WSP07437

• File Number: 8276.851
• Description: La Verkin Springs Unit - Colorado River Salinity Control Program
• State: UT
• Basin: Colorado Mainstem
• Date: 1/1/1984
• Title: La Verkin Springs Unit Utah Preliminary Findings Report
• Water Supply Pro - Doc Type: Report/Study

The La Verkin Springs Unit was one feature of the CRWQIP that appeared to
have potential for helping reduce the salinity at Imperial Dam. Past
estimates (1981 Concluding report) attributed an annual equivalent of about
&.4 mg/L reduction at Imperial Danl to the La Verkin Springs Unit. This WdS
bdsed on a 50 year project life, 98% removd1 and aesa1ting of the springs
with approx i ma te ly 8 cfs of high qua 1 ity product wa ter retu rned to the
river.

A reand1ysis of hydrologic data during the present study has shown that the
reduction in salinity at Imperial Dam was not as great as anticipated in
the 1981 Concluding report. A more reasonable figure for salinity
reduction at Imperial ~am is 5.29 mg/L to 4.1 mg/L depending on the
alternative being consioered and the project 11fe.

The low salinity reductions attributable to the project coupled with the
relatively short project life (20 years with 98 percent spring water
removal and 50 years with 80 percent spring water removal) and the high
costs of the viable alternatives, yielded d cost effectiveness for edch
alternative in excess of 51.9 million per mg/L. (Table 1).

RESOURCES

The re1nitiat10n of the La Verk1n Springs Unit study was partially
predicated on the idea that the evaporation pond liner cost could be
substantially reduced if clay instead of plastic liners were used. A
geolog1c investigation to determine if clay in the area was suitable for
me~ting Utah state standards for pond seepage (permeab11ity coefficient of
10 cm/sec) was initiatea. It was determined that local clays, with
treatment, would be suitable for lining the ponds. However, the cost of
plastic liners has decreased to the point that they are more economical to
use thc~ clay liners, and plastic-linea panas req~ire less maintenance and
withstand weather1ng much better than clay-lined ponds.

Limited geologic investigation during 1983 ir,oicate the quantity of clay
(approximately 4,200,000 cubic yards) required for lining 1050 acres of
ponds and earthen dikes appears to be available within a 5.5 m11e radius of
the Purgatory Flats area. However, no drilling program was initiated to
firmly establish the actual quantities available. There are also a number
of mining c1ai~s throughout the area, some of which cover the pctentia1
clay borrow aredS w~ich may hirder, if not prevent, the USE of some areas.

Diversior, and evaporation of He elilire La Verkin Springs woulo result in a
d1vers1un and evaporative loss of approximately 8,500 acre-feet of water
per year to the Culoraoo River system. The Slote of Utah ~ater Resources
Department in a lett~r dated Octuber 11, 1963, stateo:

"the State Engineer feels that the most appropriate way to harld1e
the diversion of La Verkin water is with two water rights. First,
the USBR should file an app1icat1on to exchange water during the
irrigation season from the Virgin River be1uw La Verkin Springs
for water released frUIT, Quail Creek Reservoir. A contract between
0026',;2

3