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8.0 GROUNU-WATER QUALITY
<br />8.7 Malor Ions and Dissolved Solids
<br />Ground-Water Quality Ueleriorales from West to Easl
<br />Across Area G1
<br />The water quality deteriorates as water flows from sandstone, conglomerate, and
<br />basalt in plateaus and mesas to shale in stream valleys and plains.
<br />From west to east across the area, concentrations
<br />of dissolved solids increase and the ground water
<br />changes from bicarbonate to sulfate and chloride in
<br />composition (figs. 8.1-I and 8.1-2). The regional
<br />chemical evolution of ground water is summarized in
<br />figure 8.1-3.
<br />Area 61 is higher on the western side than on the
<br />eastern side (fig. 8.1-2), and as ground water flows
<br />down this topographic gradient, it gains dissolved
<br />solids by reaction with bedrock. Geologic forma-
<br />tions on the western side of the area are predomi-
<br />nantly sandstone and conglomerate, which consist of
<br />minerals, such as quartz, that resist reaction with
<br />ground water. Precipitation and surface water that
<br />infiltrate these rocks and become ground water arc
<br />calcium bicarbonate solutions containing I'csv dis-
<br />solved solids. Because sandstone and conglomerate
<br />minerals do not react readily with ground water, tltc
<br />ground water is little changed as it (lows through the
<br />rock. Geologic formations on the eastern side of the
<br />area are predominantly shale, which is composed of
<br />clay minerals and salts that react readily with ground
<br />water. Ground water (lowing through .shale thus
<br />becomes very mineralized. In the central part of the
<br />area, geologic formations consist of nearly equal
<br />quantities of sandstone and shale, and ground water
<br />there is intermediate irr composition and yuality
<br />between ground waters on the western and eastern
<br />sides of the area.
<br />streams, We strearnflow may be sufficient to flush
<br />out dissolved minerals and cause water in alluvium
<br />and shallow bedrock to be less mineralized than in
<br />adjacent bedrock. Ground water in volcanic-capped
<br />mesas contains few dissolved solids because the vol-
<br />canic rocks ace very permeable and rapidly transmit
<br />water. The origin of highly mineralized sodium
<br />chloride ground water near the Spanish Peaks, an
<br />intrusive stock, and related dikes is obscure, but the
<br />composition of the ground water may result from
<br />reactions with gases emanating from the igneous
<br />rocks.
<br />Geologic formations are distinguishable by their
<br />ground-water quality. The Devils Hole-Farasita, Cu-
<br />cltara Poison Canyon, and volcanic rock aquifers
<br />contain mostly calcium bicarbonate water with less
<br />than 500 milligrams per liter of dissolved solids. The
<br />Htrcrfaito Formation contains mostly calcium sulfate
<br />water with 500 to 1,500 milligrams per liter of dis-
<br />solved solids. The Raton-Vermejo-Trinidad aquifer
<br />contains mostly sodium bicarbonate water with 500
<br />to 1,5011 milligrams per liter of dissolved solids.
<br />Cretaceous shale, limestone, and sandstone contain
<br />mostly sodium sulfate, calcium sulfate, and sodium
<br />chloride water with 1,000 to more than 5,000 milli-
<br />grams per liter of dissolved solids. Within each
<br />formation, water generally is Icasl mineralized in
<br />topographically high areas and more mineralized in
<br />lopographicallyIow areas.
<br />Regional trends in ground-water quality are dis-
<br />rupted by topographic and geologic features. As
<br />ground water (lows from stream divides to stream
<br />valleys, it gains dissolved solids (fig. 8.1-2). Human
<br />activities, such as mining or irrigated agriculture,
<br />also add dissolved solids to ground water in valleys.
<br />Ground water in valleys with intermittent or ephe-
<br />meral streams is thus more mineralized than in
<br />stream-divide areas. In valleys with perennial
<br />Sources of ground-water yuality data include
<br />Griggs (1948, p. 159-176), Powell (1952, p. 30),
<br />McLaughlin and others (19(1, p. 17-18), Dinwiddie
<br />(1964, p. 15), Hart and Smith (1979, p. 50-51),
<br />Water, Waste, and Land, Ltd. (1980, appendix E),
<br />Rcpplier and others (1981, pl. 5), Howard (1982,
<br />appendix K), Kaiser Steel Corp. (written commun.,
<br />1981), and unpublished U.S. Geological Survey data.
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