Prepared in cooperation with the Skagit County Public Works Department, Washington State Department of Ecology, and Skagit County Public Utility District No. 1

Hydrogeologic Framework, Groundwater Movement, and Water Budget in Tributary Subbasins and Vicinity, Lower Skagit River Basin, Skagit and Snohomish Counties, Washington

Scientific Investigations Report 2009–5270

U.S. Department of the Interior U.S. Geological Survey Cover: Lake Creek which connects Lake McMurray to Big Lake, lower Skagit River basin, Washington. Photograph taken May 9, 2006, courtesy of Skagit County Public Works. Hydrogeologic Framework, Groundwater Movement, and Water Budget in Tributary Subbasins and Vicinity, Lower Skagit River Basin, Skagit and Snohomish Counties, Washington

By Mark E. Savoca, Kenneth H. Johnson, Steven S. Sumioka, Theresa D. Olsen, Elisabeth T. Fasser, and Raegan L. Huffman

Prepared in cooperation with the Skagit County Public Works Department, Washington State Department of Ecology, and Skagit County Public Utility District No. 1

Scientific Investigations Report 2009–5270

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2009

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Suggested citation: Savoca, M.E., Johnson, K.H., Sumioka, S.S., Olsen, T.D., Fasser, E.T., and Huffman, R.L., 2009, Hydrogeologic framework, groundwater movement, and water budget in tributary subbasins and vicinity, lower Skagit River basin, Skagit and Snohomish Counties, Washington: U.S. Geological Survey Scientific Investigations Report 2009–5270, 46 p. iii

Contents

Abstract...... 1 Introduction...... 1 Purpose and Scope...... 2 Description of Study Area...... 2 Methods of Investigation...... 4 Well Inventory and Water-Level Measurements...... 4 Hydrogeology...... 4 Streamflow...... 5 Hydrogeologic Framework...... 5 Geologic Setting...... 5 Geologic Units...... 6 Hydrogeologic Units...... 8 Hydraulic Conductivity...... 18 Groundwater Movement ...... 20 Recharge ...... 20 Groundwater-Flow Directions...... 26 Discharge...... 32 Groundwater/Surface-Water Interactions...... 34 Groundwater-Level Fluctuations...... 34 Water Budget...... 40 Summary and Conclusions...... 42 Acknowledgments...... 43 Selected References ...... 43

Plates

Plate 1. Map showing locations of selected wells, streamflow-gaging stations, and streamflow-measurement sites, and map showing generalized surficial geology in tributary subbasins and vicinity, lower Skagit River basin, Washington. Plate 2. Map and hydrogeologic sections showing surficial hydrogeology, hydrogeologic units, and locations of selected wells in tributary subbasins and vicinity, lower Skagit River basin, Washington. iv

Figures

Figure 1. Map showing location of tributary subbasins and vicinity, lower Skagit River basin, Washington…………………………………………………………………… 3 Figure 2. Map showing extent and thickness of alluvial and recessional outwash aquifer (Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington… 11 Figure 3. Map showing extent and thickness of till confining unit (Qgt) in tributary subbasins and vicinity, lower Skagit River basin, Washington……………………… 12 Figure 4. Map showing extent and thickness of advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower Skagit River basin, Washington…………… 13 Figure 5. Map showing extent and thickness of glaciolacustrine and distal outwash confining unit (Qgl) in tributary subbasins and vicinity, lower Skagit River basin, Washington…………………………………………………………………… 14 Figure 6. Map showing extent and thickness of inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower Skagit River basin, Washington…………… 15 Figure 7. Map showing extent and thickness of older till confining unit (Qot) in tributary subbasins and vicinity, lower Skagit River basin, Washington……………………… 16 Figure 8. Map showing extent and thickness of older outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, lower Skagit River basin, Washington… 17 Figure 9. Map showing extent of sedimentary aquifer (OEc) and igneous and metamorphic bedrock unit (EJTP) in tributary subbasins and vicinity, lower Skagit River basin, Washington……………………………………………………… 19 Figure 10. Map showing average annual precipitation, canopy cover, and impervious surface across the tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008………………………………………… 22 Figure 11. Graph showing precipitation-recharge relations used in this study, lower Skagit River basin, Washington……………………………………………………… 23 Figure 12. Map showing detail of distribution of impervious surfaces in tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008…………………………………………………………………… 24 Figure 13. Map showing distribution of average annual groundwater recharge from precipitation in tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008………………………………………… 25 Figure 14. Map showing water-level altitudes and direction of groundwater flow in alluvial and recessional outwash aquifer (Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008……… 27 Figure 15. Map showing water-level altitudes and direction of groundwater flow in advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008…………………… 28 Figure 16. Map showing water-level altitudes and direction of groundwater flow in inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008…………………… 29 Figure 17. Map showing water-level altitudes and direction of groundwater flow in older outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008…………………… 30 Figure 18. Map showing water-level altitudes and direction of groundwater flow in the sedimentary aquifer (OEc) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008…………………………… 31 v

Figures–Continued

Figure 19. Graph showing mean monthly streamflow (2001–08) for East Fork Nookachamps Creek at Washington State Department of Ecology streamflow-gaging station 03G100, lower Skagit River basin, Washington………… 36 Figure 20. Graph showing daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps (12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, August 1–15, 2007……… 37 Figure 21. Graph showing daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps (12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, June 10–25, 2008……………………………………………………… 37 Figure 22. Map showing locations of stream sites where streamflow was measured to determine groundwater discharge and delineate gaining and losing stream reaches in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2007 and June 2008…………………………………………… 38 Figure 23. Hydrographs of water levels in well 34N/05E-32P01, stream stage at U.S. Geological Survey steamflow-gaging station on Nookachamps Creek (12199600), and precipitation at Sedro-Woolley, lower Skagit River basin, Washington, April 2007–August 2008………………………………………………… 39 Figure 24. Hydrographs of water levels in well 33N/04E-28M01, stream stage at U.S. Geological Survey streamflow-gaging station on Fisher Creek (12200701), and precipitation at Sedro-Woolley, lower Skagit River basin, Washington, April 2007–August 2008…………………………………………………………………… 39

Tables

Table 1. Simplified geologic units defined in this study and correlation with previous investigations……………………………………………………………………… 7 Table 2. Hydrogeologic units defined in this study and correlation with geologic units defined in this study and previous investigations…………………………………… 9 Table 3. Statistical summary of hydraulic conductivity values by hydrogeologic unit in tributary subbasins and vicinity, lower Skagit River basin, Washington…………… 20 Table 4. Synoptic streamflow measurements used to determine groundwater discharge and estimates of evaporative loss from lakes in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2007 and June 2008………………………………………………………………………………… 33 Table 5. Synoptic streamflow measurements and estimates of gains and losses in tributary subbasins, lower Skagit River basin, Washington, August 2007 and June 2008…………………………………………………………………………… 35 Table 6. Statistical summary of groundwater-level fluctuations and well depth by hydrogeologic unit in tributary subbasins and vicinity, lower Skagit River basin, Washington, October 2006 through September 2008………………………………… 40 Table 7. Estimated average annual water budget for tributary subbasins, lower Skagit River basin, Washington, September 1, 2006, to August 31, 2008…………………… 41 vi

Conversion Factors, Datums, and Acronyms

Conversion Factors

Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area acre 0.4047 hectare (ha) acre 0.004047 square kilometer (km2) section (640 acres or 1 square mile) 259.0 square hectometer (hm2) square mile (mi2) 259.0 hectare (ha) square mile (mi2) 2.590 square kilometer (km2) Volume acre-foot (acre-ft) 1,233 cubic meter (m3) Flow rate acre-foot per year (acre-ft/yr) 1,233 cubic meter per year (m3/yr) foot per day (ft/d) 0.3048 meter per day (m/d) cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) gallon per day (gal/d) 0.003785 cubic meter per day (m3/d) inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32. Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C=(°F-32)/1.8. Datums Vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD88), referred to in this report as “sea level.” Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD83). Altitude, as used in this report, refers to distance above or below sea level. Acronyms ANUDEM Australian National University Digital Elevation Model DDMFZ Darington-Devils Mountain Fault Zone DEM digital elevation model DNR Washington Department of Natural Resources Ecology Washington State Department of Ecology GIS Geographic Information System GPS Global Positioning System LiDAR Light Detection and Ranging NWS National Weather Service NED National Elevation Dataset NLVD National Land Cover Database NWIS USGS National Water Information System PRISM Parameter-elevation Regressions on Independent Slopes Model PVC polyvinyl chloride USGS U.S. Geological Survey vii

Well-Numbering System

Wells in Washington State are assigned a local well number that identifies each well based on its location within a township, range, section, and 40-acre tract. For example, local well number 33N/04E-02E01 indicates that the well is in township 33 north of the Willamette Base Line, and range 4 east of the Willamette Meridian. The numbers immediately following the hyphen indicate the section (02) within the township, and the letter following the section (E) gives the 40-acre tract of the section. The two-digit sequence number (01) following the letter is used to distinguish individual wells in the same 40-acre tract. A “D” following the sequence number indicates a well that has been deepened. In the plates of this report, wells are identified using only the section and 40-acre tract, such as 02E01; the township and range are shown on the map borders.

Study area

W A S H I N G T O N

WillametteMeridian Willamette Base Line TOWNSHIP 13456

T. 7 12 18 13 33N/04E-02E01 ABCD 33 19 24 EFGH N. 30 25 JKLM 31 32 343335 36 NPQR R. 4 E. SECTION 02

Diagram showing well numbering system used in Washington. viii

This page intentionally left blank. Hydrogeologic Framework, Groundwater Movement, and Water Budget in Tributary Subbasins and Vicinity, Lower Skagit River Basin, Skagit and Snohomish Counties, Washington

By Mark E. Savoca, Kenneth H. Johnson, Steven S. Sumioka, Theresa D. Olsen, Elisabeth T. Fasser, and Raegan L. Huffman

Abstract local topographic relief (radial flow from bedrock highs) and more regional westward flow from the mountains to A study to characterize the groundwater-flow system the Puget Sound. The largest groundwater-level fluctuations in four tributary subbasins and vicinity of the lower Skagit observed during the monitoring period (October 2006 River basin was conducted by the U.S. Geological Survey to through September 2008) occurred in wells completed in the assist Skagit County and the Washington State Department sedimentary aquifer, and ranged from about 3 to 27 feet. Water of Ecology in evaluating the effects of potential groundwater levels in wells completed in unconsolidated hydrogeologic withdrawals and consumptive use on tributary streamflows. units exhibited seasonal variations ranging from less than 1 to This report presents information used to characterize the about 10 feet. groundwater and surface-water flow system in the subbasins, Synoptic streamflow measurements made in August and includes descriptions of the geology and hydrogeologic 2007 and June 2008 indicate a total groundwater discharge framework of the subbasins; groundwater recharge and to creeks in the tributary subbasin area of about 13.15 and discharge; groundwater levels and flow directions; seasonal 129.6 cubic feet per second (9,520 and 93,830 acre-feet per groundwater-level fluctuations; interactions between aquifers year), respectively. Streamflow measurements illustrate a and the surface-water system; and a water budget for the general pattern in which the upper reaches of creeks in the subbasins. study area tended to gain flow from the groundwater system, The study area covers about 247 mi2 along the Skagit and lower creek reaches tended to lose water. Large inflows River and its tributary subbasins (East Fork Nookachamps from tributaries to major creeks in the study area suggest Creek, Nookachamps Creek, Carpenter Creek, and Fisher the presence of groundwater discharge from upland areas Creek) in southwestern Skagit County and northwestern underlain by bedrock. Snohomish County, Washington. The geology of the area The groundwater system within the subbasins received records a complex history of accretion along the continental an average (September 1, 2006 to August 31, 2008) of margin, mountain building, deposition of terrestrial and about 92,400 acre-feet or about 18 inches of recharge from marine sediments, igneous intrusion, and the repeated advance precipitation a year. Most of this recharge (65 percent) and retreat of continental glaciers. A simplified surficial discharges to creeks, and only about 3 percent is withdrawn geologic map was developed from previous mapping in the from wells. The remaining groundwater recharge (32 percent) area, and geologic units were grouped into nine hydrogeologic leaves the subbasin groundwater system as discharge to the units consisting of aquifers and confining units. A surficial Skagit River and Puget Sound. hydrogeologic unit map was constructed and, with lithologic information from 296 drillers’ logs, was used to produce unit extent and thickness maps and four hydrogeologic sections. Introduction Groundwater in unconsolidated aquifers generally flows towards the northwest and west in the direction of the Skagit In Washington State, the availability of water for out- River and Puget Sound. This generalized flow pattern is likely of-stream uses must be determined before water can be complicated by the presence of low-permeability confining appropriated. This determination is most often made as part units that separate discontinuous bodies of aquifer material of an application for a water right; however, certain uses and act as local groundwater-flow barriers. Groundwater- are exempted from the water rights permitting system. To flow directions in the sedimentary aquifer likely reflect prevent water withdrawals from impacting other out-of-stream 2 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington and instream uses, Washington State may reserve a specific east by upland and mountainous terrain. The alluvial valley quantity of water in a stream basin for out-of-stream uses primarily is underlain by fluvial sand and gravel deposits as part of the regulation establishing minimum instream associated with the present and ancient Skagit River, and flows (the Instream-Flow Rule). The reservation allows new locally preserved lahar runout deposits originating from groundwater withdrawals in basins where all available water Glacier Peak, located about 55 mi east-southeast of the study is appropriated. Once the total of new withdrawals equals the area. Upland areas contain laterally discontinuous bodies of quantity specified in the reservation, subsequent new uses glacial and interglacial deposits that reflect both terrestrial and would have to find an alternative source of water, obtain an shallow marine depositional environments. Bedrock consisting existing water right, or provide compensating mitigation for of a complex assemblage of metamorphic rocks, sedimentary streamflow impacts. units, and igneous rocks underlies the alluvial valley and Recent population growth along the Interstate 5 corridor upland areas, and crops out throughout the mountainous near Mount Vernon, Washington, has led to increased water terrain. use with many new domestic wells serving residents in the The southwest flowing Skagit River receives lower Skagit River basin in areas not served by a regional streamflow from four tributary subbasins that originate public water system. Planning for future development within the mountainous interior of the study area: East Fork in the lower basin, including the reservation of water for Nookachamps Creek, Nookachamps Creek, Carpenter Creek, new domestic wells, requires identification of areas where and Fisher Creek. These creeks drain areas of about 37, 28, withdrawals from existing and new wells could adversely 19, and 10 mi2, respectively. The lower reaches of most impact streamflow in the Skagit River or its tributaries. Skagit creeks flow year-round, however, intermittent-flow conditions County, as the land-use authority for unincorporated areas are common in middle and upper creek reaches during the requires a scientifically credible basis for implementing land- summer months. Backwater conditions periodically occur use restrictions to protect instream resources. near the confluence of creeks with the Skagit River. Springs In June 2006, the USGS, in cooperation with Skagit are present throughout the study area, and contribute to late- County Public Works Department, the Washington State summer baseflow to creeks. Major lakes in the study area Department of Ecology (Ecology), and Skagit County Public include Big Lake, Clear Lake, Lake McMurray, Beaver Lake, Utility District No. 1, began a project to characterize the Barney Lake, and Sixteen Lake (fig. 1). groundwater-flow system in the tributary subbasins and The study area has a temperate marine climate with vicinity of the lower Skagit River basin. A second phase of warm, dry summers, and cool, wet winters with snow and this project will integrate this and other information into a freezing temperatures common at high altitudes. Temperatures numerical flow model to evaluate the effects of potential are moderated by the Pacific Ocean and Puget Sound, and groundwater withdrawals and consumptive use on tributary these bodies of water provide an abundant supply of moisture streamflows. for storms that typically approach the area from the west. Mean annual precipitation (average annual precipitation for the study period September 1, 2006, to August 31, 2008) Purpose and Scope varies across the study area according to distance from the Puget Sound and altitude, and ranges from about 30 in. near This report presents information used to characterize Puget Sound to greater than 120 in. in the mountains to the the groundwater-flow system in and around four subbasins east. Land-surface altitude in the study area ranges from tributary to the lower Skagit River: East Fork Nookachamps about 10 ft in the Skagit River valley to near 4,000 ft in the Creek, Nookachamps Creek, Carpenter Creek, and Fisher mountainous areas. Normal annual precipitation (average Creek. The report describes the hydrogeologic framework annual precipitation for 1971-2000) at Sedro-Woolley is of the subbasins and vicinity; groundwater recharge and 46.6 in., and at Mount Vernon is 32.7 in. (National Oceanic discharge; groundwater levels and flow directions; seasonal and Atmospheric Administration, 2007). The distribution groundwater-level fluctuations; interactions between of precipitation varies throughout the year. Summers (June- groundwater and the surface-water system; and a water budget August) typically are dry with a normal summer precipitation for the subbasins. (average “summer” precipitation for 1971–2000) of 6.4 in. at Sedro-Woolley and 4.5 in. at Mount Vernon. Winters Description of Study Area (December–February) are wetter than summers with a normal winter precipitation (average “winter” precipitation The study area covers about 247 mi2 along the Skagit for 1971–2000) of 16.4 in. at Sedro-Woolley and 11.0 in. at River and its tributary subbasins in southwestern Skagit Mount Vernon. The normal monthly temperature (average County and northwestern Snohomish County, Washington temperature for selected months for 1971–2000) at these (fig. 1). The Skagit River occupies a large, relatively flat locations ranges from about 39 oF in January to about 63 oF in alluvial valley that extends across the northern and western August (National Oceanic and Atmospheric Administration, margins of the study area, and is bounded to the south and 2007). Introduction 3

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R. 3 E. R. 4 E. R. 5 E. R. 6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 43210 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS

Figure 1. Location of tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 01 4 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Methods of Investigation bearing sediments were encountered at four locations; cores were collected, however, wells at these locations were not Methods used to compile and analyze information for the constructed (pl. 1). characterization of the groundwater and surface-water flow The spatial distribution of hydrogeologic data from system in the study area are described in this section. Methods inventoried and newly constructed wells was insufficient used to describe groundwater movement and water budget of to fully evaluate the high degree of spatial variability of the study area, are included with the respective sections later hydrogeologic units in the study area. Therefore, an additional in this report. 168 wells with available drillers’ logs were selected from USGS, Ecology, and DNR databases to help refine the hydrogeologic framework in areas where data from the Well Inventory and Water-Level Measurements original set of wells were limited (pl. 1). The approximate location of most of the additional wells had been previously Characterization of the groundwater-flow system relied established by DNR; these and the remaining well locations on the analysis of spatially distributed information about were established using the well address listed on the drillers’ groundwater levels, and the physical and hydraulic properties log and the Skagit County Assessors tax parcel database. Well of the geologic units encountered during well construction. information collected during the field inventory, monthly This information was obtained through the measurement of monitoring network, and construction of the hydrogeologic water levels in wells, and the evaluation of hydrogeologic framework were entered into the USGS National Water descriptions and well tests from well drillers’ logs. Well Information System (NWIS) database and published in Fasser records were compiled from USGS, Ecology, and Washington and Julich (2009). Department of Natural Resources (DNR) databases to identify potential wells to be used in this study. Candidate wells were selected for field inventory based on the location and depth Hydrogeology of the well, and the availability of a driller’s log. The goal of the inventory was to obtain an even distribution of wells The surficial geology for the tributary subbasins throughout the study area. However, this was not possible was compiled from previous mapping by Schuster (2000; for the entire study area because of a lack of wells in less 1:100,000), Dragovich and others (2002; 1:24,000), and populated areas. During the field inventory (August through Dragovich and DeOme (2006; 1:24,000). No attempt was October 2006), permission for access was obtained, and made to reconcile matching of surficial geologic units across synoptic water levels were measured in 128 wells (pl. 1). map boundaries; however, in some areas, modifications Water levels were measured on a monthly basis from October were made to unit designations from previous maps based 2006 through September 2008 in 62 of the inventoried wells on stratigraphic evidence obtained during this investigation, and 9 new wells constructed for this study (pl. 1). Continuous primarily drillers’ logs for field located wells. Differences in water-level recorders were installed in four of the monthly geologic unit nomenclature and map scales were addressed monitoring wells (pl. 1). through the use of simplified stratigraphy and consistent Latitude and longitude locations were determined for nomenclature that is based on the work of Dragovich and each well using a Global Positioning System (GPS) receiver others (2002). When possible, geologic units were grouped with a horizontal accuracy of one-tenth of a second (about under a single new unit designation based on similarities in 10 ft). Light Detection and Ranging (LiDAR) data were lithology and stratigraphic position to allow for a simplified used to determine the altitude of land surface at each well, and consistent representation of geology across the study area. and for the computation of water-level altitudes. LiDAR This process resulted in the grouping of 62 geologic units from data were collected and processed by a private vendor previous mapping into 18 geologic units, and the production under contract with the USGS. Vertical accuracy (typically of a simplified surficial geologic map for this study (pl. 1). ±1 ft) was evaluated for internal consistency (repeatability), These geologic units were grouped into nine hydrogeologic and conformance with independent ground-control points. units, consisting of aquifers and confining units, on the basis Water level, reported as depth to water below land surface, of lithologic (depositional facies, grain size, and sorting) was measured using a calibrated electric tape or graduated and hydrologic (hydraulic conductivity and unit geometry) steel tape, both with accuracy to 0.01 ft. All water-level characteristics. A map of the surficial distribution of these measurements were made by USGS personnel according hydrogeologic units was constructed for this study (pl. 2). The to standardized techniques of the USGS (Drost, 2005). hydrogeologic units identified in this report do not in all cases New wells were installed using direct-push technology and correspond to geologic time-stratigraphic deposits. were constructed of 1.5 in. polyvinyl chloride (PVC) pipe, Hydrogeologic sections and unit extent and thickness and 5 or 10 ft of 0.01- to 0.02-in. slotted PVC screen with maps of the tributary subbasin groundwater system were integrated sand-filter pack. Sediment cores were continuously constructed based on: (1) the simplified surficial geology, collected as the drive casing was advanced. Non-water (2) geologic and hydrogeologic interpretations, maps, and sections from previous investigations, and (3) geologic unit Hydrogeologic Framework 5 delineations made by this and previous investigations using character of the measurement section, number of observations, information collected from 296 wells. Hydrogeologic unit top stability of stage, wind, and the accuracy of depth and velocity and extent information was used to create digital elevation measurements (Rantz, 1982, p. 179). Accuracy ratings of model (DEM) surfaces in a Geographic Information System “good” indicate that the measurements are within 5 percent (GIS) database at a 30 ft cell size. The interpolation method of actual values, ratings of “fair” indicate the measurements for creating each hydrogeologic unit surface in GIS was based are within 8 percent of actual values, and ratings of “poor” on the Australian National University Digital Elevation Model indicate the measurements are not within 8 percent of actual (ANUDEM) procedure developed by Hutchinson (1989), values (assumed to be within 11 percent of actual values for using well unit picks and extent maps. Each hydrogeologic this study). unit surface was constrained to the National Elevation Dataset (NED) 30 ft DEM for land surface where the unit cropped out. Thickness maps were constructed for each hydrogeologic unit using GIS to calculate the difference between the Hydrogeologic Framework altitude of the interpolated top of the unit and the altitude This section describes the geology and hydrogeologic of the interpolated top of units underlying it. If part of a framework, which define the physical, lithologic, and hydrogeologic unit was interpolated to extend above the top hydrologic characteristics of the hydrogeologic units that of an overlying hydrogeologic unit, then minimum thickness compose the groundwater system in the tributary subbasins. values for the overlying unit were used in the calculations An understanding of these characteristics is important in to adjust the altitude of the top of the underlying unit where determining the occurrence, movement, and availability of needed. Unconsolidated hydrogeologic unit thicknesses were groundwater within the aquifer system, and the exchange of constrained by bedrock-surface data in areas with limited water between the aquifer system and surface-water features. subsurface information. Average minimum thicknesses were used to represent occurrences of unconsolidated hydrogeologic units overlying bedrock in areas of limited subsurface data. Geologic Setting In developing the hydrogeologic framework, the original data interpretations were honored as much as possible. A brief summary of major geologic events in the study The resulting interpolated hydrogeologic unit surfaces, and area is given below, and is based on the work of Hansen and calculated unit thickness, were compared to the original Mackin (1949), Easterbrook (1969), Marcus (1981), Johnson map, section, and well interpretations, and adjusted to more (1982), Booth (1994), Tabor (1994), Dragovich, and Grisamer accurately reflect the original interpretations when necessary. (1998), Dragovich and others (2002), and Dragovich and The areas where the calculated units are less accurate are in DeOme (2006). The geology of the study area records a areas of (1) data gaps, (2) where the surficial geology changes complex history of accretion along the continental margin, abruptly, and (3) where the well locations are less accurate. mountain building, deposition of terrestrial and marine sediments, igneous intrusion, and the repeated advance and retreat of continental glaciers. Bedrock in the study area Streamflow consists of: (1) complex assemblages of faulted and folded Characterization of the surface-water flow system in the low-grade metamorphic rocks formed during Late Jurassic tributary subbasins was facilitated by the installation of three or Early Cretaceous continental margin subduction; (2) USGS streamflow-gaging stations to measure streamflow on sedimentary units deposited in alluvial fan, braided stream, Nookachamps, Carpenter, and Fisher Creeks; streamflow on and near shore shallow marine settings; and (3) igneous East Fork Nookachamps Creek was already being measured intrusive and extrusive rocks that occur as dikes, sills, at an Ecology streamflow-gaging station (pl. 1). Two sets of domes, and flows (pyroclastic and lava). Metamorphic rocks synoptic streamflow measurements were made in August 2007 were likely brought to the surface by Mid-Cretaceous thrust and June 2008 at 27 sites along the four major creeks and faulting and Tertiary displacement along the Darington-Devils their tributaries (pl. 1) to quantify surface water leaving the Mountain Fault Zone (DDMFZ; extends from northwest to tributary subbasins during low-flow conditions, and to identify southeast across the central part of the study area). Tertiary gaining and losing creek reaches. Streamflow measurements at vertical or oblique offset along the DDMFZ likely provided USGS gaging stations and synoptic sites were made by USGS the topographic relief necessary to produce the alluvial fan and personnel, assisted by Skagit County Public Works staff, braided stream deposits in the sedimentary units. The presence using Price pygmy or AA current velocity meters according of igneous rocks within fault-bounded blocks of the DDMFZ to standardized techniques of the USGS (Rantz, 1982). suggests that emplacement of these rocks was strongly Streamflow data from the Ecology gaging station on East Fork controlled by pre-existing strands of the DDMFZ. Evidence of Nookachamps Creek were obtained from the Washington Quaternary displacement along the DDMFZ and other faults State Department of Ecology (2009). The USGS rates the in the study area has not been widely documented. Dragovich accuracy of discharge measurements based on the equipment, and DeOme (2006) offer evidence of Holocene offset along 6 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington a mile-long portion of the main strand of the DDMFZ include wave-worn shell fragments. Nearshore deposits in located north of Lake McMurray. Surficial and subsurface estuarine or tidal flat environments are composed of loose or interpretations suggest a lack of Quaternary displacement soft, sand, silt, and clay with various admixtures of organic along faults else where in the study area (Dragovich and material. others, 2002; Dragovich and DeOme, 2006). Peat (Qp).—Soft fibrous to woody peat, muck, and Continental glaciers advanced into Skagit County organic silt accumulated in bogs and swamps of abandoned several times during the Pleistocene Epoch. This ice, part of channels, kettles, and shallow oxbow lakes or other the Cordilleran ice sheet, is known as the Puget Lobe. The depressions; commonly poorly stratified to unstratified. most recent period of glaciation, the Vashon Stade of Fraser Landslide deposits (Qls).—Landslide deposits glaciation, began about 17,000 years ago when the continental consisting of mostly poorly sorted, unstratified, soft to ice sheet in Canada expanded, and the Puget Lobe advanced cohesive diamicton composed of boulders, cobbles, and southward into western Skagit County, eventually covering gravel in a soft sand, silt, or clay matrix. Mode of origin the entire Puget Sound basin before halting and retreating. includes slump-earth flows, debris slumps or flows, and rock During the Everson Interstade, beginning about 13,500 years avalanches (talus) and also includes a few alluvial fan and ago, the climate warmed and the lobe wasted back allowing thick colluvial deposits. marine waters to enter the Puget Sound basin, which had been Lahar runout deposits (Qvl)—Lahar runout deposits depressed due to glacial isostatic loading. Marine inundation consisting of loose, well-sorted, massive to normally buoyed the retreating ice and produced marine and estuarine graded, medium to fine grained, volcanic sand. These conditions in the study area. Postglacial filling of the Skagit deposits are interpreted by Dragovich and others (2000) as River valley, which had been excavated by subglacial melt hyperconcentrated flood or lahar runout deposits, originating water, was accomplished through Holocene fluvial, estuarine, from a Glacier Peak eruptive event(s), that followed an and deltaic deposition, and volcanic lahar deposits originating ancestral channel of the Skagit River, and are preserved in the from Glacier Peak. lower Skagit River Valley within the study area. Unconsolidated deposits of glacial and interglacial Quaternary (Pleistocene) glacial and non-glacial deposits origin are present throughout the study area. A typical include: glacial sequence progresses from advance outwash, to till, Everson glaciomarine drift (Qgdme).—Glaciomarine to recessional outwash. Fluvial, lacustrine, bog and marsh drift deposits consisting of soft (when wet) to stiff (when dry) depositional environments were common during interglacial diamicton locally containing vertical jointing or desiccation periods. Beneath these unconsolidated deposits of varying cracks, and lenses or layers of loose outwash sand and gravel. thickness are bedrock units that are exposed in large parts of Dragovich and others (2002) identified two distinct facies: the glacial upland and within the mountains along the eastern (1) a clast-rich diamicton that is massive or crudely stratified margin of the study area. Descriptions of the unconsolidated and composed of clay, gravel, sand and silt, with abundant and bedrock units present in the study area are given below. dropstones, and (2) a silt- and clay-rich deposit that is massive or, less commonly, occurs as varved or laminated rhythmites and is composed of moderately to well-sorted silt, clay, and Geologic Units sand that lacks or contains only rare gravel, cobble, or boulder dropstones. The simplified geologic representation of the tributary Everson recessional outwash (Qgo ).—Terrestrial to subbasins developed for this study consists of 18 geologic e marine recessional and deltaic outwash deposits consisting units (table 1) that are described below and are shown on the of loose sand, gravel, with local concentrations of cobbles, surficial geologic map (pl. 1) constructed for this investigation. boulders, and lenses of silt. Recessional outwash deposits vary Quaternary (Holocene to latest Pleistocene) nonglacial from non-bedded to subhorizontal beds a few feet thick that deposits include: are crudely defined by variations in cobble, gravel, and sand Alluvium (Qa).—Alluvium consisting of active or content, and contain sedimentary structures indicative of a abandoned channel and overbank deposits associated with the fluvial braided-channel environment. Deltaic outwash deposits present and ancient Skagit River. Channel deposits typically are moderately to well-sorted, and beds typically are inches are coarse grained and consist of loose sand and gravel. to several feet thick. Dragovich and others (2002) identified Overbank deposits consist mostly of soft to stiff, stratified high-amplitude planar foreset beds, indicative of deltaic sand, silt, and clay and minor amounts of peat. Floodplain deposition in the study area. splay deposits are composed of sand and gravel and form Everson glaciomarine outwash (Qgom ).— subtle to distinct levees adjacent to or near the present Skagit e Glaciomarine outwash deposits consisting of loose gravel, River channels. Alluvial-fan deposits are composed of poorly sand, and silt, and occasional silt beds and laminated to varved sorted, massive to weakly stratified, soft to stiff, gravel, silt, silt-sand couplets. Average grain size is smaller in this unit and sand that are mostly of debris-flow or debris-torrent than in terrestrial or deltaic outwash (Qgo ). Interlayering origin. Beach deposits consist of loose, moderately to well- e with glaciomarine drift indicates submarine deposition for sorted sand and gravel along modern shorelines that locally most areas mapped as unit Qgome, although it may locally Hydrogeologic Framework 7

Table 1. Simplified geologic units defined in this study and correlation with previous investigations.

[Definitions of simplified geologic units defined in this study are shown on plate 1]

Simplified geologic Geologic units in Geologic units in Geologic units in Period Epoch units defined in Schuster (2000) Dragovich and others Dragovich and DeOme this study 1:100,000 (2002) 1:24,000 (2006) 1:24,000

Qa Qac Qas Qaf Qb Qf Qa af Qb Qn Qas Qasl Qaf Qa Qoa Qoa Qoas Qp Qp Qm Qp Qp

Qls Qls Qta Qls Qls Pleistocene

Holocene to latest Qvl Qvlk Qvl

Qgdme Qgdme Qgoc Qgdme Qgdmec Qgdmed Qgdme Qgle

Qgoe Qgo Qgog Qgos Qgoe Qgode Qgoge Qgike Qgode Qgose

Qgome Qgom Qgome Qgome Qgomee

Quaternary Qgtv Qgt Qgtv Qgtv

Qgav Qga Qgas Qgav Qgav

Qglv Qgat Qglv Qglv Pleistocene

Qco Qco Qco Qco ot ot ot oo oo oo

Qcw Qcw Qcw

OEcb OEcb OEnb OEcbs OEcbcg OEcbs OEcbcg Evr Evr Evr Evr Eib Tertiary to Eocene Oligocene Ecbc Ecc Ecb Ecc

Jph Jmv Jsh JTRmt d h s e Jmv Ju JT mc JT mv JMmt MZu MZmm Jmv Ju Ju Jhmc h h R t R t JTP t h h h h hl h Pzi Pigbdt Jurassic and Pennsylvanian

include terrestrial outwash deposits (Dragovich and others, deposits are moderately stratified to stratified, moderately 2002). Beach deposits of loose sand and gravel are included in to well sorted, thinly to very thickly bedded (subhorizontal this unit and are locally associated with topographic benches or cross-stratification), and contain sedimentary structures or subtle wave-cut terraces that reflect temporary beach indicative of fluvial deposition. Advance outwash commonly reworking of the substrate during isostatic emergence. is overlain by till along a sharp contact, and conformably

Vashon Till (Qgtv).—Till composed of non-stratified, overlies or is complexly interlayered with older glacial and unsorted, dense to very dense diamicton consisting of clay, nonglacial units where present. silt, sand, and gravel in various proportions, with scattered Glaciolacustrine and distal outwash deposits (Qglv).— cobbles and boulders and rare to locally common layers and Glaciolacustrine and distal outwash deposits of glacial and (or) lenses of sand and/or gravel. Vashon till commonly underlies nonglacial origin, composed of moderately dense to dense, glaciomarine drift in the western part of the study area, and well sorted, clay and silt that are very thinly to very thickly unconformably overlies bedrock, advance outwash, and less bedded, and contain varying amounts of sand and gravel, and commonly, older glacial and non-glacial units. locally contains thick beds of massive, clast-rich diamicton,

Vashon advance outwash (Qgav).—Advance outwash and scattered dropstones. Clay and silt deposits represent deposits of moderately to very dense, medium to coarse sand low-energy lacustrine and distal fluvial facies; diamicton and and gravel, with local silt and clay interbeds. Advance outwash dropstones likely resulted from iceberg melt-out. 8 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Olympia nonglacial deposits (Qco).—Olympia Jurassic to Pennsylvanian low-grade metamorphic rocks: nonglacial deposits composed of dense to very dense, well Metamorphic rocks (JTP).—Rocks of the Helena- sorted, sand, gravelly sand, silt, clay, and peat that are very Haystack melange and Trafton sequence are composed thinly to thickly bedded, with minor gravel and cobble gravel, of complex assemblages of faulted and folded low-grade and rare diamicton of probable mass-flow origin (Dragovich metasediments, metavolcanics, and meta-intrusives, formed and others, 2002). Organic material (logs or wood fragments) as a result of continental margin subduction during the Late is common and differentiates the Olympia from the overlying Jurassic or Early Cretaceous. The exhumation of these rocks glaciolacustrine and distal outwash deposits. Olympia deposits from the subduction zone was likely accomplished by mid- contain sedimentary structures indicative of a meandering Cretaceous thrust faulting; followed by Tertiary displacement river environment. along the DDMFZ (Tabor, 1994; Dragovich and others, 2002; Older till (ot).—Older till consisting of dense to very Dragovich and DeOme, 2006). dense diamicton composed of clay, silt, sand, and gravel in various proportions, with scattered cobbles and boulders; Hydrogeologic Units may locally include glaciomarine drift. Dragovich and others (2002) do not assign a formal geologic symbol to this unit, The geologic units defined for this study were grouped which indicates the tentative nature of the correlation with into hydrogeologic units, consisting of aquifers and confining deposits of the Possession Glaciation (60,000–80,000 yr B.P.). units (table 2) on the basis of lithologic (depositional facies, Older outwash (oo).—Older outwash consisting of grain size, and sorting) and hydrologic (hydraulic conductivity glacial or nonglacial deposits composed of sand and gravel and unit geometry) characteristics. The hydrogeologic with varying amounts of silt and clay. Dragovich and others units defined in this study are similar to those defined and (2002) do not assign a formal geologic symbol to this unit, used by other investigations in areas adjacent to this study which indicates the tentative nature of the correlation with (Thomas and others, 1997; Dragovich and Grisamer, 1998; deposits of the Possession Glaciation (60,000–80,000 yr B.P.). GeoEngineers, 2003). Whidbey nonglacial deposits (Qcw).—Whidbey An aquifer is saturated geologic material that is nonglacial deposits of sand with interbeds of silt, clay, and sufficiently permeable to yield water in significant quantities local gravel lenses; peat and wood are common. Hansen and to a well or spring, whereas a confining unit has low Mackin (1949) interpreted the depositional environment as permeability that restricts the movement of groundwater and slowly aggrading meandering streams and adjacent flood limits the usefulness of the unit as a water source. Unconfined plains. and confined aquifer conditions are present in the tributary Tertiary (Oligocene to Eocene) sedimentary and igneous subbasins groundwater system. Unconfined or “water-table” rocks include: conditions occur when the upper surface of the saturated zone Rocks of Bulson Creek (OEcb).—The rocks of Bulson is at atmospheric pressure and is free to rise and decline in Creek consist of a conglomerate and sandstone facies. The response to changes in groundwater recharge and discharge. conglomerate facies is composed of poorly to rarely well The position of the water table is represented by water levels indurated pebble and cobble conglomerate, and contains lesser in shallow wells. Confined or “artesian” conditions occur interbeds of pebbly sandstone, siltstone, and minor diamictite when an aquifer is overlain by a less permeable confining (debris flows), and coal. The sandstone facies is composed unit and the groundwater is under pressure greater than of sandstone with interbeds of pebbly sandstone, siltstone, atmospheric pressure. Water in a tightly cased well drilled into conglomerate, coal, and shale. Marcus (1981) concluded a confined aquifer will rise to a height corresponding to the that the conglomerate facies was deposited in an alluvial fan hydraulic head (the potentiometric surface) of the confined to braided river environment. Dragovich and others (2002) groundwater at that location. If the hydraulic head is sufficient suggest the sandstone facies was deposited in a nearshore or to raise the water above land surface, the well will flow and shallow marine environment. is called a flowing artesian well. The potentiometric surface Volcanic rocks (Evr).—Rhyolite, andesite, and basalt in a confined aquifer is analogous to the water table in an occur as pyroclastic ash flow tuffs, lava flows, domes, dikes, unconfined aquifer. It fluctuates in response to changes in sills, and breccias. Lahar deposits (sandstones, siltstones, and recharge and discharge, however, unlike the water table, the conglomerates) are locally interbedded with rhyolitic tuffs, potentiometric surface is higher in altitude than the top of the breccias, and very thin coal beds. Age and field relations confined aquifer. indicate that andesites are contemporaneous with deposition Glacial deposits generally are heterogeneous, and of the Bulson Creek sandstone facies (Dragovich and DeOme, although a glacial aquifer may be composed primarily of 2006). sand or gravel, it may locally contain varying amounts Chuckanut Formation (Ecbc).—The Chuckanut of clay or silt. Conversely, a confining layer composed Formation consists of alternating intervals of coarse-grained predominantly of silt or clay, may contain local lenses of (sandstone and minor conglomerate) and fine-grained coarse material. These small-scale variations in lithology may (mudstone, fine-grained sandstone, and siltstone) deposits. influence the occurrence and movement of groundwater at These upward-fining cycles have been interpreted to represent a scale that is likely too small to be adequately represented a river and adjacent flood-plain depositional environment by the hydrogeologic framework constructed for this (Johnson, 1982). Hydrogeologic Framework 9

Table 2. Hydrogeologic units defined in this study and correlation with geologic units defined in this study and previous investigations.

[Definitions for hydrogeologic units defined in this study are shown on plate 2]

Simplified Geologic units in Geologic units in Hydrogeologic units geologic units Geologic units in Period Epoch Dragovich and Dragovich and defined in this study defined in Schuster (2000) others (2002) DeOme (2006) this study

Qa Qac Qas Qaf af Qb Qn Qas Qasl Qago Qb Qf Qoa Qoas Qa Qoa Qgoge Qa Qvl Qgome Qaf Qvl Qgome Alluvial and recessional Qvlk Qgom Qgike Qgode Qgoe Qgomee Qgoe outwash aquifer Qgome Qgo Qgose Pleistocene

Holocene to Qgod Qgog Qgos e

Qm Qp Qls Qgdme Qgt Qp Qls Qta Qgdme Qp Qls Qgdme Qls Qgdme Qgtv Qgdmec Qgdmed Till confining unit Qgoc Qgt Qgle Qgtv Qgtv Qga

Advance outwash Qgav Qga Qgas Qgav Qgav aquifer Qgl Glaciolacustrine Qglv Qgat Qglv Qglv Quaternary and distal outwash confining unit Qco Pleistocene

Inter-glacial Qco Qco Qco Qco alluvial aquifer Qot Older till ot ot ot confining unit Qooa

Older outwash and oo Qcw Qcw oo Qcw oo alluvial aquifer

OEc OEc Ec OEc OEn Ec OEc OEc Ec OEc OEc Ec Sedimentary aquifer b bc b b c bs bcg b bs bcg c Tertiary Eocene Oligocene to

EJTP Jph Jmv Jsh d h s Evr Eib Jmv Ju Igneous and JTRmt JMmt Evr Jmv Ju Ju h h Evr JTP e t h h hl JT mc JT mv metamorphic MZu MZmm Jhmc R t R t h h h Pzi Tertiary to Tertiary

Pennsylvanian bedrock unit Pigbdt

study. Local-scale variability in the distribution of glacial glacier bed during ice recession (Booth, 1994; Dragovich and depositional facies often results in the formation of spatially others, 1994). This interpretation is supported by the absence discontinuous units of varying thickness. Therefore, most units of glacial and older non-glacial deposits in wells located are not aerially contiguous throughout the study area, and unit along the Skagit River valley, and similar interpretations thickness may vary considerably over short distances. Glacial from previous investigations (Dragovich and Grisamer, 1998; and older non-glacial deposits are interpreted as largely absent GeoEngineers, 2003). Infilling of the Skagit River valley was within the Skagit River valley to a depth of about 300 ft accomplished through the accumulation of Holocene fluvial, below sea level, likely due to removal by southward flowing estuarine, and deltaic deposits, and volcanic lahar deposits subglacial melt water, prior to subaerial exposure of the originating from Glacier Peak. 10 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Bog and marsh deposits (Qp) typically are thin (less Inter-glacial alluvial aquifer (Qco).—The inter-glacial than 10 ft), discontinuous, and have a small areal extent in alluvial aquifer is present in the subsurface along the northern the study area. These deposits likely have little influence on and western periphery of the glacial upland, and in a few the regional hydrologic system and are not designated as a isolated bodies in the upland interior (fig. 6). Surface exposures hydrogeologic unit in this study. Nine hydrogeologic units of the unit occur along the southern edge of the Skagit River are recognized in the study area (table 2 and pl. 2) and their valley. The unit consists primarily of sand, gravel, silt, and lithologic and hydrologic characteristics are described below. clay, with minor lenses of gravel and cobbles, and commonly Alluvial and recessional outwash aquifer (Qago).— thickness ranges from 10 to 50 ft; however, thicknesses exceed The alluvial and recessional outwash aquifer is present 100 ft in places. In most of the study area, the inter-glacial throughout the Skagit River valley (Qa and Qvl, pl. 1) and in alluvial aquifer is overlain by either the glaciolacustrine-distal outwash (Qgl) or till (Qgt) confining units, and groundwater discontinuous or isolated bodies in glacial upland areas (Qgoe occurs under confined conditions. Unconfined conditions occur and Qgome, pl. 1) (fig. 2). The aquifer consists of sand, gravel, and cobbles with minor lenses of silt and clay. Thicknesses in limited areas where the aquifer may not be fully saturated or of Qago typically range from 10 to 50 ft in upland areas, and where it is exposed at land surface. from 200 to 450 ft in the Skagit River valley. Groundwater Older till confining unit (Qot).—The presence of the in this aquifer is unconfined where it is not fully saturated older till confining unit in the subsurface along the western or exposed at land surface, however, confined conditions periphery of the glacial upland (fig. 7) is based on the are likely where it is fully saturated and overlain by the till identification of glacial till deposits in 12 wells, and subsurface confining unit (Qgt). geologic interpretations from Dragovich and others (2002). Till confining unit (Qgt).—The till confining unit is Deposits associated with the older till confining unit were present at land surface throughout the glacial upland area not identified in any of the other wells used in this study and as thin, discontinuous bodies in the mountains along the and substantial uncertainty exists about the actual extent eastern margin of the study area (fig. 3). This low-permeability and thickness of this unit in the remainder of the study area. unit is composed of marine and terrestrial glacial diamicton The potential presence of this unit in the subsurface along the northern periphery of the glaciated upland was inferred (Qgdme, and Qgtv) and poorly sorted landslide deposits (Qls). The till confining unit consists of various proportions of clay, based on the units occurrence in the sediments to the south (Dragovich and others, 2002), and the need to characterize silt, sand, gravel, cobbles, and boulders, with locally occurring areas of residual sediment thickness between the base of the sand and gravel lenses capable of providing water for domestic overlying inter-glacial alluvial aquifer and the underlying use. Thicknesses of Qgt vary widely, but generally range from top of bedrock. Limited well data indicate that thicknesses of 10 to 100 ft, and exceed 300 ft in places (fig. 3). Qot typically range from 10 to 20 ft, and locally exceed 50 ft. Advance Outwash Aquifer (Qga).—The advance This low-permeability unit is composed of terrestrial glacial outwash aquifer is present in the subsurface throughout diamicton consisting of various proportions of clay, silt, sand, large parts of the glacial upland (fig. 4). Surface exposures and gravel, with scattered cobbles, and boulders. of the unit are limited to a few steep slopes and along the Older outwash and alluvial aquifer (Qooa).—The walls of deeply incised stream valleys. The unit consists presence of the older outwash and alluvial aquifer in the mostly of sand and gravel with minor amounts of silt, and subsurface along the western periphery of the glacial upland scattered layers of pebble-cobble gravel and local silt and clay (fig. 8) is based on the identification of older outwash and interbeds. The thickness of Qga typically ranges from 10 to alluvial deposits in eight wells, and subsurface geologic 100 ft, but exceeds 200 ft in places. In most of the study area, interpretations from Dragovich and others (2002). Deposits groundwater in this aquifer is confined by the overlying till associated with the older outwash and alluvial aquifer were confining unit (Qgt), however, unconfined conditions may not identified in any of the other wells used in this study occur locally where it is not fully saturated or is exposed at and substantial uncertainty exists about the actual extent land surface. and thickness of this unit in the remainder of the study area. Glaciolacustrine and distal outwash confining unit The potential presence of this unit in the subsurface along (Qgl).—The glaciolacustrine and distal outwash confining the northern periphery of the glaciated upland was inferred unit is present in the subsurface throughout much of the based on the unit’s occurrence in the sediments to the south glacial upland in the northern part of the study area, and in (Dragovich and others, 2002), and the need to characterize discontinuous or isolated bodies in upland areas to the south areas of residual sediment thickness between the base of the (fig. 5). Surface exposures of the unit are limited to a few overlying older till confining unit and the underlying top of steep slopes and along the walls of deeply incised stream bedrock. The unit is composed of glacial (oo) and non-glacial valleys. This low-permeability unit consists of layers of clay (Qcw) alluvial deposits and consists primarily of sand, and and silt that contain varying amounts of sand and gravel with gravel, with varying amounts of silt and clay. Limited well data occasional diamicton and dropstones. The unit commonly indicate thicknesses of Qooa typically range from 50 to 100 ft, thickness ranges from 10 to 50 ft; however, thicknesses exceed and locally exceed 200 ft (fig. 8). Groundwater in this aquifer 100 ft in places. is confined by the overlying older till confining unit (Qot). Hydrogeologic Framework 11

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS EXPLANATION Extent and thickness of alluvial and recessional Bedrock outcrop outwash aquifer (Qago), in feet Boundary of tributary subbasin 0 – 50 101 – 200 301 – 450 Well used to determine extent and 51 – 100 201 – 300 thickness of aquifer—See plate 1

Figure 2. Extent and thickness of alluvial and recessional outwash aquifer (Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 02 12 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Extent and thickness of till confining Bedrock outcrop unit (Qgt), in feet Boundary of tributary subbasin 5 – 50 101 – 200 301 – 541 Well used to determine extent and 51 – 100 201 – 300 thickness of confining unit—See plate 1

Figure 3. Extent and thickness of till confining unit (Qgt) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 03 Hydrogeologic Framework 13

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS EXPLANATION Extent and thickness of advance outwash Bedrock outcrop aquifer (Qga), in feet Boundary of tributary subbasin 5 – 50 101 – 200 301 – 331 Well used to determine extent and 51 – 100 201 – 300 thickness of aquifer—See plate 1

Figure 4. Extent and thickness of advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 04 14 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Extent and thickness of glaciolacustrine and Bedrock outcrop distal outwash confining unit (Qgl), in feet Boundary of tributary subbasin 5 – 50 101 – 200 Well used to determine extent and 51 – 100 201 – 239 thickness of confining unit—See plate 1

Figure 5. Extent and thickness of glaciolacustrine and distal outwash confining unit (Qgl) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 05 Hydrogeologic Framework 15

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Extent and thickness of inter-glacial Bedrock outcrop alluvial aquifer (Qco), in feet Boundary of tributary subbasin 5 – 50 101 – 200 Well used to determine extent and 51 – 100 201 – 288 thickness of aquifer—See plate 1

Figure 6. Extent and thickness of inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 06 16 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Extent and thickness of older Bedrock outcrop till confining unit (Qot), in feet Boundary of tributary subbasin 5 – 50 101 – 200 Well used to determine extent and 51 – 100 thickness of confining unit—See plate 1

Figure 7. Extent and thickness of older till confining unit (Qot) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 07 Hydrogeologic Framework 17

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS EXPLANATION Extent and thickness of older outwash and Bedrock outcrop alluvial aquifer (Qooa), in feet Boundary of tributary subbasin 5 – 50 101 – 200 Well used to determine extent and 51 – 100 201 – 269 thickness of aquifer—See plate 1

Figure 8. Extent and thickness of older outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 08 18 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Sedimentary aquifer (OEc).—The sedimentary aquifer Q2.25 Tt crops out in large parts of the glacial upland and mountains = (1) s ln 2 , in central and southern portions of the study area, and also is 4πT rS present in the subsurface throughout this same area (fig. 9). The aquifer is largely absent in the mountains along the where eastern margin of the study area. The unit consists primarily s = drawdown in the well, in feet; of pebble and cobble conglomerate (OEc ), and medium- to b Q = discharge or pumping rate of the well, in cubic coarse-grained sandstone (OEcb and Ecbc), with fine-grained intervals of mudstone, siltstone, coal, and shale. Groundwater feet per day; in the sedimentary aquifer is unconfined where it crops out; T = transmissivity of the hydrogeologic unit, in however, confined conditions are likely where it is fully feet squared per day; saturated and overlain by glacial confining units. Fine-grained intervals within the aquifer also may produce locally confined t = length of time the well was pumped, in days, conditions. r = radius of the well, in feet; and Igneous and metamorphic bedrock unit (EJTP).—The S = storage coefficient, a dimensionless number, igneous and metamorphic bedrock unit crops out along the assumed to be 0.0001 for confined units northern margin of the glacial uplands in the mountains along the eastern margin of the study area, and within segments of and 0.1 for unconfined units. the DDMFZ (fig. 9). This low-permeability unit is composed of volcanic (Evr) and metamorphic rocks (JTP) and consists Assumptions for using equation 1 are that aquifers are of rhyolite, andesite, basalt, and complex assemblages of low- homogeneous, isotropic, and infinite in extent; wells fully grade metasediments, metavolcanics, and meta-intrusives, and penetrate the aquifer; flow to the well is horizontal; and water is considered to be non-water bearing except in localized areas is released instantaneously from storage. Additionally, for of fracturing. unconfined aquifers, drawdown is assumed to be small in relation to the saturated thickness of the aquifer. Although many of the assumptions are not precisely met, the field Hydraulic Conductivity conditions in the study area approximate most of the assumptions and the calculated hydraulic conductivities are Hydraulic conductivity is a measure of a material’s likely reasonable estimates. ability to transmit water, and hydraulic conductivity in A computer program was used to solve equation 1 for unconsolidated sediment is dependent on the size, shape, transmissivity (T) using Newton’s iterative method (Carnahan distribution, and packing of the particles. Because these and others, 1969). The difference in computed transmissivity physical characteristics vary greatly within the glacial deposits between using 0.1 and 0.0001 for the storage coefficient was a of the study area, hydraulic conductivity values also are factor of only about 2. Next, the following equation was used highly variable. Estimates of the magnitude and distribution to calculate horizontal hydraulic conductivity: of hydraulic conductivity were used to help understand groundwater movement and availability in the hydrogeologic T (2) units. Kh = , Horizontal hydraulic conductivity was estimated for the b hydrogeologic units using drawdown data from drillers’ logs that were observed after wells were pumped for a specified where period. Only data from those wells that had a drillers’ log Kh = horizontal hydraulic conductivity of the containing discharge rate, time of pumping, drawdown, static geologic material near the well opening, water level, well-construction data, and lithologic log were used. in feet per day; and Two different sets of equations were used to estimate b = thickness, in feet, approximated using the hydraulic conductivity, depending on well construction. length of the open interval as reported in For data from wells with a screened or perforated interval, the drillers' report. the modified Theis equation (Ferris and others, 1962) was first used to estimate transmissivity of the pumped interval. Transmissivity is the product of horizontal hydraulic The use of the length of a well’s open interval for b may conductivity and thickness of the part of the hydrogeologic overestimate values of Kh because the equations assume that unit supplying water to the well. The modified equation is all water flows horizontally within a layer of this thickness. Although some of the flow will be outside this region, the amount can be expected to be small because in most sedimentary deposits, vertical flow is inhibited by layering. Hydrogeologic Framework 19

122°20' 122°10' T. 35 N.

T. 34 N.

48°25'

T. 33 48°20' N.

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS EXPLANATION Extent of hydrogeologic bedrock units Bedrock at land surface Sedimentary aquifer (OEc) Boundary of tributary subbasin Igneous and metamorphic Fault bedrock unit (EJTP) Well used to determine extent of sedimentary aquifer and igneous and metamorphic bedrock unit—See plate 1

Figure 9. Extent of sedimentary aquifer (OEc) and igneous and metamorphic bedrock unit (EJTP) in tributary subbasins and vicinity, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 09 20 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

For data from wells having only an open end, a second Groundwater Movement equation was used to estimate hydraulic conductivities. Bear (1979) provides an equation for hemispherical flow to an This section describes the movement of groundwater in open-ended well just penetrating a hydrogeologic unit. When the aquifer system in the study area, and includes discussions modified for spherical flow to an open-ended well within a of recharge, flow direction, discharge, exchange of water unit, the equation becomes between the aquifer system and creeks, and temporal fluctuations in groundwater levels. These processes occur Q K = , (3) within the physical domain described by the hydrogeologic h 4π sr framework, and are influenced by the hydrogeologic characteristics of the aquifer system in which they occur, and This equation is based on the assumption that horizontal other factors, including streamflow, and the spatial distribution and vertical hydraulic conductivities are equal, which is not of precipitation and land cover. likely for the deposits in the study area. The result of violating this assumption probably is an underestimate of Kh by an Recharge unknown amount. Horizontal hydraulic conductivities were calculated for Precipitation is the dominant source of water recharging those wells with available data, and statistical summaries the groundwater system in the study area, and it is reasonable were prepared by hydrogeologic unit (table 3). The values of to expect variations in recharge to be related to spatial and estimated median hydraulic conductivity for the aquifers are temporal variations in precipitation. However, factors, such similar in magnitude to values reported by Freeze and Cherry as the permeability of surficial hydrogeologic units and (1979) for similar materials: Qago, 47 ft/d; Qga, 48 ft/d; Qco, land-cover characteristics, also affect recharge; therefore, the 57 ft/d: Qooa, 26 ft/d; and OEc, 0.27 ft/d (table 3). Estimated relation between precipitation and recharge is likely to vary median hydraulic conductivity for the confining units (Qgt, according to hydrogeologic and land-cover characteristics. 13 ft/d; Qgl, 26 ft/d; Qot, 11 ft/d) and bedrock unit (EJTP, The distribution of recharge from precipitation in the four 0.13 ft/d) are higher than is typical for most of the material tributary subbasins was estimated by applying precipitation- in these units because the available data for confining units recharge relations based on regression equations developed usually are from wells that are preferentially open to lenses for areas in Washington State (Bidlake and Payne, 2001) that of coarse material, or in the case of bedrock, where fractures incorporate the effects of surficial hydrogeology and tree exist. As a result, the data are biased toward the more canopy characteristics. The effects of impervious surfaces productive zones in these units and are not representative of on the distribution of recharge from precipitation also were the entire unit. estimated in the study area.

Table 3. Statistical summary of hydraulic conductivity values by hydrogeologic unit in tributary subbasins and vicinity, lower Skagit River basin, Washington.

[–. no data]

Number Hydraulic conductivity (feet per day) Hydrogeologic unit of wells Minimum Median Maximum Qago Alluvial and recessional outwash aquifer 13 0.04 47 1,322 Qgt Till confining unit 4 6.7 13 89 Qga Advance outwash aquifer 30 2.6 48 722 Qgl Glaciolacustrine and distal outwash confining unit 1 – 126 – Qco Inter-glacial alluvial aquifer 8 1.4 57 393 Qot Older till confining unit 1 – 111 – Qooa Older outwash and alluvial aquifer 1 – 126 – OEc Sedimentary aquifer 16 .05 .27 20 EJTP Igneous and metamorphic bedrock unit 5 .04 .13 40 1Single measurement values represented as median. Groundwater Movement 21

Average annual precipitation totals were calculated plots mid-way between these unconsolidated units (fig. 11). from daily values for the study period (September 1, 2006, Recharge characteristics of the bedrock unit were estimated to August 31, 2008), obtained from the National Climate to be less than the unconsolidated confining units, and a Data Center, NCDC, (www.ncdc.noaa.gov), for three active precipitation-recharge relation was selected for the bedrock National Weather Service (NWS) stations near the study unit that represents one-half the recharge of the unconsolidated area: Sedro-Woolley (NWS station 457507), Arlington (NWS confining units. station 450257), and Anacortes (NWS station 450176). The effect of evaporative loss associated with the These point data were extrapolated across the study area interception of precipitation by tree canopy on recharge from based on the spatial distribution of normal precipitation precipitation (fig. 11) was estimated for unconsolidated and (average annual precipitation for 1971–2000) provided by bedrock aquifers using equations from Bidlake and Payne the computer­ program Parameter-elevation Regressions on (2001), and tree canopy distribution data obtained from the Indepen­dent Slopes Model, PRISM, (Daly and others, 1994; National Land Cover Database, NLCD (2001). Interception Oregon State University, 2009). The PRISM model estimates loss was applied to areas with more than 50 percent tree the distribution of normal annual precipitation based on a canopy (fig. 10). Urban centers in the study area manage storm statistical method that takes into account altitude and spatial water by discharging runoff to rivers or streams rather than variation. by infiltrating to groundwater, therefore, recharge within city Normal annual precipitation at each NWS station was limits was reduced according to the percentage of impervious obtained by sampling the PRISM distribution at the three surface (figs. 10 and 12) derived from the National Land station locations; allowing the PRISM distribution to be scaled Cover Database (2001). No direct recharge from precipitation for extrapolation. The normal precipitation was compared was assumed for areas covered by lakes. to the average annual precipitation for the study period GIS techniques were used to combine the data coverages (September 1, 2006, to August 31, 2008) at the NWS stations described above, and calculate the distribution of groundwater and a regression equation was developed for the three points: recharge from precipitation at a 1,000 ft cell size in the four tributary subbasins (fig. 13). Recharge rates range from less

Pactual = 4.35 in/yr + 0.911 × Pnormal than1 in/yr in urban areas underlain by impervious surfaces to about 46 in/yr in mountainous terrain underlain by till deposits This relation was used to estimate the distribution of average with less than 50 percent tree canopy along the eastern annual precipitation for the study period throughout the margin of East Fork Nookachamps Creek subbasin where study area (fig. 10), based on the PRISM distribution of precipitation locally exceeds 120 in/yr. Summing the recharge normal precipitation. The tributary subbasins received about areas shown in figure 13 indicates that the groundwater system 284,000 acre-ft or about 56 in. of precipitation during an within the subbasins receives about 92,400 acre-ft or about average year (September 1, 2006, to August 31, 2008). 18 in. of recharge from precipitation during an average year Precipitation during an average year for each subbasin (September 1, 2006, to August 31, 2008). The calculated was: East Fork Nookachamps Creek, 136,920 acre-ft recharge from precipitation during an average year for each (70 in/yr); Nookachamps Creek, 74,820 acre-ft (49 in/yr); subbasin was: East Fork Nookachamps Creek, 41,060 acre-ft Carpenter Creek, 46,610 acre-ft (46 in/yr); and Fisher Creek, (21 in/yr); Nookachamps Creek, 23,840 acre-ft (16 in/yr); 25,730 acre-ft (47 in/yr). Carpenter Creek, 17,200 acre-ft (17 in/yr); and Fisher Creek, The effects of surficial hydrogeology on the distribution 10,300 acre-ft (19 in/yr). of recharge from precipitation (fig. 11) were estimated based Precipitation-recharge relations developed by Bidlake on regression equations developed by Bidlake and Payne and Payne (2001) included only annual precipitation as much (2001) for soils in western Washington formed on glacial as 60 in/yr, whereas, areas along the eastern boundary of the outwash and alluvial sediments, and soils formed on glacial tributary subbasins locally receive greater than 120 in/yr. till and fine-grained sediments. Recharge estimates for aquifer To estimate recharge for areas receiving between 60 and units (outwash and alluvium) exposed at land surface in the 120 in. of annual precipitation, regression equation lines were study area were based on the regression equation developed extended using a constant slope from 60 to 120 in/yr. The for soils formed on glacial outwash and alluvial sediments; upper limits of the precipitation-recharge relation are poorly recharge estimates for confining units (till and lacustrine) understood and a reduction in the efficiency of groundwater were based on the regression equation developed for soils recharge from precipitation likely takes place at some point, formed on glacial till and fine-grained sediments. Recharge resulting in the potential for over estimation of recharge estimates for areas where sedimentary and bedrock units (William Bidlake, U.S. Geological Survey, oral commun., are exposed at land surface required the approximation of 2009). additional precipitation-recharge equations for this study that In addition to groundwater recharge from precipitation, were based on a qualitative comparison of the hydrogeologic groundwater recharge from creeks also occurs in the properties of unconsolidated, sedimentary, and bedrock units. study area along losing creek reaches. The total amount Recharge characteristics of the sedimentary aquifer were of groundwater recharge from creeks was not quantified, estimated to be less than unconsolidated aquifers and greater but this total is reflected in the computation of the total net than unconsolidated confining units, and a precipitation- groundwater discharge to creeks used in the water budget. recharge relation was selected for the sedimentary aquifer that 22 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. Sedro- 35 Skagit

Woolley River N.

Burlington N o o 60 k a Clear ch am Lake ps C Barney r 80 e e Lake k Cr git Ri r eek ka ver Beaver e S Eas rn t Lake Tu 100

undt M C 120 F r ee o k

r k T. Mount N o 34 o k Vernon a N. c h a N m o 48°25' p o s k a c

h k e a e m r p C C s r

e

e

k

W C a a r lk p e e r rk o n F

t

e h e

t v r r

i

r

R o N t Big i g C ka r ee Lake C S k re

ek

Ten See figure 12 for detail

S Lake andy C r e ek Devils

40 Lake Johnson C 60 80 r re

e ek v

i k

R e Sixteen

e

r

C Bu

ls Lake

on

t r i T. k

e g C e

t re a e n e

k r 33 k e

p C S r N. 48°20' k a e e r C e C

k k

r a o L k F c u Lake h lc h McMurray i t P u F

o i S s c h e r

SKAGIT COUNTY

Skagit C reek SNOHOMISH COUNTY

A Bay r Lake m 80 s t r Ketchum o n g

C r 60 e

e T. Stanwood k 32 N. R. 3 E. R. 4 E. R. 5 E. R. 6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 43210 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS EXPLANATION Canopy cover, in percent Impervious surface Less than 50 percent Represents all percentages. More than 50 percent See figure 12 for detail 60 Line of equal average annual precipitation. Interval is 20 inches Boundary of tributary subbasin

Figure 10. Average annual precipitation, canopy cover, and impervious surface across the tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 10 Hydrogeologic Framework 23

120

Recharge as a function of surficial hydrogeology Unconsolidated aquifers (Qago, Qga, Qco, and Qooa) Without trees With trees 100 Sedimentary aquifer (OEc) Without trees With trees Unconsolidated confining units (Qgt, Qgl, and Qot) Igneous and metamorphic bedrock unit (EJTP) 80

60 RECHARGE, IN INCHES PER YEAR 40

20

0 0 20 40 60 80 100 120 140 PRECIPITATION, IN INCHES PER YEAR

Figure 11. Precipitation-recharge relations used in this study, lower Skagit River basin, Washington.

tac09-9722-0328 Upper Skagit Geo_Fig 11 24 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10'

SR SR T. I 20 Sedro- 9 35 5 Skagit Woolley N. River

Burlington N o

o k a Clear ch am Lake ps C SR r 20 e e ee Barney k r k C it R Lake r ag ive Beaver e k r E n S as Lake r t Tu SR 536

F SR o r T. 538 k 34

N N. Mount o o k 60 Vernon a c h a N m o 48°25' p o 80 s k a c

h k e a e m r p C C s r

e

e

k

40 Fork

River h t or N it I SR Big T. ag 5 9 k Lake 33 S N. R. 3 E. R. 4 E. R. 5 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 0 1 2 3 4 MILES Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 3210 4 KILOMETERS National Land-Cover Database, 2001 EXPLANATION Canopy cover, in percent Impervious surface, in percent 60 Line of equal average annual precipitation. Interval Less than 50 percent Less than 20 percent is 20 inches More than 50 percent 21 – 40 Boundary of tributary subbasin 41 – 60

61 – 80 More than 80 percent

Figure 12. Detail of distribution of impervious surfaces in tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 12 Hydrogeologic Framework 25

122°20' 122°10' T. Sedro- 35 Skagit Woolley River N.

N

o

o Burlington k a Clear ch am Lake ps C r e Barney e k C Lake r git Ri r eek ka ver Beaver e S Eas rn t Lake Tu

undt M C F r ee o k

Mount r k T.

Vernon N o 34 o k a N. c h a N m o 48°25' p o s k a c

h k e a e m r p C C s r

e

e

k

W C a a r lk p e e r rk o n F

t

e h r

t e r

r v

i o N R Big

C it r g ee Lake C a k r ee

k k

S

Ten

S Lake andy C r e ek Devils Johnson Lake C r re

e ek v

i k

R e Sixteen

e

r

C Bu

ls Lake

on

t r i T. k

e g C e

t re a e n e

k r 33 k e

p C S r N. 48°20' k a e e r C e C

k k

r a o L k F c u Lake h lc h McMurray i t P u F

o i S s h er

SKAGIT COUNTY

Skagit Cr eek SNOHOMISH COUNTY Bay Lake Ketchum

T. Stanwood 32 N. R. 3 E. R. 4 E. R. 5 E. R. 6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 43210 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION 43210 5 KILOMETERS Average annual groundwater recharge, in inches per year 0 – 11.50 26.51 – 30.50 11.51 – 19.50 30.51 – 46.36 19.51 – 26.50 Boundary of tributary subbasin

Figure 13. Distribution of average annual groundwater recharge from precipitation in tributary subbasins and vicinity, lower Skagit River basin, Washington, September 2006–August 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 13 26 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Groundwater-Flow Directions southern part of the study area (figs. 16 and 17, respectively). Widely spaced water-level data in the northern part of the The direction of horizontal groundwater flow can be area suggest a northwestward and southeastward direction of inferred from contour maps of water-level altitudes. The groundwater flow in the inter-glacial alluvial aquifer (Qco). direction of groundwater flow generally is from areas of Directions of groundwater flow in the sedimentary recharge to areas of discharge in the direction of decreasing aquifer (OEc) likely reflect both local and regional flow water-level altitudes and perpendicular to the water-level patterns (fig. 18). Recharge to the sedimentary aquifer (OEc) altitude contours. Groundwater levels measured monthly aquifer preferentially occurs in mountainous areas where the (October 2006 through September 2008) were used to infer unit is exposed at land surface (figs. 9 and 13). Water-level direction of groundwater flow in study area aquifers figs.( 14 altitudes in these areas reflect local topographic relief fig.( 18) through 18). The mean water-level value for October 2006 and suggest radial flow from bedrock highs down beneath the through September 2008 was used to represent the water- surrounding unconsolidated sediments. Westward groundwater level altitude at monitoring wells measured monthly for this flow in the sedimentary aquifer (OEc) occurs along the analysis. Synoptic groundwater levels measured during the mountain front in the eastern part of the study area, and is field inventory (August through October 2006) were used only coincident with a regional westward decrease in land-surface in areas where monthly water-level data were not available, altitude from the mountains to the Puget Sound. and in places field inventory values do not correlate well with Vertical gradients and flow in the groundwater system water-level altitude contours based on monthly data. Water- are difficult to determine because extents and thicknesses level contours for most aquifer units are based on limited of hydrogeologic units vary considerably throughout the water-level data, and are subject to some uncertainty. Water- study area, the presence of confining units within and level contours were not drawn for the alluvial and recessional between aquifers is highly variable, and water-level data for outwash aquifer (Qago) because of the discontinuous nature comparison between adjacent units are widely spaced. Water- of the unit within the tributary subbasins. Water-level contours level altitude differences between the advance outwash (Qga) also were not drawn for large parts of the advance outwash and inter-glacial alluvial (Qco) aquifers in the southwestern (Qga), inter-glacial alluvial (Qco), and older outwash and part of the study area, where sufficient contoured data were alluvial (Qooa) aquifers due to limited water-level data for available to make a comparison, suggest downward vertical these units. flow (figs. 15 and 16). Groundwater flow in the Qago aquifer likely follows The potential for upward groundwater movement, the land-surface gradient, with water generally moving in a indicated by the presence of flowing wells, was observed at northwesterly direction from high-altitude areas in the upper several locations within the aquifer units. Confining clays portions of the tributary subbasins towards the Skagit River within the alluvial and recessional outwash aquifer (Qago) and Puget Sound (fig. 14). This generalized flow pattern likely produce intermittent flowing conditions observed at is likely complicated by the presence of large areas of low two wells along the eastern margin of the Skagit River valley permeability glacial till (Qgt) that separate discontinuous (fig. 14). Upward flow in the advance outwash (Qga) aquifer is bodies of Qago and act as local groundwater-flow barriers. suggested by the presence of three continuously flowing wells In the southern part of the study area, groundwater flow near Big Lake, and two intermittent flowing wells located in the advance outwash aquifer (Qga) is towards the west in along the mountain front (fig. 15). Confined groundwater the direction of the Skagit River and Puget Sound (fig. 15). conditions are attributed to the presence of overlying till North to northwestward groundwater flows beneath major deposits (Qtv) at both of these locations. A continuously tributary river valleys, and localized radial flow are inferred flowing well completed in the older outwash and alluvial from widely spaced water-level data in central and northern aquifer (Qooa) indicates the potential for upward flow in parts of the area. the southwestern part of the study area (fig. 17), and upward Groundwater flow in the inter-glacial alluvial (Qco) and flow in the sedimentary aquifer (OEc) is indicated by an older outwash and alluvial (Qooa) aquifers is towards the west intermittent flowing well adjacent to Lake McMurray fig.( 18). in the direction of the Skagit River and Puget Sound in the Groundwater Movement 27

122°20' 122°10' T. 35 Skagit r Rive N. 35D01 29

N

oo

k 01A02 ac 36 Clear ha mp Lake s 11C01 08A01 C r 28 713 e e k Barney Beaver Cr git Ri r eek ka ver Lake Lake e S Ea n st ur T

17D01 t Mund C 15 11Q01 r ee 57 k

F

o N 23A01 r T. o k o 202 k 34 a 20E01 c N. h 23R01 a 220

m

132 p 48°25' s N 20N01 eek o 88 r o C

k a c C hamps r e

e

k

34E01 W

221 a l r k e te r Fork n e h p t r C r a

o r River C

N t e i 06B01 e g 04C01 k Big k a 7 S 39 04F01 Lake Cre 05M01 32 F ek 7 Ten Lake k S e an e dy r C 08D01 r

C 6 e

ek 08R01 Devils

11 F Jo Lake hn s 17D01 on

C r r

eek 125 e

v

i

R Sixteen

r

te

n B

e ul Lake so

p n

t r k i

a e g C T.

re e a C e

k r k 33 C k e

S e

r N. 48°20' C 20F01

e

65 26B01 k k 20J01 a r L o 293 k F 197 c u h lc h Lake i t P u McMurray o

S

F

i s he

r ek Cre Skagit Bay 05G01 227 Lake Ketchum 05G02 233

T. 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or 0 1 2 3 4 5 MILES Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Alluvial and recessional outwash aquifer (Qago) Measurement location and water-level altitude, in feet above North American Vertical Datum of 1988 (NAVD 88) Inferred direction of groundwater flow 05G02 Well used to measure water-level altitudes on a monthly basis— Boundary of tributary subbasin 233 The mean water-level altitude for October 2006 through September 2008 was used to represent the water-level altitude at each of the wells monitored on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom) 08D01 Field inventory well used to measure synoptic water-level altitudes— 6 Synoptic water-level altitude for August through October 2006 was used only in areas where monthly water-level data were not available. Numbers are well No. (top) and water-level altitude (bottom) F Flowing well

Figure 14. Water-level altitudes and direction of groundwater flow in alluvial and recessional outwash aquifer (Qago) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008. tac09-9722-0328 Upper Skagit Geo_Fig 14 28 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 Skagit r Rive N.

N

oo

k ac Clear ha mp Lake s C r e

Barney e k Cr git Ri r eek ka ver Lake Beaver e S ast n E Lake ur T 13M01 123 09R01 14J01 Mundt 18A01 C 140 F r 49 o ee k r 98 k

N T. o 23A02 19M01 14R01 o k 156 34 166 a 241 c N. h

a m N p 48°25' 23N01 s 25B01 o o 208 160 19K01 k 23N02 a k 176 F c e 204 h e a r C mps C r

e

e

k

C W a 36M01 a r lk 32L01 p e e 120 F r For k n 8 05C01 h 01A01 t t e r 234 F

o r 115

River

N t i Big g C Sk a ree Lake C k reek 04N01 Ten 06D01 -9 S Lake 118 F andy 07B01 C r 83 e ek Devils Johns Lake on Cr

r ee 18A01

e 17J01 k

v i k 148 F

-14 Sixteen k

R e

e e

r e

Bu

C ls Lake r

on

C

t r i

e C g t r T.

ee a n k

e k e 33 p 20Q01 21N01 k k S r e 48°20' N. a 86 a e 110 r L C C

29B01 28K01 25J01 k r 254 30D01 o 84 233 k F 235 c u 100 h lc h 29J01 F Lake i t ish 28K02 P u 106 McMurray o e 300 S r 25Q01 29Q01

237 105

34L01 31D02 300 329

236

33F01 34L02

279 331

200

04H01 k Skagit 275 Cr ee 100 A Bay r Lake m s 04N01 t r Ketchum o 253 n 05Q03 g

88 05Q02

107 C r e T. 05Q02 e k 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or 0 1 2 3 4 5 MILES Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Measurement location and water-level altitude, in feet above North American Vertical Datum of 1988 (NAVD 88) Advance outwash aquifer (Qga) 04N01 Well used to measure water-level altitudes on a monthly basis— Approximate water-level contour—Shows altitude of 253 The mean water-level altitude for October 2006 through September 2008 water level in advance outwash aquifer, October was used to represent the water-level altitude at each of the wells monitored 2006–September 2008. Contour interval, 100 feet. on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom) Datum is North American Vertical Datum of 1988 05Q02 Field inventory well used to measure synoptic water-level altitudes— (NAVD 88) 107 Synoptic water-level altitude for August through October 2006 was used only in Boundary of tributary subbasin areas where monthly water-level data were not available. Numbers are well No. (top) and water-level altitude (bottom) Inferred direction of groundwater flow F Flowing well

Figure 15. Water-level altitudes and direction of groundwater flow in advance outwash aquifer (Qga) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 15 Groundwater Movement 29

122°20' 122°10' T. 35 Skagit r Rive N.

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oo k Clear ac ha Lake mp s C r e

e k Barney Cr git Ri r eek ka ver Lake e S t n as Beaver ur E T

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r e T. e k 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or 0 1 2 3 4 5 MILES Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Measurement location and water-level altitude, in feet above North Inter-glacial alluvial aquifer (Qco) American Vertical Datum of 1988 (NAVD 88) 28M01 Well used to measure water-level altitudes on a monthly basis— Approximate water-level contour—Shows altitude of water 108 The mean water-level altitude for October 2006 through September 2008 level in inter-glacial alluvial aquifer, October 2006–September 2008. was used to represent the water-level altitude at each of the wells monitored Contour interval, 100 feet. Datum is North American on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom) Vertical Datum of 1988 (NAVD 88) 32D02 Field inventory well used to measure synoptic water-level altitudes— Boundary of tributary subbasins 81 Synoptic water-level altitude for August through October 2006 was used only in areas where monthly water-level data were not available. Numbers are well No. (top) Inferred direction of groundwater flow and water-level altitude (bottom)

Figure 16. Water-level altitudes and direction of groundwater flow in inter-glacial alluvial aquifer (Qco) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008. tac09-9722-0328 Upper Skagit Geo_Fig 16 30 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 Skagit r Rive N.

N oo Clear k ac Lake ha mp s C r e

Barney e k Cr git Ri Lake r eek ka ver Beaver e S E n as Lake ur t T

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r e T. e k 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or 0 1 2 3 4 5 MILES Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) EXPLANATION Measurement location and water-level altitude, in feet above North American Vertical Datum of 1988 (NAVD 88) Older outwash and alluvial aquifer (Qooa) 33G01 Well used to measure water-level altitudes on a monthly basis— Approximate water-level contour—Shows altitude of water level in 110 The mean water-level altitude for October 2006 through September 2008 older outwash and alluvial aquifer, October 2006– was used to represent the water-level altitude at each of the wells monitored September 2008. Contour interval, 50 feet. Datum is on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom) North American Vertical Datum of 1988 (NAVD 88) 04N04 Field inventory well used to measure synoptic water-level altitudes— Boundary of tributary subbasin 147 Synoptic water-level altitude for August through October 2006 was used only in areas where monthly water-level data were not available. Numbers are well No. (top) Inferred direction of groundwater flow and water-level altitude (bottom) F Flowing well

Figure 17. Water-level altitudes and direction of groundwater flow in older outwash and alluvial aquifer (Qooa) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 17 Groundwater Movement 31

122°20' 122°10' T. 35 Skagit r Rive N.

35D01

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k ac Clear ha Lake mp s C r e

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r e T. e k 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or 0 1 2 3 4 5 MILES Washington Division of Geology and Earth Resources digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 43210 5 KILOMETERS Horizontal Datum: North American Datum of 1927 (NAD 27) Measurement location and water-level altitude, in feet above North EXPLANATION American Vertical Datum of 1988 (NAVD 88) Sedimentary aquifer (OEc) 03G01 Well used to measure water-level altitudes on a monthly basis— 380 The mean water-level altitude for October 2006 through September 2008 Approximate water-level contour—Shows altitude of water level in was used to represent the water-level altitude at each of the wells monitored sedimentary aquifer, October 2006– September 2008. on a monthly basis. Numbers are well No. (top) and water-level altitude (bottom) Contour interval, 50 feet. Datum is North American Vertical Datum of 1988 (NAVD 88) 03A01 Field inventory well used to measure synoptic water-level altitudes— 295 Synoptic water-level altitude for August through October 2006 was used only in Boundary of tributary subbasin areas where monthly water-level data were not available. Numbers are well No. (top) Inferred direction of groundwater flow and water-level altitude (bottom) F Flowing well

Figure 18. Water-level altitudes and direction of groundwater flow in the sedimentary aquifer (OEc) in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2006–September 2008. tac09-9722-0328 Upper Skagit Geo_Fig 18 32 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Discharge discharged to creeks measured during August 2007, and approximately 129.6 ft3/s (93,830 acre-ft/yr) of groundwater Groundwater in the study area discharges as seepage to discharged to creeks measured during June 2008 (table 4). streams, lakes, springs, and marshes; as evapotranspiration of These data reflect seasonal variability in groundwater shallow groundwater; as submarine seepage to Puget Sound; discharge to creeks, however, much of the likely annual and as withdrawals from wells. Groundwater discharge variation in discharge (dryer and wetter conditions) is not sustains the late-summer and early-fall streamflow (baseflow) represented by these data. Many small streams were not of creeks in the study area. Estimates of groundwater measured, but they may collectively receive a significant discharge to creeks in the tributary subbasins were based on quantity of groundwater discharge at times throughout the synoptic streamflow measurements made in August 2007 and year. The time averaged (mean of the 2007 and 2008 discharge June 2008 at seven locations (table 4 and pl. 1); a streamflow measurements) area weighted groundwater discharge for the measurement for Carpenter Creek obtained from Pitz and entire tributary subbasin area was estimated to be 83.43 ft3/s Garrigues (2000); and estimates of evaporative loss from lakes (60,400 acre-ft/yr). This value includes area-weighted within measured reaches (National Oceanic and Atmospheric estimates of groundwater discharge for portions of subbasins Administration, 1982). Estimates of daily evaporative loss that were downstream of synoptic measurement sites. from lakes were used to account for losses in baseflow Area weighting values (measured discharge divided by the during synoptic streamflow measurements (August 2007 and contributing area upstream of the measurement site) were June 2008). These estimates were based on maps of annual derived for each of the tributary subbasins to better represent evaporation for shallow lakes near the study area (National spatial variation in groundwater discharge characteristics. Oceanic and Atmospheric Administration, 1982). Maps were The use of a time averaged groundwater discharge estimate developed using data from Class A pan evaporation stations to compute the area weighted groundwater discharge in the and other spatially distributed meteorological data for 1956– study area may not accurately represent the total annual 70. The accuracy of the maps is a function of the number of variation in discharge, and likely introduces some error into nearby data stations and their proximity to the area of interest; this calculation. The time averaged (period of record for each the closest stations are located in the southern Puget Sound streamflow-gaging station), area-weighted streamflow for the area. Estimates of annual evaporation assume long-term entire tributary subbasin area was estimated to be 221.8 ft3/s thermal stability of lake water. Daily values of evaporation (160,600 acre-ft/yr). were estimated using the average monthly percentage of Groundwater withdrawals from wells in the tributary annual evaporation derived from Class A pan evaporation data subbasins in 2008 were an estimated 2,200 acre-ft. This (National Oceanic and Atmospheric Administration, 1982) for quantity represents gross withdrawals (public-water supply, 1956–70. domestic use, and crop irrigation) and does not reflect Precipitation totals at Sedro-Woolley for June, July, the quantity of water returned to the groundwater system and August 2007 were 2.48, 1.31, and 1.24 in., respectively through septic tanks or through irrigation-return flows to (Western Regional Climate Center, 2008). The normal shallow aquifers. Public supply and domestic groundwater (average annual precipitation for the period 1971-2000) withdrawals were estimated using a typical water-use rate of precipitation at Sedro-Woolley for these months is 2.85, 228 gal/d per connection. The typical use rate was estimated 1.77, and 1.62 in. (National Oceanic and Atmospheric by multiplying a per-capita water-use rate of 84 gal/d (Lane, Administration, 2007). Precipitation totals at Sedro-Woolley 2009) by an estimate of 2.71 people per connection (U.S. for April, May, and June 2008 were 4.40, 2.97, and 3.13 in., Census Bureau, 2000). The number of connections within the respectively (Western Regional Climate Center, 2008). The tributary subbasins area was estimated using the Skagit and normal precipitation (average precipitation for selected months Snohomish Counties assessor database, and the Washington for the period 1971–2000) at Sedro-Woolley for these months State Department of Health database (Skagit County, 2008; is 3.76, 3.03, and 2.85 in. (National Oceanic and Atmospheric Snohomish County, 2008; Washington State Department of Administration, 2007). Health, 2008). Crop irrigation withdrawals were estimated by Groundwater discharge estimates represent flow from multiplying crop specific application rates by the number of contributing areas upstream of the synoptic streamflow- acres under production within the tributary subbasins for each measurement sites (57.7 mi2 ) and do not include contributing crop type, and then accounting for irrigation method efficiency areas in downstream parts of the subbasins (36.6 mi2). A total (U.S. Department of Agriculture, 2007; Washington State net of about 13.15 ft3/s (9,520 acre-ft/yr) of groundwater Department of Agriculture, 2008). Groundwater Movement 33

Table 4. Synoptic streamflow measurements used to determine groundwater discharge and estimates of evaporative loss from lakes in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2007 and June 2008.

[Measurement site: Site locations are shown in figure 22. Accuracy rating of U.S. Geological Survey measurements: F, fair; P, poor; estimated values are rated poor. ft3/s, cubic feet per second]

Date discharge Discharge Accuracy Measurement site Site No. measured (ft3/s) rating East Fork Nookachamps Creek subbasin Inflow to Beaver Lake 12200022 08-07-07 0.19 F 06-19-08 3.11 F Turner Creek 12200015 08-07-07 0.50 F 06-18-08 2.48 F East Fork Nookachamps Creek 12200010 08-07-07 4.58 F 06-19-08 66.1 F Nookachamps Creek subbasin Nookachamps Creek 12199600 08-09-07 0.76 F 06-19-08 33.1 F Carpenter Creek subbasin Carpenter Creek 12200696 09-21-00 12.22 F 06-19-08 12.4 F Fisher Creek subbasin Fisher Creek 12200701 08-07-07 0.49 P 06-05-08 6.38 F Tributary to Fisher Creek 1220070140 08-07-07 20.01 P 06-18-08 22.00 P Evaporative loss from lakes Evaporative loss from Big Lake August 2007 33.15 June 2008 32.85 Evaporative loss from Lake McMurray August 2007 30.97 June 2008 30.88 Evaporative loss from Sixteen Lake August 2007 30.28 June 2008 30.25 Total net measured streamflow August 2007 13.15 June 2008 129.6 1 Streamflow measured on September 21, 2000; accuracy rating assumed to be fair (Pitz and Garrigues, 2000); backwater conditions observed by U.S. Geological Survey on August 8, 2007. 2 Estimated by U.S. Geological Survey. 3 Calculated daily evaporative loss derived from National Oceanic and Atmospheric Administration (1982) annual values. 34 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Groundwater/Surface-Water Interactions was computed by subtracting the error-adjusted maximum value for inflow to Walker Creek (1.13 ft3/s) from the error- Characterization of the exchange of water between the adjusted minimum value for flow at Walker Creek (0.99 ft3/s) groundwater system and creeks in the study area was based on to determine the lower uncertainty value (0.99 ft3/s – synoptic streamflow measurements made in August 2007 and 1.13 ft3/s = -0.14 ft3/s). The upper uncertainty value was June 2008 at 27 creek locations and an Ecology streamflow- computed by subtracting the error-adjusted minimum value gaging station on East Fork Nookachamps Creek (table 5 and for inflow to Walker Creek from the error-adjusted maximum pl. 1); streamflow data for Carpenter Creek from Pitz and value for flow at Walker Creek (1.17 ft3/s – 0.95 ft3/s = Garrigues (2000); and estimates of evaporative loss from lakes 0.22 ft3/s). The uncertainty range suggests the possibility of (National Oceanic and Atmospheric Administration, 1982). either a gaining or losing creek reach, and does not support This information was used to identify stream reaches that the delineation of a gaining reach indicated by the unadjusted either gain flow from or lose flow to the shallow groundwater value of 0.04 ft3/s. Conclusions regarding delineation of system. August 2007 streamflow measurements were made gaining or losing creek reaches were able to be made at most during the low-flow season, usually July–August (fig. 19), locations (table 5). For example: the June 2008 error-adjusted to capture baseflow conditions. June 2008 measurements minimum and maximum values for inflow to Walker Creek were made to document the exchange of water between the (12199890), 12.4 and 13.8 ft3/s, respectively, and the error- groundwater system and creeks at a higher baseflow condition adjusted minimum and maximum values for flow at Walker with larger groundwater contributions. Streamflow during the Creek (12199890), 15.5 and 18.1 ft3/s, respectively, result in a August 2007 measurement period remained fairly constant at gain or loss uncertainty range (cumulative measurement error) the Carpenter Creek and Fisher Creek gaging stations and was of 1.7 to 5.7 ft3/s, and supports the delineation of a gaining steadily decreasing at the Nookachamps Creek gaging station reach indicated by the unadjusted value of 3.33 ft3/s. (fig. 20). Steadily decreasing streamflow in the study area was The synoptic streamflow data table( 5) illustrate a general observed during the June 2008 measurement period (fig. 21). pattern in which the upper reaches of creeks in the study area The results of the synoptic streamflow measurements tended to gain flow from the groundwater system, and lower are presented in table 5. Most measurements were rated creek reaches tended to lose flow fig.( 22). Substantial inflows “fair,” however, 17 measurements were rated “poor” from tributaries to major creeks in the study area suggest due to suboptimal flow conditions (low velocity, shallow the presence of groundwater discharge from upland areas depth, and aquatic vegetation), or the necessity to estimate underlain by bedrock. Pitz and Garrigues (2000) noted that streamflow values (lack of access to stream). Inflowtable ( 5) discharge to tributaries of Carpenter Creek are likely derived to a measurement site is the sum of streamflows measured in large part from groundwater fracture flow within upland upstream of the measurement site (fig. 22). For example: the bedrock areas during low-flow conditions. Groundwater August 2007 inflow to the Walker Creek measurement site discharge from permeable clastic units (OEc) also is a likely (12199890), 1.04 ft3/s, is the sum of the streamflows measured contributor to baseflow in upland areas. at the upstream Walker Creek site (12199860), 0.98 ft3/s, and the Tributary to Walker Creek site (12199870), 0.06 ft3/s. Inflow is used to compute the difference between streamflow Groundwater-Level Fluctuations upstream of the site and at the site. The sign of the difference Groundwater levels fluctuate over time, both seasonally in streamflow (positive or negative value) indicates a gaining and long term, in response to changing rates of recharge to or losing creek reach. and discharge from the groundwater system. When recharge Uncertainties associated with potential measurement exceeds discharge, the amount of water stored in an aquifer error were too large at a few locations to make defensible increases and water levels rise; when discharge exceeds conclusions regarding the delineation of gaining or losing recharge, groundwater storage decreases and water levels creek reaches and those values are identified in italic font decline. Groundwater levels also may respond to changes (table 5). Error-adjusted minimum and maximum values in nearby stream stage. When stream stage exceeds nearby of measured streamflows were used to evaluate potential groundwater levels, streamflow may recharge the aquifer, measurement error. Minimum and maximum values were causing a rise in groundwater levels; when groundwater levels computed by applying the measurement rating to the exceed nearby stream stage, discharge from the aquifer to streamflow value; a “fair” measurement rating applies an error the stream may occur, resulting in a decline in groundwater adjustment of ± 8 percent, and a “poor” rating applies an error levels. Seasonal changes in groundwater levels that follow a adjustment of ±10 percent. For example: the August 2007 typical pattern for shallow wells in western Washington were error-adjusted minimum and maximum values for inflow to observed in many tributary subbasin wells (Fasser and Julich, Walker Creek (12199890), 0.95 and 1.13 ft3/s, respectively, 2009). Water levels rise from October through March, when and the error-adjusted minimum and maximum values for flow precipitation and river stage are high, and decline from April at Walker Creek (12199890), 0.99 and 1.17 ft3/s, respectively, through September, when precipitation and river stage are result in a gain or loss uncertainty range (cumulative lower (figs. 23 and 24). measurement error) of -0.14–0.22 ft3/s. The uncertainty range Groundwater Movement 35

Table 5. Synoptic streamflow measurements and estimates of gains and losses in tributary subbasins, lower Skagit River basin, Washington, August 2007 and June 2008.

[Measurement site: Site locations are shown in figure 22. Inflow is the sum of streamflows measured upstream of the measurement site.Accuracy rating of the U.S. Geological Survey measurements: F, fair; P, poor; estimated values also are rated poor. Gain or Loss: Uncertainties associated with potential measurement error were too large at a few locations to make defensible conclusions regarding the delineation of gaining or losing creek reaches and those values are identified in italic. ft3/s, cubic feet per second]

Date discharge Discharge Accuracy Inflow Gain or loss Measurement site Site No. measured (ft3/s) rating (ft3/s) (ft3/s) East Fork Nookachamps Creek subbasin Walker Creek 12199860 08-08-07 0.98 F 06-17-08 12.8 F Tributary to Walker Creek 12199870 08-08-07 .06 P 06-17-08 .67 P Walker Creek 12199890 08-08-07 1.08 F 1.04 0.04 06-18-08 16.8 F 13.47 3.33 East Fork Nookachamps Creek 12199900 08-07-07 4.29 F 06-19-08 51.4 F East Fork Nookachamps Creek 03G100 08-07-07 15.10 4.29 .81 06-19-08 163.8 51.4 12.4 Mundt Creek 12200005 08-06-07 1.09 F 06-18-08 11.1 P East Fork Nookachamps Creek 12200010 08-07-07 4.58 F 6.19 -1.61 06-19-08 66.1 F 74.9 -8.8 Turner Creek 12200015 08-07-07 .50 F 06-18-08 2.48 F Inflow to Beaver Lake 12200022 08-07-07 .19 F 06-19-08 3.11 F Nookachamps Creek subbasin Lake Creek 12199300 08-06-07 0.47 F 06-17-08 9.35 F Lake Creek 12199400 08-07-07 1.13 F .47 .66 06-17-08 19.2 F 9.35 9.85 Nookachamps Creek 1219949950 08-09-07 .60 F 23.75 F 1.13 2.62 06-19-08 32.2 F 235.0 F 19.2 15.8 West Tributary to Nookachamps Creek 12199540 08-07-07 0.46 P 06-18-08 1.88 P East Tributary to Nookachamps Creek 12199560 08-09-07 .07 P 06-18-08 .39 P Nookachamps Creek 12199600 08-09-07 .76 F 1.13 -.37 06-19-08 33.1 F 34.47 -1.37 Carpenter Creek subbasin Carpenter Creek 12200682 08-09-07 0.08 P 06-16-08 3.71 F Carpenter Creek 12200684 08-09-07 .22 P 0.08 0.14 06-16-08 5.29 F 3.71 1.58 Carpenter Creek 12200685 08-09-07 .41 F .22 .19 06-16-08 8.89 F 5.29 3.60 Sandy Creek 12200686 07-23-07 .14 P 06-16-08 2.24 F Johnson Creek 12200688 08-09-07 .01 F 06-16-08 1.68 F 36 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Table 5. Synoptic streamflow measurements and estimates of gains and losses in tributary subbasins, lower Skagit River basin, Washington, August 2007 and June 2008.—Continued

[Measurement site: Site locations are shown in figure 23. Inflow is the sum of streamflows measured upstream of the measurement site.Accuracy rating of the U.S. Geological Survey measurements: F, fair; P, poor; estimated values also are rated poor. Gain or Loss: Uncertainties associated with potential measurement error were too large at a few locations to make defensible conclusions regarding the delineation of gaining or losing creek reaches and those values are identified in italic. ft3/s, cubic feet per second]

Date discharge Discharge Accuracy Inflow Gain or loss Measurement site Site No. measured (ft3/s) rating (ft3/s) (ft3/s) Carpenter Creek subbasin—Continued Bulson Creek 12200692 08-08-07 0.41 F 06-17-08 5.13 F Tributary to Bulson Creek 12200694 08-08-07 .49 P 06-17-08 2.21 F Carpenter Creek 12200696 09-21-00 3 2.22 1.46 0.76 06-19-08 12.4 F 20.15 -7.75 Fisher Creek subbasin Fisher Creek 12200698 08-08-07 4 0.01 P 06-18-08 41.50 P Fisher Creek 12200699 08-07-07 .00 4 0.01 -0.01 06-18-08 5.80 F 41.50 4.30 Fisher Creek 12200701 08-09-07 .49 P .00 .49 06-05-08 6.38 F 5.80 .58 Tributary to Fisher Creek 1220070120 08-07-07 .00 06-18-08 41.00 P Tributary to Fisher Creek 1220070140 08-07-07 4 .01 P 06-18-08 4 2.00 P 1 Daily mean streamflow at Ecology streamflow-gaging station; accuracy ratingassumed to be fair. 2 Includes measured streamflow plus evaporative loss from Big Lake table( 4). 3 Streamflow measured on September 20, 2000, accuracy rating assumed to be fair (Pitz and Garrigues, 2000); backwater conditions observed by the U.S. Geological Survey on August 8, 2007. 4 Estimated by U.S. Geological Survey.

140

Mean monthly streamflow (2001–08) 120 East Fork Nookachamps Creek Gaging Station No. 03G100 100

80

60

40 IN CUBIC SECOND FEET PER CUBIC IN MEAN MONTHLY MEANSTREAMFLOW, MONTHLY 20

0 OCT NOV DEC JAN FEB MAR APR MAY JUNE JULY AUG SEPT

Figure 19. Mean monthly streamflow (2001–08) for East Fork Nookachamps Creek at Washington State Department of Ecology streamflow-gaging station 03G100, lower Skagit River basin, Washington.

wa19_0386_Fig19 Groundwater Movement 37

2.0

1.8 August 2007 1.6 synoptic streamflow measurement period 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 DISCHARGE, IN CUBIC FEET PER SECOND FEET DISCHARGE,PER CUBIC IN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 AUGUST 2007 EXPLANATION Nookachamps Creek (12199600) Carpenter Creek (12200684) Fisher Creek (12200701)

Figure 20. Daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps (12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, August 1–15, 2007.

100 90 June 2008 80 synoptic streamflow 70 measurement period 60 50 40 30 20 10 0 DISCHARGE, IN CUBIC FEET PER SECOND FEET DISCHARGE,PER CUBIC IN 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 JUNE 2008 EXPLANATION Nookachamps Creek (12199600) Carpenter Creek (12200684) Fisher Creek (12200701)

Figure 21. Daily streamflow for U.S. Geological Survey streamflow-gaging stations on Nookachamps wa19_0386_Fig20(12199600), Carpenter (12200684), and Fisher (12200701) Creeks, lower Skagit River basin, Washington, June 10–25, 2008.

wa19_0386_Fig21 38 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

122°20' 122°10' T. 35 Skagit r Rive N.

N

oo

k ac Clear 12200022 ha mp Lake 0.19 C 3.11 r e e

Barney k Beaver Cr git Ri Lake r eek ka ver Lake e S Ea 12200015 n st ur 0.50 T

2.48 undt M C F r ee o k r 12200010

k 4.58 12200005 N 66.1 T. o 1.09 o k 11.1 34 12199600 a c N. 0.76 h 03G100 33.1 a N 5.10 m o 63.8 p o 48°25' s k a 12199560 c 12199900

h k 4.29 e 0.07 a e m r 0.39 p 51.4 C 12199540 C s r 0.46 e 12199890 e

1.88 k 1.08 16.8 W C 1219949950 a a l r 0.60 3.75 k p e e 32.2 35.0 r 12199870 For k n

h 0.06 t t e r

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r e T. e k 32 N. R.3 E. R.4 E. R.5 E. R.6 E. Base from U.S. Geological Survey and/or Washington Division of Geology and Earth Resources 0 1 2 3 4 5 MILES digital data, 1983, 1:100,000 Universal Transverse Mercator projection, Zone 10 Horizontal Datum: North American Datum of 1927 (NAD 27) 43210 5 KILOMETERS Streamflow-gaging stations EXPLANATION 03G100 Ecology Boundary of tributary subbasin 12200701 U.S. Geological Survey 12200005 Synoptic streamflow site—Discharge 1.09 11.1 in cubic feet per second August 2007 June 2008

Figure 22. Locations of stream sites where streamflow was measured to determine groundwater discharge and delineate gaining and losing stream reaches in tributary subbasins and vicinity, lower Skagit River basin, Washington, August 2007 and June 2008.

tac09-9722-0328 Upper Skagit Geo_Fig 22 Groundwater Movement 39

9 0 4.5 Well No 34N/05E-32P01 8 1 Nookachamps Creek Gaging Station No 12199600 4.0 Monthly precipitation at Sedro-Woolley 7 2 3.5

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Figure 23. Water levels in well 34N/05E-32P01, stream stage at U.S. Geological Survey steamflow- gaging station on Nookachamps Creek (12199600), and precipitation at Sedro-Woolley, lower Skagit River basin, Washington, April 2007–August 2008.

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Figure 24. Water levels in well 33N/04E-28M01, stream stage at U.S. Geological Survey streamflow- gaging station on Fisher Creek (12200701), and precipitation at Sedro-Woolley, lower Skagit River basin, Washington, April 2007–August 2008.

tac09-9722-0386_Fig 23

tac09-9722-0386_Fig 24 40 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

The timing and magnitude of seasonal groundwater- Water Budget level fluctuations in an aquifer system are related to the hydraulic characteristics of aquifer materials and adjacent On a long-term basis, a hydrologic system is usually in confining units, the presence of unconfined or confined aquifer a state of dynamic equilibrium; that is, inflow to the system conditions, the depth to groundwater, and the depth of the equals outflow from the system, and there is little or no change well and screened intervals being measured. Water levels in in the amount of water stored within the system. An estimated deep wells typically respond to changes in recharge more water budget for average precipitation during the study slowly and with less magnitude than water levels in shallow period (September 1, 2006, to August 31, 2008) in the four wells, because deep wells are usually farther from the source tributary subbasin area, as well as each individual subbasin, of recharge, and variability is dampened. The largest water- is presented in table 7. The methods used to estimate values level fluctuations observed during the monitoring period of precipitation, groundwater recharge, and groundwater (October 2006 through September 2008) occurred in wells discharge to creeks are described in previous sections of this completed in the sedimentary aquifer (OEc), and ranged from report. Surface runoff, including shallow subsurface flow, was about 3 to 27 ft (table 6). These unexpectedly large water- computed as a residual; that is, it represents the quantity that level fluctuations in relatively deep sedimentary aquifer wells remains after groundwater discharge to creeks is subtracted may be attributed to several factors including the presence of from total streamflow. The value for evapotranspiration also is water-bearing fractures (high conductivity and low storage) a residual and was computed as the quantity that remains after within local outcrop areas receiving precipitation recharge, surface runoff plus groundwater recharge is subtracted from and the relatively lower storage capacity of cemented precipitation. Precipitation during the study period (September sediments compared to sands and gravels (Freeze and Cherry, 1, 2006, to August 31, 2008) averaged an estimated 56 1979; Fetter, 1988). Water levels in wells completed in in/ yr over the tributary subbasins. Approximately one-third the unconsolidated hydrogeologic units exhibited seasonal (33 percent) of precipitation enters the groundwater system in variations ranging from less than 1 to about 10 ft. the subbasins as groundwater recharge. Most of this recharge (65 percent) discharges to creeks, and only about 3 percent is withdrawn from wells. The remaining groundwater recharge (32 percent) leaves the subbasin groundwater system as discharge to the Skagit River and Puget Sound.

Table 6. Statistical summary of groundwater-level fluctuations and well depth by hydrogeologic unit in tributary subbasins and vicinity, lower Skagit River basin, Washington, October 2006 through September 2008.

[–, no data]

Water-level fluctuation Well depth Number Hydrogeologic unit (feet) (feet below land surface) of wells Minimum Median Maximum Minimum Median Maximum Qago Alluvial and recessional outwash aquifer 7 2.72 5.96 7.37 17 35 58 Qgt Till confining unit 5 1.65 5.82 6.78 10 20 35 Qga Advance outwash aquifer 13 0.52 4.09 10.23 40 80 152 Qgl Glaciolacustrine and distal outwash confining unit 2 1.25 4.34 7.42 25 103 180 Qco Inter-glacial alluvial aquifer 4 0.96 1.69 2.57 126 268 366 Qot Older till confining unit 0 – – – – – – Qooa Older outwash and alluvial aquifer 2 3.00 3.21 3.42 240 248 256 OEc Sedimentary aquifer 12 3.28 10.51 27.49 15 241 500 EJTP Igneous and metamorphic bedrock unit 2 1.50 5.75 10.00 124 252 380 Groundwater Movement 41

Table 7. Estimated average annual water budget for tributary subbasins, lower Skagit River basin, Washington, September 1, 2006, to August 31, 2008.

[<. less than]

Quantity Quantity Water-budget component Inches Acre-feet Percent Water-budget component Inches Acre-feet Percent per year per year per year per year All subbasins Precipitation Precipitation Fate of precipitation Fate of precipitation Surface runoff 18 17,720 38 Surface runoff 20 100,200 35 Evapotranspiration 11 11,690 25 Evapotranspiration 18 91,400 32 Groundwater recharge 17 17,200 37 Groundwater recharge 18 92,400 33 Total precipitation 46 46,610 100 Total precipitation 56 284,000 100 Fate of recharge Discharge to creeks 5 5,480 32 Fate of recharge Other natural discharge 10 9,880 57 Discharge to creeks 12 60,400 65 Withdrawals from wells 2 1,840 11 Other natural discharge 6 29,800 32 Withdrawals from wells <1 2,200 3 Total recharge 17 17,200 100 Total recharge 18 92,400 100 Fisher Creek subbasin East Fork Nookachamps Creek subbasin Precipitation Precipitation Fate of precipitation Fate of precipitation Surface runoff 8 4,610 18 Surface runoff 27 52,960 39 Evapotranspiration 20 10,820 42 Evapotranspiration 22 42,900 31 Groundwater recharge 19 10,300 40 Groundwater recharge 21 41,060 30 Total precipitation 47 25,730 100 Total precipitation 70 136,920 100 Fate of recharge Fate of recharge Discharge to creeks 7 3,590 35 Discharge to creeks 18 34,740 85 Other natural discharge 12 6,580 64 Other natural discharge 3 6,300 15 Withdrawals from wells <1 130 1 Withdrawals from wells <1 20 <1 Total recharge 19 10,300 100 Total recharge 21 41,060 100 Nookachamps Creek subbasin Precipitation Fate of precipitation Surface runoff 16 24,870 33 Evapotranspiration 17 26,110 35 Groundwater recharge 16 23,840 32 Total precipitation 49 74,820 100

Fate of recharge Discharge to creeks 11 16,610 70 Other natural discharge 5 7,020 30 Withdrawals from wells <1 210 <1 Total recharge 16 23,840 100 Carpenter Creek subbasin 42 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Summary and Conclusions Unconsolidated aquifers (Qago, Qga, Qco, and Qooa) typically consist of moderately to well-sorted alluvial and Recent population growth along the Interstate 5 corridor glacial outwash deposits of sand, gravel, and cobbles, with near Mount Vernon, Washington, has led to increased water minor lenses of silt and clay. These units typically occur as use, with many new domestic wells serving residents in the discontinuous or isolated bodies, and are of highly variable lower Skagit River basin in areas not served by a regional thickness. Unconfined conditions exist in areas where aquifer public-water system. Planning for future development units are present at land surface; however, much of the in the lower basin, including the reservation of water for study area is mantled by glacial till, and confined aquifer new domestic wells, requires identification of areas where conditions are common. Estimated hydraulic conductivity withdrawals from existing and new wells could adversely for the aquifers ranged from 0.27 ft/d (OEc) to 57 ft/d (Qco). impact streamflow in the Skagit River or its tributaries. A Groundwater in the unconsolidated aquifers generally flows study to characterize the groundwater/surface-water flow towards the northwest and west in the direction of the Skagit system in four tributary subbasins of the lower Skagit River River and Puget Sound. This generalized flow pattern is likely was conducted by the U.S. Geological Survey to assist Skagit complicated by the presence of low permeability confining County and the Washington State Department of Ecology in units that separate discontinuous bodies of aquifer material evaluating the effects of potential groundwater withdrawals and act as local groundwater flow barriers. Water-level altitude and consumptive use on tributary streamflows. differences between the advance outwash (Qga) and inter- The study area covers about 247 square miles along the glacial alluvial (Qco) aquifers in the southwestern part of the Skagit River and its tributary subbasins in southwestern Skagit study area suggest downward vertical flow. The potential for County and northwestern Snohomish County, Washington. upward groundwater movement, indicated by the presence of The Skagit River occupies a large, relatively flat alluvial flowing wells, was observed at several locations within the valley that is bounded to the south and east by upland and aquifer units. mountainous terrain. The alluvial valley primarily is underlain Unconsolidated confining units (Qgt, Qgl, and Qot) by fluvial sand and gravel deposits, and locally preserved lahar typically consist of poorly sorted glacial till, glaciolacustrine, runout deposits. Upland areas contain laterally discontinuous and landslide deposits of clay, silt, sand, gravel, cobbles, bodies of glacial (till and outwash) and interglacial (fluvial and boulders, with locally occurring sand and gravel lenses and lacustrine) deposits of varying thickness that reflect both capable of providing water for domestic use. Estimated terrestrial and shallow marine depositional environments. hydraulic conductivity for the confining units ranged from Bedrock consisting of metamorphic rocks, sedimentary units, 0.13 ft/d (EJTP) to 26 ft/d (Qgl). The Vashon Till (Qgt) is and igneous rocks underlies the alluvial valley and upland present throughout much of the study area; other confining areas, and crops out throughout the mountainous terrain. The units are more limited in extent. southwest flowing Skagit River receives streamflow from The sedimentary aquifer (OEc) is present in large parts four tributary subbasins (East Fork Nookachamps Creek, of the glacial upland and mountains in central and southern Nookachamps Creek, Carpenter Creek, and Fisher Creek) that parts of the study area and consists primarily of conglomerate originate within the mountainous interior of the study area. and sandstone with fine-grained intervals. Confined conditions The lower reaches of most creeks flow year-round, however, are likely where the aquifer is fully saturated and overlain intermittent flow conditions are common in middle and upper by glacial confining units; fine-grained intervals within creek reaches during the summer months. the aquifer also may produce locally confined conditions. A simplified surficial geologic map was compiled Groundwater flow directions in the sedimentary aquifer likely from previous mapping in the area, and geologic units were reflect local topographic relief (radial flow from bedrock differentiated into nine hydrogeologic units: Alluvial and highs) and more regional westward flow from the mountains recessional outwash aquifer (Qago), Till confining unit (Qgt), to the Puget Sound. Advance outwash aquifer (Qga), Glaciolacustrine and distal The igneous and metamorphic bedrock unit (EJTP) is outwash confining unit (Qgl), Inter-glacial alluvial aquifer present along the northern margin of the glacial uplands in (Qco), Older till confining unit (Qot), Older outwash and the mountains along the eastern margin of the study area, alluvial aquifer (Qooa), Sedimentary aquifer (OEc), and and within segments of the Darington-Devils Mountain Fault Igneous and metamorphic bedrock unit (EJTP). A surficial Zone. This low-permeability unit is composed of volcanic hydrogeologic unit map was constructed and used with and metamorphic rocks and consists of rhyolite, andesite, drillers’ logs from 296 wells to produce four hydrogeologic basalt, and complex assemblages of low-grade metasediments, sections, and unit extent and thickness maps. metavolcanics, and meta-intrusives, and is considered to be non-water bearing except in localized areas of fracturing. Selected References 43

The largest groundwater level fluctuations observed Booth, D.B., 1994, Glaciofluvial infilling and scour of the during the monitoring period (October 2006 through Puget Lowland, Washington, during ice-sheet glaciation: September 2008) occurred in wells completed in the Geology, v. 22, no. 8, p. 695-698. sedimentary aquifer, and ranged from about 3 to 27 feet. Water levels in wells completed in unconsolidated hydrogeologic Carnahan, B., Luther, H.A., and Wilkes, J.O., 1969, Applied units exhibited seasonal variations ranging from less than 1 to numerical methods: New York, John Wiley and Sons, Inc., about 10 feet. Synoptic streamflow measurements made in 604 p. August 2007 and June 2008 indicate groundwater discharge Daly, Christopher, Neilson, R.P., and Phillips, D.L., 1994, A to creeks in the subbasins ranged from about 13.15 to statistical-topographic model for mapping climatological 129.6 cubic feet per second (9,520 to 93,830 acre-feet per precipitation over mountainous terrain: Journal of Applied year), respectively. Streamflow measurements illustrate a Meteorology, v. 33, no. 2, p. 140–158. general pattern in which the upper reaches of creeks in the study area tended to gain flow from the groundwater system, Dethier, D.P., Whetten, J.T., and Carroll, P.R., 1980, and lower creek reaches tended to lose water. Significant Preliminary geologic map of the Clear Lake SE quadrangle, inflows from tributaries to major creeks in the study area Skagit County, Washington: U.S. Geological Survey Open- suggest the presence of groundwater discharge from upland File Report 80-303, 11 p., 2 plates. areas underlain by bedrock. The groundwater system within the subbasins received Dethier, D.P., and Whetten, J.T., 1980, Preliminary geologic an average (September 1, 2006, to August 31, 2008) of map of the Clear Lake SW quadrangle, Skagit and about 92,400 acre-feet or about 18 inches of recharge from Snohomish Counties, Washington: U.S. Geological Survey precipitation a year. Most of this recharge (65 percent) Open-File Report 80-825, 11 p., 2 plates. discharges to creeks, and only about 3 percent is withdrawn Dethier, D.P., and Whetten, J.T., 1981, Preliminary geologic from wells. The remaining groundwater recharge (32 percent) map of the Mount Vernon 7.5-minute quadrangle, Skagit leaves the subbasin groundwater system as discharge to the County, Washington: U.S. Geological Survey Open-File Skagit River and Puget Sound. Report 81-105, 10 p., 1 plate, scale 1:24,000. Dragovich, J.D., and DeOme, A.J., 2006, Geologic map of the McMurray 7.5-minute quadrangle, Skagit and Snohomish Acknowledgments Counties, Washington: Washington Division of Geology and Earth Resources Geologic Map GM-61, 18 p., 1 sheet, The authors wish to thank the many well owners in the scale 1:24,000. study area who provided access to their wells during this study, and special thanks go to the property owners who Dragovich, J.D., Gilbertson, L.A., Norman, D.K., Anderson, allowed observation wells to be installed on their property. Joe Garth, and Petro, G.T., 2002, Geologic map of the Utsalady Dragovich and other staff of the Washington State Department and Conway 7.5-minute quadrangles, Skagit, Snohomish, of Natural Resources generously provided interpretive and Island Counties, Washington: Washington Division of data that was crucial to the subsurface identification and Geology and Earth Resources Open-File Report 2002-5, delineation of geologic units, and the development of the 34 p., 2 sheets, scale 1:24,000. hydrogeologic framework presented in this report. The authors gratefully acknowledge this significant contribution. The Dragovich, J.D., and Grisamer, C.L., 1998, Quaternary authors also wish to thank Skagit County and the Washington stratigraphy, cross sections, and general geohydrologic State Department of Ecology for providing assistance in the potential of the Bow and Alger 7.5-minute quadrangles, compilation of well information. western Skagit County, Washington: Washington Division of Geology and Earth Resources Open File Report 98-8, 30 p., 6 plates. Selected References Dragovich, J.D., Pringle, P.T., and Walsh, T.J., 1994, Extent and geometry of the Mid-Holocene Osceola Mudflow in the Puget Lowland—Implications for Holocene sedimentation Bear, Jacob, 1979, Hydraulics of groundwater: New York, and paleogeography: Washington State Department of McGraw-Hill, 569 p. Natural Resources, Washington Geology, v. 22, no. 3, Bidlake, W.R., and Payne, K.L., 2001, Estimating recharge to p. 3-26. ground water from precipitation at Naval Submarine Base Bangor and Vicinity, Kitsap County, Washington: U.S. Geological Survey Water- Resources Investigations Report 01-4110, 33 p. 44 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

Dragovich, J.D., Troost, M.L., Norman, D.K., Anderson, Marcus, K.L., 1981, The rocks of Bulson Creek–Eocene- Garth, Cass, Jason, Gilbertson, L.A., and McKay, D.T., Oligocene sedimentation and tectonics in the Lake Jr., 2000, Geologic map of the Anacortes South and McMurray area, Washington: Western Washington La Conner 7.5-minute quadrangles, Skagit and Island University M.S. thesis, 84 p., 1 plate. Counties, Washington: Washington Division of Geology and Earth Resources Open File Report 2000-6, 4 sheets, National Land Cover Database, 2001: accessed May, 2009, scale 1:24,000. http://www.mrlc.gov/multizone_download.php?zone=1. Drost, B.W., 2005, Quality-assurance plan for ground-water National Oceanic and Atmospheric Administration, 1982, activities, U.S. Geological Survey, Washington Water Evaporation atlas for the contiguous 48 United States: Science Center: U.S. Geological Survey Open-File Report NOAA Technical Report NWS 33, 27 p., 4 plates. 05-1126, 27 p. http://pubs.usgs.gov/of/2005/1126/. National Oceanic and Atmospheric Administration, 2007, Easterbrook, D.J., 1969, Pleistocene chronology of the Puget Climatological data, annual summary, Washington, 2007: Lowland and San Juan Islands, Washington: Geological Asheville, North Carolina, National Climatic Data Center, Society of America Bulletin, v. 80, no. 11, p. 2273-2286. v.111, no. 13, 30 p. Fasser, E.T., and Julich, R.J., 2009, Hydrographs showing Oregon State University, 2009, PRISM Products: accessed ground-water level changes for selected wells in the Lower May, 2009 at http://www.prism.oregonstate.edu. Skagit River basin, Washington: U.S. Geological Survey Pessl, Fred, Jr., Dethier, D.P., Booth, D.B., and Minard, J.P., Data Series 441. 1989, Surficial geologic map of the Port Townsend 30- by Ferris, J.G., Knowles, D.B., Brown, R.H., and Stallman, R.W., 60-minute quadrangle, Puget Sound region, Washington: 1962, Theory of aquifer tests: U.S. Geological Survey U.S. Geological Survey Miscellaneous Investigations Water-Supply Paper 1536-E, 174 p. Series Map I-1198-F, 1 sheet, scale 1:100,000, with 13 p. text. Fetter, C.W., 1988, Applied hydrogeology: Columbus, OH, Merrill Publishing Company, 592 p. Pitz, C.F., and Garrigues, R.S., 2000, Summary of streamflow conditions, September 2000, Fisher Creek and Carpenter Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Creek Basin: Washington State Department of Ecology Englewood Cliffs, NJ, Prentice-Hall, 604 p. Publication no. 00-03-049, 44 p. GeoEngineers, 1996, Geologic/hydrogeologic services, water Rantz, S.E., 1982, Measurement and computation of resources plan, Skagit County, Washington: File no. 2402- streamflow, volume 1—Measurement of stage and 006-73/121196, 389 p., 4 plates. discharge: U.S. Geological Survey Water-Supply Paper 2175, 284 p. GeoEngineers, 2003, Lower and upper Skagit watershed plan Samish River sub-basin, ground water hydrology Schuster, J.E., 2000, 1:100,000-scale digital geology of evaluation: File no. 7291-001-00-1180, 175 p. Washington State: Washington Division of Geology and Earth Resources: Digital Coverage. Hansen, H.P., and Mackin, J.H., 1949, A pre-Wisconsin forest succession in the Puget Lowland, Washington: American Skagit County Assessor, 2008, domestic connections: Journal of Science, v. 247, no. 12, p. 833-855. accessed March, 2008, at http://www.skagitcounty.net/ Common/Asp/Default.asp?d=GIS&c=General&p=Digital/ Hutchinson, M.F., 1989, A new method for gridding elevation main.htm. and streamlining data with automated removal of pits: Journal of Hydrology, v. 106, p. 211-232. Snohomish County Assessor, 2008, domestic connections: accessed April 2008, at http://www1.co.snohomish.wa.us/ Johnson, S.Y., 1982, Stratigraphy, sedimentology, and tectonic Departments/PDS/Divisions/LR_Planning/Information/ setting of the Eocene Chuckanut Formation, northwest Maps/mapsgisdata.htm. Washington: University of Washington Ph.D thesis, 221 p., 4 plates. Lane, R.C., 2009, Estimated water use in Washington, 2005: U.S. Geological Survey Scientific Investigations Report 2009–5128, 30 p. Selected References 45

Tabor, R.W., 1994, Late Mesozoic and possible Early Tertiary Washington State Department of Health, 2008, Public supply accretion in western Washington State–The Helena- connections: accessed March, 2008, at http://www4.doh. Haystack mélange and the Darrington-Devils Mountain wa.gov/sentryinternet/Intro.aspx fault zone: Geological Society of America Bulletin, v. 106, no. 2, p. 217-232, 1 plate. Western Regional Climate Center, 2008: accessed November, 2009, at http://www.wrcc.dri.edu/cgi-bin/cliMONtpre. Thomas, B.E., Wilkinson, J.M., and Embrey, S.S., 1997, The pl?wa7507 ground-water system and ground-water quality in western Snohomish County, Washington: U.S Geological Survey Whetten, J.T., Carroll, P.I., Gower, H.D., Brown, E.H., and Water-Resources Investigations Report 96-4312, 218 p., Pessl, Fred, Jr., 1988, Bedrock geologic map of the Port 9 plates. Townsend 30- by 60-minute quadrangle, Puget Sound region, Washington: U.S. Geological Survey Miscellaneous U.S. Census Bureau, 2000: accessed April, 2008, at http:// Investigations Series Map I-1198-G, 1 sheet, scale www.census.gov/census2000/states/wa.html. 1:100,000. U.S. Department of Agriculture Natural Resources Whetten, J.T., Dethier, D.P., and Carroll, P.R., 1979, Conservation Service, 2007, crop irrigation rates and Preliminary geologic map of the Clear Lake NE quadrangle, methods: accessed March, 2009, at http://www.wa.nrcs. Skagit County, Washington: U.S. Geological Survey Open- usda.gov/technical/ENG/irrigation_guide/index.html. File Report 79-1468, 10 p., 2 plates. Washington State Department of Agriculture, 2008, crop Whetten, J.T., Dethier, D.P., and Carroll, P.R., 1980, location maps: accessed January, 2009 at http://agr.wa.gov/ Preliminary geologic map of the Clear Lake NW PESTFERT/NatResources/AgLandUse.aspx. quadrangle, Skagit County, Washington: U.S. Geological Survey Open-File Re port 80-247, 12 p., 2 plates. Washington State Department of Ecology, 2009, river and stream flow monitoring: accessed February, 2009, at http:// www.ecy.wa.gov/programs/eap/flow/shu_main.html. 46 Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington

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For more information concerning the research in this report, contact the Director, Washington Water Science Center U.S. Geological Survey, 934 Broadway — Suite 300 Tacoma, Washington 98402 http://wa.water.usgs.gov/ Savoca and others— Hydrogeologic Framework, Groundwater Movement, and Water Budget, Lower Skagit River Basin, Washington—Scientific Investigations Report 2009–5270