Hydrogeologic framework, groundwater movement, and water budget in the Puyallup River Watershed and vicinity, Pierce and King Counties, Washington

Scientific Investigations Report 2015-5068
Prepared in cooperation with the Cities of Auburn, Milton, Puyallup, Sumner, and Tacoma; Pierce Conservation District; Washington State Department of Health; Cascade Water Alliance; Lakehaven Utility District; Summit Water & Supply Company; Mt. View-Edgewood Water Company; and The Russell Family Foundation
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Abstract

This report presents information used to characterize the groundwater-flow system in the Puyallup River Watershed and vicinity, and includes descriptions of the geology and hydrogeologic framework; groundwater recharge and discharge; groundwater levels and flow directions; seasonal groundwater level fluctuations; interactions between aquifers and the surface-water system; and a water budget. The study area covers about 1,220 square miles in northern Pierce and southern King Counties, Washington; extends north to the Green River and Auburn Valley and southwest to the Puyallup River and adjacent uplands; and is bounded on the south and east by foothills of the Cascade Range and on the west by Puget Sound. The area is underlain by a northwest-thickening sequence of unconsolidated glacial and interglacial deposits, which overlie sedimentary and volcanic bedrock units that crop out in the foothills along the southern and eastern margin of the study area. Geologic units were grouped into 13 hydrogeologic units consisting of aquifers, confining units, and an underlying bedrock unit. A surficial hydrogeologic unit map was developed and used with well information from 1,012 drillers’ logs to construct 8 hydrogeologic sections, and unit extent and thickness maps.

Groundwater in unconsolidated glacial and interglacial aquifers generally flows to the northwest towards Puget Sound, and to the north and northeast towards the Puyallup River, White River, and Green River valleys. These generalized flow patterns are complicated by the presence of low permeability confining units and bedrock that separate discontinuous bodies of aquifer material and act as local groundwater-flow barriers. Water levels in wells completed in the unconsolidated hydrogeologic units show seasonal variations ranging from less than 1 to about 32 feet during the monitoring period (March 2011–March 2013).

Synoptic streamflow measurements made in October 2011 and October 2012 indicated a total groundwater discharge to streams in the water-budget area (520 square miles located within the larger study area) of at least 349,000 and 280,000 acre-feet per year, respectively. Annual groundwater discharge to streams likely exceeds these values because streamflow measurements were made during the dry, late-summer and early-autumn period when groundwater levels typically are at annual lows. Most stream reaches in the study area either gain flow from groundwater discharge or exhibit near-neutral conditions with no substantial gain or loss of flow. Groundwater discharge occurs at numerous springs in the area; the total reported discharge of springs in the area is approximately 80,300 acre-feet per year.

The water-budget area received about 1,428,000 acre-feet or about 52 inches of precipitation per year (January 1, 2011, to December 31, 2012). About 41 percent of precipitation enters the groundwater system as recharge. Seven percent of this recharge is withdrawn from wells and the remainder leaves the groundwater system as discharge to rivers, discharge to springs, or submarine discharge to Puget Sound, or exits the study area through subsurface flow in the Green River valley.

Study Area

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Hydrogeologic framework, groundwater movement, and water budget in the Puyallup River Watershed and vicinity, Pierce and King Counties, Washington
Series title Scientific Investigations Report
Series number 2015-5068
DOI 10.3133/sir20155068
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Washington Water Science Center
Description Report: vii, 53 p.; 4 Plates: 51.75 x 32.5 inches or smaller; Appendix A
Country United States
State Washington
County King County, Pierce County
Other Geospatial Puyallup River Watershed
Datum North American Datum of 1983
Projection State Plane Washington South
Online Only (Y/N) Y
Additional Online Files (Y/N) Y