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

u.s. Department of the Interior
U.S. Geological Survey

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Navajo Aquifer, a Source
of Freshwater

Ground water is an important freshwater
source for domestic and livestock uses in
southeastem Utah because of the arid
climate and unavailability of surface water
from the San Juan River. The study area
includes aboul 1.200 square miles in lhe
southeastem corner of Utah (fig. I).
Precipitation on mountainous areas 1100th,
south. and east of the study area (fig. 2)
seeps into the Navajo and overlying aquifers
where the sandstones that contain the
aquifers are exposed at the surface along
mountain flanks. The ground water then
moves slowly away from the mountainous
areas toward the area of lowest elevation

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37"00'

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Using Geochemical Data to Identify
Sources of Salinity to the Freshwater
Navajo Aquifer in Southeastern Utah

in the region. the San Juan River. The
ground waler reappears at land surface
where it discharges as seepage to the San
Juan River or is consumed by vegetation
on the flood plain. Generally, wells finished
in the Navajo aquifer near the San Juan
River do not require pumping because water
flows freely from the well casing when it
is not sealed.
Salinity increases in water in some parts
of the Navajo aquifer in southeastern Utah
(fig. I) have been documented in recent
years by the U.s. Geological Survey (Avery,
1986; Kimball, 1992; Spangler, 1992). Oil
is produced in this part of Utah, and saline
ground water, which is produced with the
oil (referred to as "oil-field brine") and later
injected into the subsurface to enhance oil

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109"00'

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10 KILOMETERS

EXPlANATION

5

I~tah

Colorado
Study area

. Well penetrating
the Navajo aquifer

. Oil.field brine
sample site

. Well penetrating
the upper
Paleozoic aquifer

Figure 1. Location of selected wells where geochemical data were
collected during the study.

Aneth
Technical
Committee'
Fact Sheet

recovery, was considered to be a potential
source for the increasing salinity of water
in the Navajo aquifer (fig. 3). Additional
sources of salinity considered during the
study included water from the upper
Paleozoic aquifer and brines not associated
with oil deposits (referred to as "non-oil-
field brine") (fig. 3). Beginning in 1989,
the U.S. Geological Survey began collecting
and interpreting geochemical data from
ground-water samples in the study area to
determine the possible origines) of saline
water that could be mixing with the fresh
ground water in the Navajo aquifer.

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FIgure 2. The Abajo Mountains, a source of
recharge water to the Navajo aquifer in the
study area.

'The Aneth Technical Committee, which comprises
State, Tribal, and Federal government agencies as well
as private oil companies, is a liaison group formed to
investigate the source(s) and process(es) that cause
the obselVed salinity increases in the freshwater Navajo
aquifer in the vicinity of the Greater Aneth Oil Field.
Represented on the technical connnittee are the Bureau
of Reclamation; the Bureau of Land Management;
U.S. Environmental Protection Agency; the Bureau
of Indian Affairs; Texaco Exploration and Production.
loc.; Mobil Exploration and Producing U.S., Inc.; the
Utah Division of Oil, Gas, and Mining; the Navajo
Environmental Protection Administration; Navajo
Water Resources Management; and the U.S. Geological
Survey.