REPORT of INVESTIGATION 257 UTAH GEOLOGICAL SURVEY a Division of Utah Department of Natural Resources 2007 STATE of UTAH Jon Huntsman, Jr., Governor
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RECOMMENDED SEPTIC TANK SOIL-ABSORPTION-SYSTEM DENSITIES FOR THE SHALLOW UNCONFINED AQUIFER IN CACHE VALLEY, CACHE COUNTY, UTAH by Charles E. Bishop, Janae Wallace, and Mike Lowe Cover Photo: Large spring systems are found in the lower central area of Cache Valley, this pool is part of the Spring Creek spring system. ISBN 1-55791-771-X REPORT OF INVESTIGATION 257 UTAH GEOLOGICAL SURVEY a division of Utah Department of Natural Resources 2007 STATE OF UTAH Jon Huntsman, Jr., Governor DEPARTMENT OF NATURAL RESOURCES Michael Styler, Executive Director UTAH GEOLOGICAL SURVEY Richard G. Allis, Director PUBLICATIONS contact Natural Resources Map/Bookstore 1594 W. North Temple Salt Lake City, Utah 84116 telephone: 801-537-3320 toll-free: 1-888-UTAH MAP Web site: http://mapstore.utah.gov email: [email protected] THE UTAH GEOLOGICAL SURVEY contact 1594 W. North Temple, Suite 3110 Salt Lake City, Utah 84116 telephone: 801-537-3300 fax: 801-537-3400 Web site: http://geology.utah.gov Although this product represents the work of professional scientists, the Utah Department of Natural Resources, Utah Geological Survey, makes no warranty, expressed or implied, regarding its suitability for any particular use. The Utah Department of Natural Resources, Utah Geological Sur- vey, shall not be liable under any circumstances for any direct, indirect, special, incidental, or consequential damages with respect to claims by users of this product. CONTENTS ABSTRACT ...........................................................................................................1 INTRODUCTION . .1 PURPOSE AND SCOPE . .2 CONCEPTUAL MODEL OF THE SHALLOW UNCONFINED AQUIFER SYSTEM . .2 Introduction . .2 Surface-Water System . .2 Ground-Water System . .3 AQUIFERDATA .......................................................................................................6 Well Drilling and Slug Testing . .6 Stochastic Modeling . .7 Ground-Water Budget . .14 Ground-Water Flow Calculations . .16 Introduction . .16 Computer Modeling . .17 Calibration . .19 Results ........................................................................................................19 Modeling Limitations . .22 Septic-Tank System/Water-Quality Degradation Analyses . .22 Recommendations for Land-Use Planning . .23 SUMMARY AND CONCLUSIONS . .23 ACKNOWLEDGMENTS . .23 REFERENCES . .24 APPENDIX...........................................................................................................27 BACKGROUND INFORMATION . .27 PREVIOUS INVESTIGATIONS . .27 LOCATION AND GEOGRAPHY . .27 CLIMATE ............................................................................................................27 GEOLOGIC SETTING . .28 GROUND-WATER CONDITIONS . .28 Introduction . .28 Basin-Fill Aquifer . .28 Occurrence . .28 Depth to Ground Water . .29 Ground-Water Flow . .29 Recharge and Discharge . .29 Ground-Water Quality . .33 SEPTIC-TANK DENSITY/WATER-QUALITY DEGRADATION ANALYSIS . .33 Introduction . .33 Ground-Water Contamination from Septic-Tank Systems . .33 Pathogens......................................................................................................33 Household and Industrial Chemicals . .34 Phosphate......................................................................................................34 Nitrate ........................................................................................................34 The Mass-Balance Approach . .35 General Methods . ..