|
<br />VOL. 30, NO.6
<br />
<br />.\"
<br />
<br />WATER RESOURCES BULLETIN
<br />AMERICAN WATER RESOURCES ASSOCIATION
<br />
<br />DECEMBER 1994
<br />',' .
<br />
<br />
<br />SALINITY INCREASES IN THE NAVAJO AQUIFER
<br />IN SOUTHEASTERN UTAHl
<br />
<br />N
<br />......
<br />QO
<br />\Xl
<br />
<br />David L. Naftz and Lawrence E. Spangler2
<br />
<br />ABSTRACT: Salinity increases in water in some parts of the Nava-
<br />jo aquifer in southeastern t1;tah have been documented previously.
<br />The purpose of this paper i~ to use bromide, iodide, and chloride
<br />concentrations and del oxygen-IS and deuterium values in water
<br />from the study area to dete~mine if oil-field brines (OFB) could be
<br />the source of increased salinJity. Mixing-model results indicate that
<br />the bromide.to-chloride X 10,000 weight ratio characteristic of OFB
<br />in and outside the study atea could not be causing the bromide
<br />depletion with increasing salinity in the Navajo aquifer. Mixing-
<br />model results indicate that a mixture of one percent OFB with 99
<br />percent Navajo aquifer water would more than double the bromide-
<br />to-chloride weight ratio, in$tead of the observed decrease in the
<br />weight ratio with increasing chloride concentration. The trend of
<br />the mixing line representing\the isotopically enriched. samples from
<br />the Navajo aquifer does not:indicate,OFB as the sourCe of isotopi-
<br />cally enriched water; however, the simulated isotopic composition of
<br />injection water could be a saiinity source. The lighter isotopic com-
<br />position of OFB samples frain the Aneth, Ratherford, White Mesa
<br />Unit, and McElmo Creek inj~tion sites relative to the Ismay site is
<br />a result of continued recycliilg of injection water mixed with vari.
<br />ous proportions of isotopicall}' lighter make-up water from the allu-
<br />vial aquifer along the San ~uan 'River. A mixing model using the
<br />isotopic composition of the simulated injection water suggests that
<br />enriched samples from the N;avajo aquifer are composed of 36 to 75
<br />percent of the simulated injef;:tion water. However, chloride concen-
<br />trations predicted by the isot9pic mixing model are up to 13.4 times
<br />larger than the measured chloride concentrations in isotopically
<br />enriched samples from the Navajo aquifer, indicating that injection
<br />water is not the source of inq~eased salinity. Geochemical data con-
<br />sistently show that OFB anll associated injection water from the
<br />Greater Aneth Oil Field are ~not the source of salinity increases in
<br />the Navajo aquifer.
<br />(KEY TERMS: geochemistry;iground water; water quality; salinity;
<br />Greater Aneth Oil Field, Utah.)
<br />
<br />INTRODUCTION
<br />
<br />The most widesprea~ contaminant of ground water
<br />and surface water is sialinity (Richter and Kreitler,
<br />
<br />1991). On a regional level, the most significant saline
<br />sources are naturally occurring saline ground water,
<br />halite solution, sea-water intrusion, oil- and gas-field
<br />brines, agricultural by-products, salin'e s(leps, and
<br />road salt (Richter and Kreitler, 1991). The disposal of
<br />one of these saline sources, oil-field brines (OFBs),
<br />has become a major environmental concern in the oil-
<br />producing regions of the United States, as well as in
<br />other countries (U.S. Environmental Protection Agen-
<br />cy, 1977; Bair and Digel, 1990; Richter and Kreitler,
<br />1991; Shipley, 1991). Surface disposal and brine pond-
<br />ing in unlined surface pits, which have been used in
<br />the past, may have caused high potentials for fresh-
<br />water contamination, in areas where large amounts of
<br />brines were disposed of by this method (Richter and
<br />Kreitler, 1991). In addition, OFBs are typically inject-
<br />ed for secondary recovery of oil, and these brines may
<br />migrate into fresh ground water where a hydraulic
<br />connection exists between the oil reservoir and fresh
<br />water. On the basis of 1986 brine disposal data, a
<br />total of 5.8 million metric tons of salt associated with
<br />OFBs were percolated into the ground where an
<br />underground source of drinking water is not present
<br />(Richter and Kreitler,1991). Brines contain numerous
<br />trace- and major-inorganic constituents (lead, arsenic,
<br />barium, mercury, selenium, cadmium, and chloride)
<br />and trace-organic compounds (benzene, toluene,
<br />xylenes, carboxylic acids, phenols, and other volatile
<br />and semi-volatile hydrocarbons) (Thurman, 1985;
<br />Surdam and MacGowan, 1987; Bair and Dig-el, 1990;
<br />Shipley, 1991). Many of these constituents can
<br />adversely affect drinking-water supplies and biota
<br />using wetlands (Bair and Digel, 1990; ShipleY, 1991).
<br />Water-soluble polynuclear' aromatic hydrocarbons
<br />from petroleum residues found in some brines are
<br />
<br />
<br />.~
<br />:,
<br />~
<br />~
<br />:~
<br />
<br />.~
<br />~
<br />
<br />;,)j
<br />'~
<br />:k
<br />':1:
<br />i
<br />
<br />1"
<br />.k
<br />
<br />,:~
<br />
<br />;:~
<br />
<br />~~
<br />
<br />IPaper No. 94027 of the W(J.ter Resources Bulletin. Discussions are open until August 1, 1995.
<br />'Hydrologists, U.S. <kololiical Survey, 1745 West 1700 South, Salt Lake City, Utah 84104.
<br />
<br />~
<br />;-'"
<br />
<br />1119
<br />
<br />WATER RESOURCES BULLETIN
<br />
<br />:~t
<br />
<br />.,
<br />
<br />'",,-,,~ .,,:'
<br />
<br />[
<br />,. "
<br />
<br />
|