A DESCRIPTION OF HYDROGEOLOGIC UNITS IN THE PORTLAND BASIN, OREGON AND WASHINGTON U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 90-4196 Prepared in cooperation with CITY OF PORTLAND BUREAU OF WATER WORKS, INTERGOVERNMENTAL RESOURCE CENTER and OREGON WATER RESOURCES DEPARTMENT A DESCRIPTION OF HYDROGEOLOGIC UNITS IN THE PORTLAND BASIN, OREGON AND WASHINGTON By R.D. Swanson, W.D. McFarland, J.B. Gonthier, and J.M. Wilkinson U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 90-4196 Prepared in cooperation with CITY OF PORTLAND BUREAU OF WATER WORKS, INTERGOVERNMENTAL RESOURCE CENTER, and OREGON WATER RESOURCES DEPARTMENT Portland, Oregon 1993 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director For additional information Copies of this report can write to: be purchased from: Oregon Office Chief U.S. Geological Survey U.S. Geological Survey Books and Open-File Reports Section 10615 S.E. Cherry Blossom Drive Federal Center, Box 25425 Portland, OR 97216 Denver, CO 80225 11 CONTENTS Page Abstract --------------------------------------------------------- 1 Introduction ----------------------------------------------------- 1 Purpose and scope ------------------------------------------- 5 Acknowledgments --------------------------------------------- 5 Previous investigations ------------------------------------- 5 Methods of investigation ------------------------------------ 7 Geologic setting ------------------------------------------------- 9 Older rocks ------------------------------------------------- 9 Sandy River Mudstone and Troutdale Formation ---------------- 10 Cascade Range volcanics and Boring Lava --------------------- 13 Late Pliocene to Holocene sediments ------------------------- 14 Geologic structure ----------------------------------------------- 15 Hydrogeologic units ---------------------------------------------- 17 Older rocks subsystem --------------------------------------- 19 Lower sedimentary subsystem --------------------------------- 21 Sand and gravel aquifer -------------------------------- 21 Confining unit 2 --------------------------------------- 23 Troutdale sandstone aquifer ---------------------------- 24 Confining unit 1 --------------------------------------- 25 Undifferentiated fine-grained sediments ---------------- 26 Upper sedimentary subsystem --------------------------------- 26 Troutdale gravel aquifer ------------------------------- 27 Unconsolidated sedimentary aquifer --------------------- 29 Summary ------------- --------------------------------------------- 30 Selected references ---------------------------------------------- 32 iii ILLUSTRATIONS Plate 1. Hydrogeologic units in the Portland Basin. 2. Hydrogeologic sections in the Portland Basin. 3. Altitude of top of older rocks. 4. Altitude of top and thickness of sand and gravel aquifer, 5. Altitude of top and thickness of confining unit 2. 6. Altitude of top and thickness of the Troutdale sandstone aquifer. 7. Altitude of top and thickness of the confining unit 1. 8. Altitude of top and thickness of the undifferentiated fine-grained sediments. 9. Altitude of top and thickness of the Troutdale gravel aquifer. 10. Thickness of the unconsolidated sedimentary aquifer. Figure 1. Map showing location of the Portland Basin study area ------------------------------------------------ 2 2. Map showing regional geology of the Portland Basin ---- 3 3. Summary of geologic and hydrogeologic units ----------- 12 4. Comparison of hydrogeologic unit terminology for the Portland Basin ---------------------------------- 18 TABLES Table 1. Altitude of the top of hydrogeologic units for selected wells, in feet ---------------------------- 37 IV CONVERSION FACTORS AND ABBREVIATIONS Multiply By To obtain Length foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area acre 4,047. square meters (m2 square mile (mi 2 ) 2.590 square kilometer (km2 ) Volume gallon (gal) 3.785 liter (L) Flow gallon per minute (gal/min) 0.0631 liter per second (L/s) Sea level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)--a geodetic datum derived from a general adjustment of the first order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929. v Well-location System The system used in this report for locating wells is based on the rectangular system for subdivision of public land. The numbers and characters represent successively the township, range, section, and location within the section by quarter section (160 acres), quarter- quarter section (40 acres), quarter-quarter-quarter section (10 acres), and quarter-quarter-quarter-quarter section (2.5 acres). Where necessary, serial numbers are added after the final letter to assure uniqueness of location numbers. An alternative location system, used previously in the State of Oregon and currently in use in the State of Washington, is also illustrated. This system uses a single capital letter to represent the quarter-quarter section (40 acres) in which a well is located. R.1W. R.2E. R.4E. R.6E. T.3N. T.1N. T.1S. ALTERNATIVE LOCATION D C B A SYSTEM 1N/2E-29J E F G H 2 9 M L K *j i N P Q R vi A DESCRIPTION OF HYDROGEOLOGIC UNITS IN THE PORTLAND BASIN, OREGON AND WASHINGTON By R.D. Swanson, W.D. McFarland, J.B. Gonthier, and J.M. Wilkinson ABSTRACT The increasing reliance on ground-water resources in the Portland Basin has prompted a need to evaluate the capability of the ground-water system to meet present and future demands. Toward this goal, the U.S. Geological Survey conducted a hydrogeologic study of the basin and is constructing a ground-water flow model of the aquifer system. This report describes one component of the study which involved mapping the extent, thickness, and boundaries of hydrogeologic units (aquifers and confining units) in the basin. Hydrogeologic units in the basin were mapped using data from field- located water, cathodic protection, geothermal, and oil and gas wells, borehole geophysical logs, borehole sampling, and detailed surficial hydrogeologic mapping. These data were entered into a geographic information system for analysis and to produce digital maps for input into the ground-water model. Eight major hydrogeologic units were mapped in the Portland Basin. From oldest to youngest these units include: older rocks, sand and gravel aquifer, confining unit 2, Troutdale sandstone aquifer, confining unit 1, consolidated gravel aquifer, and an unconsolidated sedimentary rock aquifer. The eighth unit is an undifferentiated fine-grained unit that is lithologically similar to the confining units. It exists where the sand and gravel aquifer and the Troutdale sandstone aquifer pinch out in the western and northwestern parts of the basin or sufficient information does not exist to map the sand and gravel aquifer. INTRODUCTION The Portland Basin is located in northwestern Oregon and southwestern Washington (fig. 1) and includes about 1,300 square miles. The term "Portland Basin" is used to describe the northwest-southeast trending, sediment-filled structural depression bounded by the Tualatin Mountains (locally referred to as the Portland Hills) on the west and the Cascade Range (includes Western Cascades and High Cascades) on the east, north, and south (fig. 2). The City of Portland and many of its suburbs are centrally located in the Portland Basin and represent the largest urban area in Oregon. Both surface- and ground-water resources are important to the Portland- Vancouver metropolitan region. 122M5' 46'00' - L_r: WASHlkGTON]_. 30' - ilwaukie\ CLACKAMAS .Boring Damascus Modified from Metropolitan Service District, Major Arterial map, 1984 10 KILOMETERS Figure 1. Location of the Portland Basin study area. 123 122 Boring Lava and High ' °°°Z°'fi Cascade volcanics ; ! 2-il Late Tertiary and . tx ,x^ii Quaternary consolidated* sedimentary rocks . ». i. , e . ,..,.> ..> + + t + 4 + + + + _ . + + + + + t t t + + + t %t . t 0 5 10 KILOMETERS Figure 2. Regional geography of the Portland Basin. Modified from: Wells and Peck (1961), Sherrod and Smith (1989), and Walsh and others (1987). Portland and neighboring Oregon communities obtain most of their drinking-water supplies from the Bull Run Watershed which is approximately 20 miles southeast of Portland on the western flank of the Cascade Range. During peak-use periods in the summertime, the Bull Run surface-water system can supply more than 200 million gallons of water each day. The City of Portland has constructed a well field in the Portland Basin, capable of producing more than 100 million gallons of water each day, to provide a backup or emergency supply of water to the Portland area in the event that the Bull Run system was unable to supply the needed water. Most other water users in the Oregon part of the Portland Basin obtain water for domestic and irrigation uses from ground-water resources. These rural areas include parts of Columbia, Multnomah, and Clackamas Counties. The Washington part of the basin, which includes all of Clark County, relies almost entirely on ground water for public supply, domestic, industrial, and irrigation water. The primary suppliers of public drinking water in the Clark County area are the City of Vancouver and the Public Utility District of Clark County. Most water in rural Clark County is supplied by individual private well systems. Because of the increasing dependence on ground-water resources in the Portland Basin, agencies charged with managing the resource