#ALCIUM#A -AGNESIUM-G L HLORIDE# # / 3 (YDROGEOLOGYOFTHE5NCONSOLIDATED3EDIMENTS ULFATE3 MENTS 3 G 7ATER1UALITY AND'ROUND 7ATER3URFACE 7ATER%XCHANGESE 7ATER%XCHAN M ) G E E G M ) INTHE-ETHOW2IVER"ASIN /KANOGAN#OUNTY 7ASHINGTONOUNTY 7ASHING -G- 3/ 3ODIUM.A 0OTASSIUM+ / # ( E T 7ATER 2ESOURCES)NVESTIGATIONS2EPORT A N G O B R - A 3 IC U " LF A TE 0REPAREDINCOOPERATIONWITH 3 / AGNESIUM # / - /+!./'!.#/5.49 E T A N O B R A # TRATE./ 0HOTOGRAPHOFTHE-ETHOW2IVERmOWINGTHROUGHAFORESTEDmOODPLAININ*UNENEAR&AWN#REEK -AZAMA 7ASHINGTON 0HOTOGRAPHTAKENBY#HRISTOPHER+ONRAD 53'EOLOGICAL3URVEY 53$%0!24-%.4/&4(%).4%2)/2 53'%/,/')#!,3526%9 Hydrogeology of the Unconsolidated Sediments, Water Quality, and Ground-Water/Surface-Water Exchanges in the Methow River Basin, Okanogan County, Washington By Christopher P. Konrad, Brian W. Drost, and Richard J. Wagner U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 03-4244 Prepared in cooperation with OKANOGAN COUNTY Tacoma, Washington 2003 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information write to: Copies of this report can be purchased from: Director, Washington Water Science Center U.S. Geological Survey U.S. Geological Survey Information Services 1201 Pacific Avenue – Suite 600 Building 810 Tacoma, Washington 98402 Box 25286, Federal Center http://wa.water.usgs.gov Denver, CO 80225-0286 Suggested citation: Konrad, C.P., Drost, B.W., and Wagner, R.J., 2003, Hydrogeology of the unconsolidated sediments, water quality, and ground-water/surface-water exchanges in the Methow River Basin, Okanogan County, Washington: U.S. Geological Survey Water-Resources Investigations Report 03-4244, 137 p. CONTENTS Abstract ................................................................................................................................................................ 1 Introduction .......................................................................................................................................................... 2 Purpose and Scope ...................................................................................................................................... 2 Acknowledgments....................................................................................................................................... 4 Description of Study Area........................................................................................................................... 4 Geology....................................................................................................................................................... 5 Hydrogeology of Unconsolidated Sediments....................................................................................................... 7 Methods....................................................................................................................................................... 7 Well Inventory and Water-Level Measurements............................................................................... 7 Hydrogeologic Interpretation............................................................................................................. 10 Hydraulic Conductivity...................................................................................................................... 11 Hydrogeologic Units ................................................................................................................................... 11 Water Levels in the Unconsolidated Aquifer.............................................................................................. 14 Water Quality ....................................................................................................................................................... 15 Previous Studies.......................................................................................................................................... 15 Sampling and Analytical Procedures .......................................................................................................... 17 Surface-Water Sampling.................................................................................................................... 17 Ground-Water Sampling.................................................................................................................... 20 Laboratory Methods........................................................................................................................... 20 Quality Assurance ....................................................................................................................................... 22 Results of Water-Quality Analyses............................................................................................................. 22 Nitrate and Chloride as Contaminant Indicators................................................................................ 25 Lead and Arsenic as Contaminant Indicators .................................................................................... 25 Ionic Composition of Surface and Ground Water ............................................................................. 26 Comparison of Water-Quality Results with Historical Records........................................................ 30 Exchanges Between Ground and Surface Water in the Methow River Valley and Lower Twisp River Valley .............................................................................................................................. 31 Previous Studies.......................................................................................................................................... 31 Methods for Analyzing Ground-Water and Surface-Water Exchanges...................................................... 32 Surface-Water Discharge Balance ..................................................................................................... 33 Exchanges During Low-Flow Conditions ................................................................................ 33 Daily Gains and Losses in Streamflow..................................................................................... 33 Uncertainty of Calculated Daily Gains and Losses in Streamflow........................................... 36 Continuous Ground-Water Levels in the Lower Twisp River Valley ............................................... 36 Estimates of Aquifer Recharge from Irrigation Canals Using a Surface-Water Discharge Balance................................................................................................................. 39 Methods for Developing a Water Budget ................................................................................................... 39 Gains and Losses in Streamflow Along the Methow River........................................................................ 40 Spatial Patterns During Low-Flow Conditions.................................................................................. 40 Annual and Seasonal Patterns............................................................................................................ 43 Gains and Losses in Streamflow Along the Lower Twisp River................................................................ 45 Spatial Patterns During Low-Flow Conditions.................................................................................. 46 Annual and Seasonal Patterns............................................................................................................ 47 Ground-Water Levels and Timing of Aquifer Recharge in the Lower Twisp River Valley ...................... 49 Estimates of Aquifer Recharge by Rivers and Irrigation Canals in the Methow River Basin.................... 52 Water Budget for the Methow River Basin................................................................................................. 54 Summary .............................................................................................................................................................. 55 References Cited .................................................................................................................................................. 56 Contents iii PLATE Plate 1. Maps showing thickness and extent of unconsolidated sediments and altitudes and seasonal fluctuations of the potentiometric surface, Methow River Basin, Okanogan County, Washington. FIGURES Figure 1. Map showing location of study area and streamflow-gaging stations in the Methow River Basin, Okanogan County, Washington...................................................................... 3 Figure 2. Map showing surficial geology of the Methow River Basin, Okanogan County, Washington......... 6 Figure 3. Map showing location of wells used to study the hydrogeology, quality of water, and ground-water/surface-water exchange in the Methow River Basin, Okanogan County, Washington ........................................................................................................................................ 8 Figure 4. Diagram showing well-numbering system used in Washington ....................................................... 9 Figure 5. Map showing thickness