Nitrate, Arsenic and Selenium Concentrations in The Pecos Valley Aquifer, West Texas, USA Page: 229
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Int. J. Environ. Res., 4(2).229-236,Spring 2010
Nitrate, Arsenic and Selenium Concentrations in The Pecos
Valley Aquifer, West Texas,USA
Hudak, P. F.
Department of Geography and Environmental Science Program, University of North
Texas, 1155 Union Circle #305279, Denton, Texas 76203-5017, USA
Received 12 July 2009;
Revised 19 Oct. 2009;
Accepted 12 Nov. 2009
ABSTRACT: Nitrate, arsenic, and selenium concentrations in the Pecos Valley Aquifer of west
Texas were compiled, mapped, and analyzed in the context of local geology and land use. Alluvial
deposits of sand, silt, clay, and gravel compose the unconfined aquifer. Ranching and farming are
predominant land uses in the rural study area. Data were tabulated from 79 water wells with a median
depth of 75 m and mapped with a geographic information system (GIS). The wells were sampled
between the years 2003 and 2008. Total dissolved solids (TDS) concentrations in the aquifer were
very high, with a median value of2,687 mg/L. Approximately 18% of observations exceeded the 44.27
mg/L drinking water standard for nitrate, whereas 6% exceeded the 10 g/L standard for arsenic, and
only 4% surpassed the 50 tg/L standard for selenium. There was a statistically significant, direct
correlation between arsenic and selenium, as well as between nitrate and selenium concentrations.
Moreover, arsenic and selenium concentrations were significantly higher in shallower wells. Prob-
able sources of groundwater contamination in the study area include natural (geological) sources
and agricultural activity.
Key words: Nitrate, Arsenic, Selenium, Groundwater, Texas
The objective of this study was to compile, map,
and evaluate nitrate, arsenic, and selenium levels
in groundwater within the Pecos Valley Aquifer
beneath a six-county area of west Texas (Fig. 1).
Agricultural and oilfield activity, as well as natural
sources, are potential sources of groundwater pol-
lution in the study area.
Nitrate, arsenic, and selenium in drinking wa-
ter pose health risks. Worldwide, nitrate is one of
the most common contaminants in groundwater
(Strebel et al., 1989; Spalding and Exner, 1993;
Lagerstedt et al., 1994; Zhang et al., 1996;
Kacaroglu and Gunay, 1997; Nolan et al., 1997;
Pacheco and Cabrera, 1997). Nitrate can cause
methemoglobinemia and non-Hodgkin's lymphoma
(Johnson et al., 1987; Ward et al., 1994). Poten-
tial sources of nitrate in soil and groundwater in-
clude: fertilizer, animal waste, septic systems, crop
residue, soil organic nitrogen (in native plant detri-
*Corresponding author E-mail: firstname.lastname@example.org
tus, bacterial biomass, and soil constituents), and
municipal/industrial discharges. In aerated soils,
nitrogen compounds oxidize to soluble nitrate,
which may percolate to the saturated zone.Nitrate
in groundwater has a low tendency to adsorb to
aquifer solids. The U.S. maximum contaminant
level (MCL) for nitrate in drinking water is 44.27
mg/L (EPA, 2006).
The MCL for arsenic, a highly toxic sub-
stance, in drinking water is only 10 tg/L (EPA,
2006). Arsenic uptake can cause numerous dis-
eases, including cancer, nervous system disorders,
cardiovascular problems, kidney and liver disease,
diabetes, and respiratory problems (EPA, 2002).
Arsenic has been documented in drinking water
in several countries, including Argentina,
Bangladesh, China, Chile, Ghana, Hungary, In-
dia, Mexico, Thailand, and the U.S. (Nicolli et
al., 1989; Bagla and Kaiser, 1996; Williams et
al., 1996; Nickson et al., 1998; Nimick, 1998;
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Hudak, Paul F. Nitrate, Arsenic and Selenium Concentrations in The Pecos Valley Aquifer, West Texas, USA, article, 2010; [Tehran, Iran]. (digital.library.unt.edu/ark:/67531/metadc152432/m1/1/: accessed February 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Arts and Sciences.