of ongoing USDA pro-
grams (no accelerated action), onfarm irrigation wdter management (nonstructural
alternative), onfarm ditch lining only. and combining improved onfarm irrigation
water management ~ith ditch lining at two options of onfarm improvement (manual
or automatic). Lining of off-farm laterals is displayed as a supplemental
action to six of these alternatives.

Plan 7 1S recommended for implementation and was selected ~fter reviewlng the
eight candidate plans I..ith farmers and ranchers in the valley; I.'ith officials
from local. state and federal agencies; with other interested groups; and
after considering comments on the draft report received from public review.
Major factors influencing the selection include the desires of local lando~ners
dnd operators, cost effective salinity reduction. overall implementation cost.
and program administration.

Plan 7 includes improvement of off-farm laterals in addition to those needed
for proper operation of the onfarm improvements. The implementation period
should be ten years and program effectiveness should be evaluated at three-year
intervals to determine if the program is achieving the expected degree of
salinity reduction.

The total lnstallation cost including mitigation of Plan 7 is estimated to be
$169,400,000. It is recommended that the federal government share the construc-
tion cost at a rate not greater than 75 percent. At 75 percent cost-share the
cost to the federal government is $137.B85.000 over the 10-year implementation
period. consisting of 594.545,000 for construction, 525,740,000 for administrative
and technical assistance. and $17,600,000 to mitigate the loss of habitat
values. The total cost to the local people lS estimdted to be 531,515.000 for
construction and $800,000 per year for operation, maintenance and replacement
after the program is fully implemented.

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