Spatial Distribution of Solutes in Aquifer Outcrop Zones along the Brazos River, East-Central Texas Page: 598
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Solutes in Aquifer Outcrop Zones
mapped for 104 wells in the outcrop zones of the six
aquifers: Carrizo-Wilcox (20 wells), Queen City (1 well),
Sparta (2 wells), Yegua-Jackson (22 wells), Gulf Coast
(49 wells), and Brazos Alluvium (10 wells). These wells
supply public (53 wells), domestic (28 wells), irrigation
(14 wells), stock (7 wells), and other uses (2 wells).
Sampled wells had a median depth of 446 ft (136 m)
(Fig. 1). Descriptive statistics were compiled for each
solute, TDS, the chloride/bromide ratio, and well depth.
ArcView (Environmental Systems Research Institute,
Redlands, CA) was used to map well locations and
solute concentration categories.
RESULTS & DISCUSSION
Each solute concentration and well-depth
distribution was positively skewed; typical of water-quality data, this pattern reflects more observations at
lower than higher concentrations (median
concentrations and well depths were closer to minimum
than maximum values) (Table 2).
Two relatively shallow wells in the Brazos
Alluvium, in the northern part of the study area,
registered nitrate levels above the drinking water
standard (Fig. 2). These observations reflect possible
nitrogen inputs from land-surface sources, such as
agriculture. Generally, nitrate concentrations were
higher in the Brazos Alluvium, which has shallower
wells than the other aquifers; this pattern is consistent
with a nitrate origin at or near the land surface (Table
3). However, the median nitrate concentration for the
entire study area was only 0.1 mg/L; that is, nitrate is
not a significant problem over the study area.Table 2. Summary of Solute Concentrations
Solute Number of Observation Minimum Maximum Median
Observations
Nitrate (mg/L) 104 0.02-0.09 85.4 0.1
Arsenic (ug/L) 104 < 1 24.6 <2.04
Sulfate (mg/L) 104 < 1 675 16.1
Boron (ug/L) 104 < 51 6900 130
TDS (mg/L) 104 163 2568 409
Chloride (mg/L) 104 8.2 741 53
Bromide (mg/L) 104 < 0.02 3.36 0.17-0.21
Chloride/Bromide 104 46-51 > 1620 273-289
Well Depth(ft) 99 35 1500 446
Notes: 1 ft = 0.305 m; ranges reflect uncertainty in values of non-detects.
Table 3. Medians in Each Aquifer
Solute Median
BA CW GC YJ
Nitrate (m g/L) 6.3 0.16 0.02 0.18
Arsenic (ug/L) 2.2 < 2 2.07 <2
Sulfate (m g/L) 43.6 14.4 13 95.8
Boron (ug/L) 178.5 146.5 67 1375
TDS (mg/L) 605 339.5 376 951
Chloride (mg/L) 80.0 34.3 48.7 127
Bromide (m g/L) 0.5 < 0.4 0.2 0.6
Chloride/Bromide 171 179-277 303 263
Well Depth (ft) 55 465 540 400
Notes: Medians computed for aquifers with at least five observations; ranges reflect uncertainty in values of
non-detects; BA- Brazos Alluvium; CW - Carrizo-Wilcox; GC - Gulf Coast; YJ- Yegua-Jackson598
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Hudak, Paul F. Spatial Distribution of Solutes in Aquifer Outcrop Zones along the Brazos River, East-Central Texas, article, January 2011; [Tehran, Iran]. (https://digital.library.unt.edu/ark:/67531/metadc152433/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.