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<br />. <br /> <br />N <br />t- <br />oo <br />00 <br /> <br />APPENDIX D: GROUND WATER <br /> <br />. <br /> <br />Ground water resources in the Upper Colorado River Region are <br />significant, though small, relative to such vast ground water reser- <br />voirs as the Ogallala Formation which underlies several Great Plains <br />states. Estimated total storage in the Region within the upper 100- <br />foot layer of saturated rock is in the range of SO to 115 million <br />acre-feet (maf). This is nearly four times the total active storage <br />of all the reservoirs in the Region (Price and Arnow, 1974). Yet, <br />up to the present, the utilization of this large resource has been <br />miniscule. Only 2 percent, about 122,000 acre-feet (AF), of all <br />the water withdrawn annually for use in the Region is subsurface <br />water (Price and Arnow, 1974). There are two basic reasons for <br />this lack of ground water development: (a) at past levels of econ- <br />omic development, water users (primarily irrigators) have found <br />surface supplies to be sufficiently large and more economically <br />viable than ground water, and (b) the uncertainty of finding site- <br />specific ground ~ater resour~es has discouraged its development. <br /> <br />Salinity content (total dissolved solids, or TDS) is one of the <br />largest constraints to the development of the Region's ground water <br />resources. The chemical quality of ground water is greatly influ- <br />enced by type of rock contacted. Generally, sedimentary rocks in <br />the Region such as shales, limestones, siltstones, and sandstones <br />yield TDS ranging from under 1,000 parts per ~illion (ppm) to more <br />than 35,000 ppm. Sedimentary formations are primarily found in the <br />physiographic basins such as the Green River, Great Divide, Washakie, <br />Piceance Creek, and San Juan basins (Fig. D.l). It is in these <br />regions that highly saline ground water may be found. Deeper ground <br />water generally has a higher TDS content than water in shallower <br />aquifers because it has been in contact with salins formations longer. <br />Formations such as the Paradox (found in the Paradox Valley in Colo- <br />rado and the Spanish Valley and Canyon Lands in Utah) or parts of <br />the Green River Formation (in the vicinity of Rock Springs, Wyoming) <br /> <br />aLe extensive sources of verr saline water.1 <br /> <br />1. Water salinity is classified as follows: fresh--less than 1,000 <br />mg/liter TDS; slightly saline--l,OOO to 3,000 mg/liter TOS; moderately <br />saline--3,000 to 10,000 mg/liter TDS; very saline--lO,OOO to 35,000 <br />mg/liter TDS; brine--more than 35,000 mg/liter TDS. <br /> <br />. <br /> <br />D-l <br />