Bedrock Aquifers in the Northern San Rafael Swell Area, Utah, with Special Emphasis on the Navajo Sandstone
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STATE OF UTAH DEPARTMENT OF NATURAL RESOURCES Technical Publication No. 78 BEDROCK AQUIFERS IN THE NORTHERN SAN RAFAEL SWELL AREA, UTAH, WITH SPECIAL EMPHASIS ON THE NAVAJO SANDSTONE by J. W. Hood and D. J. Patterson U.S. Geological Survey Prepared by the United States Geological Survey in cooperation with the Utah Department of Natural Resources and Energy Division of Water Rights 1984 CONTENTS Page Abstract 1 Introduction 2 Purpose and scope 2 General features of the area 2 Acknowledgments 5 Previous and concurrent studies 5 Terminology 6 Well-, spring-, and miscellaneous-site-nunbering system 7 Geologic setting 9 Formations and their hydrologic characteristics 9 Navajo Sandstone 10 Structure and other factors that affect hydrology................. 21 Hydrology 28 Summ ary statern en t 28 Precipitation 28 Surface water 28 Ground water 30 Recharge 30 Occurrence and movement 31 Storage 33 Discharge 34 Navajo Sandstone aquifer 34 Other consolidated aquifers 37 Evapotranspiration 37 Chemical quality of ground water 38 Effects of large-scale withdrawals of ground water 39 Well yields and drawdown 39 Effect on flow of the Colorado River 41 Further studies needed 41 Summary and conclusions 42 References cited 44 Geohydrologic data 48 Publications of the Utah Department of Natural Resources, Division of Water Rights 118 ILLUSTRATIONS [Plates are in pocket) Plate 1. Map showing hydrologic- and geologic-data sites, climatologic data, and streamflow in the northern San Rafael Swell area, Utah. 2. Geologic map of the northern San Rafael Swell area, Utah. 3. Map showing thickness of the Navajo Sandstone in the northern San Rafael Swell area, Utah. 4. Map showing structure contours on the top of the Navajo Sandstone in the Northern San Rafael Swell area, Utah. iii ILLUSTRATIONS--Continued Page Plate 5. Map showing the approximate potentiometric surface for the Navajo Sandstone aquifer in the northern San Rafael Swell area, Utah. 6. Map showing the generalized depth to the Navajo Sandstone in the northern San Rafael Swell area, Utah. Figure 1. Map showing location and extent of the northern San Rafael Swell area 3 2. Photographs showing erosional features in the San Rafael Swell 4 3. Diagram showing well- and spring-numbering system used in Utah 8 4. Histograms showing grain-size distribution in three samples of the Navajo Sandstone from test hole NSRT-2, (D-19-12)30bba-1 11 5. Photomicrographs of sandstone specimens 12 Figures 6-8. Photographs showing: 6. Fracturing at folds and near faults 15 7. Exposures of the Navajo Sandstone and other formations 16 8. Upper contact of the Navajo Sandstone 18 9. Graphs showing parts of gamma-ray and drilling-time logs and drill-cutting description for test hole NSRT-1, (D-20-10) 6bdd-1 19 10. Graphs showing percentage of soil moisture in shallow core holes in the Navajo and Coconino Sandstone in the northern San Rafael Swell area 22 11. Photographs showing dips of formations 25 12. Photographic view downward to bottom of Black Dragon Canyon 26 13. Graphs showing water levels in observation wells 35 14. Graph showing water level in shallow core hole (D-20-13)15daa-1........................................... 36 iv TABLES Page Table 1. Codes used in identifying aquifers or geologic units in tables 9, 10,11, and 14 49 2. Description of geologic units known to underlie parts of the northern San Rafael Swell area 50 3. Results of laboratory analyses of rock samples from outcrops, test-well drill cuttings, and shallow core holes 56 4. Permeability and porosity of outcrop and core samples 60 5. Sunrnary of short aquifer tests 64 6. Sunmary of hydrologic estimates 65 7. Stream gains or losses, in acre-feet, across San Rafael Swell, 1973-79 67 8. Monthly mean discharge at streamflow-gaging stations 68 9. Records of selected water wells and test holes 72 10. Records of selected springs 78 11. Records of selected petroleum-test wells and other test holes 82 12. Selected lithologic logs of wells and test holes 99 13. Descriptions of rock samples analyzed for hydrologic properties and grain-size distribution, and of sampling sites 105 14. Selected chemical analyses of water samples fran water wells, springs, petroleum-test wells, and other test holes 112 v CONVERSION FACTORS Most values in this report are given in inch-pound units followed by metric units. The conversion factors are shown to four significant figures. In the text, however, the metric equivalents are shown only to the number of significant figures consistent with the accuracy of the value in inch-pound units. Inch-pound Metric Unit Abbreviation Unit Abbreviation (Mul tiply) (by) (to obtain) Acre 0.4047 Square hectometer hm2 0.004047 Square kilometer km2 Acre-foot acre-ft 0.001233 Cubic hectometer h~3 1233 Cubic meter m Acre-foot acre-ft/yr 0.001233 Cubic hectometer hm 3/yr per year per year Cubic foot ft3 /s 0.02832 Cubic meter per m3/s per second second Foot ft 0.3048 Meter m Foot per day ftld 0.3048 Meter per day mid Foot per mile ft/mi 0.1894 Meter per kilometer m~km Foot squared per ft2 /d 0.09290 Meter squared per m Id day day Gallon per day (gal/d)/ft 12.42 Liter per day per (L/d)/m per foot meter Gallon per gal/min 0.06309 Liter per second Lis minute Inch in. 25.40 Millimeter mm 2.540 Centimeter cm Inch per hour in./hr 25.40 Millimeter per hour mm/hr Mile mi 1.609 Kilometer km 2 2 Pound per square Ib/in 0.07031 Kilogram per square k/cm inch centimeter Square mile 2.590 Square kilometer km2 Chemical concentration and water temperature are given only in metric units. Chemical concentration is given in milligrams per liter (mg/L) or mi crograms per liter (]Jg/L). Milligrams per liter is a unit expressing the concentration of chemical constituents in solution as weight (milligrams) of solute per unit volume (liter) of water. One thousand micrograms per liter is equivalent to 1 milligram per liter. For concentrations less than 7,000 milligrams per liter, the numerical value is about the same as for concentrations in the inch-pound unit, parts per million (ppm). Water temperature is given in degrees Celsius (oC), which can be con verted to degrees Fahrenheit (OF) by the following equation: °F=1.8(OC)+32. Altitudes in this report are referenced to "National Geodetic Vertical Datum of 1929 (NGVD of 1929)." The NGVD of 1929 is a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called "Mean Sea Level." vi BEDROCK AQUIFERS IN THE NORTHERN SAN RAFAEL SWELL AREA, UTAH, WITH SPECIAL EMPHASIS ON THE NAVAJO SANDSTONE By J. W. Hood and D. J. Patterson ABSTRACT The northern San Rafael Swell area in southeastern Utah includes about 2,880 square miles (7,460 square kilometers) and ranges in altitude from about 3,290 to 7,921 feet (1,195 to 2,414 meters). Precipitation, the main source of water in the area, ranges from slightly less than 6 inches (152 milli meters) to slightly more than 12 inches (305 millimeters). Rocks that underlie the area range from Precambrian to Holocene in age. The thickness of sedimentary rocks ranges from 4,083 feet (1,244 meters) to about 30,000 feet (9,140 meters). The Entrada, Navajo, Wingate, and Coconino Sandstones and rocks of Mississippian age are considered major aquifers because of their large areal extent or thickness. Their water-yielding ability is affected mainly by faulting and folding which locally enhance ground-water circulation by fracturing, or impede circulation by offsetting the more permeable beds. Water in these aquifers ranges from fresh to briny. The total hydrologic system in the northern San Rafael Swell area has an estimated average annual inflow and outflow of about 1.3 million acre-feet (1,600 cubic hectometers), of which about 1.15 million acre-feet (1,420 cubic hectometers) is derived from precipitation on the area. An estimated 99 percent of the water available to the area is consumed by evapotranspiration. The estimated gross average annual ground-water recharge is 10,000 acre feet (12 cubic hectometers) or less, of which 3,000 acre-feet (4 cubic hectometers) recharges the Navajo Sandstone. Recoverable water stored in the Navajo, Wingate, and Coconino Sandstones is estimated to be 160 million acre feet (197,300 cubic hectometers), of which 42 million acre-feet (51,800 cubic hectometers) is in the Navajo alone. Large, long-term withdrawals from the Navajo Sandstone are marginally feasible, but only west of the San Rafael Swell, and if the wells are widely spaced. Withdrawal of 20,000 acre-feet (25 cubic hectometers) per year for 30 years probably would reduce the amount of ground water in storage by about 1.4 percent. Withdrawals of this magnitude would have a negligible effect on the flow of the Colorado River. INTRODUCTION Purpose and scope This report presents the results of a study of bedrock aquifers in the northern San Rafael Swell area, Utah (fig. 1), with special emphasis on the Navajo Sandstone of Triassic(?) and Jurassic age. The study was made by the U.S. Geological Survey in cooperation with the Utah Department of Natural Resources, Division of Water Rights. Fieldwork was done mainly during March 1979-July 1980, with supplemental testing and observations during August December 1980. The principal objectives of this study were to determine: (1) Well yields of the bedrock formations, (2) the capability of formations to yield, over the long term, water chemically suitable for presently (1980) known uses, and (3) effects of withdrawals from wells on the surface-water supply in the Colorado River Basin.