WSP08953

• File Number: 8273.300
• Description: Colorado River Basin Salinity Control - Federal Agencies - USGS
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/1/1995
• Author: USGS
• Title: Using Geochemical Data to Identify Sources of Salinity to the Freshwater Navajo Aquifer in Southeastern Utah - Aneth Technical Committee Fact Sheet
• Water Supply Pro - Doc Type: Publication

. +2.5
+2.0
+1.5 Error bar
..J for upper
:E +1.0 Paleozoic !
a: aquifer
N W mean is
II. +0.5 .:tone
~. :!: standard
<Xl ..: 0 deviation
.-::n ~
-0.5
@2
-1.0 .Gl

..

Path 1

.

Path 2

.
.

-1.5
0.001 0.01 0.1 1 10
INVERSE STRONTIUM CONCENTRATION,
IN MILLIGRAMS PER LITER

EXPlANATION

. Well completed in the Noyojo aqulfer-681Sr greater than 0.75 permll

. Well completed in the Navajo aqulfer-S87Sr less than 0.75 permil
2
o Oll.field brine sample-Number refers to multiple samples

\1 Mean value of 681Sr In upper Paleozoic aquifer-four samples used to calculate mean

.37'30"

109030'

37"15'

37"00' _.__.~--

o 5 10 MILES
,
o 5 10 KilOMETERS

109"15'

109"00'

..

~
~
(j
o
Ii
&1
o~ .:>
~,,.J,r
rJ.+
S

~UTAH
--r-- --- rARiio"NA ,----

EXPlANATION

. Well with 587Sr greater
than 0.75 permll

o Well with ,s87Sr less
than 0.75 permll

----.. Ground-water flow direction

Figure 5. (A) Variation of B"Sr values and strontium concentrations In water samples from
the study area and (8) Location of wells completed in the Navajo aquifer with large (greater
than 0.75 permil) and small (less than 0.75 permil) B"Sr values.

where ("Srf'6Sr)m is the isotope ratio of the
sample; ("Sr/8OSr).. is the isotope ratio of
seawater (0.70920); and (5"Sr is the sample
deviation from seawater expressed in units
of penniL

The (5"Sr values were detennined for 56
ground-water samples from throughout the
Aneth area (fig. 5). The (5"Sr values of the
oil-field brine samples are considerably
more negative relative to values of water
samples from the Navajo aquifer (fig. 5A),
which indicates that oil-field brines are not
the source of salinity to the Navajo aquifer.

Wells in the Navajo aquifer that have
water with (5"Sr values greater than 0.75
pennil generally are located in the northern
half of the study area, and wells that have
water with (5"Sr values less than 0.75 pennil
are located in the southern half of the study
area (figs. SA, B). This geographic
segregation of the data reflects the different
hydrologic flow paths in the Navajo aquifer.
A north-to-south ground-water flow
direction (path I) is associated with the
(5"Sr values that are greater than 0.75 pennil
and east-ta-west and south-ta-north flow
directions (path 2) are associated with (5"Sr
values that are less than 0.75 permil (fig.
5A).

As the strontium concentration increases.
flow paths I and 2 appear to converge to
the mean (5"Sr value of four water samples
from the upper Paleozoic aquifer (fig. 5A).
This convergence indicates that water from
the upper Paleozoic aquifer may be a
plausible source of salinity to the Navajo
aquifer and is in agreement with the bromide
and chloride mixing modeL Additional
geochemical and hydrological data are being
collected to investigate this source of salinity
further. The study is scheduled for
conclusion during September 1995.