Conversion Factors

Multiply	By	To obtain
acre	0.4047	hectare (ha)
foot (ft)	0.3048	meter (m)
mile (mi)	1.609	kilometer (km)
section (640 acres or 1 mi2)	259.0	square hectometer (hm2)
square mile (mi2)	2.590	square kilometer (km2)

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88).

Abstract

Groundwater levels for selected wells in the Chehalis River basin, Washington, are presented on an interactive web-based map to document the spatial distribution of groundwater levels in the study area during late summer 2009. Groundwater level data and well information were collected by the U.S. Geological Survey using standard techniques. The data are stored in the USGS National Water Information System (NWIS), Ground-Water Site-Inventory (GWSI) System.

Introduction

This report describes part of a larger cooperative study by the U.S. Geological Survey (USGS), the Washington State Department of Ecology, U.S. Army Corps of Engineers, and the Chehalis Basin Partnership to characterize the hydrogeologic setting of the Chehalis River basin study area (fig. 1) and to develop a better understanding of the interaction of groundwater and surface-water in selected representative areas. Accurate well location and identification of respective logs were essential in the characterization of the hydrogeologic setting. The measurement of groundwater levels is an important component to develop a better understanding of the groundwater flow system in the study area.

Purpose and Scope

This report presents groundwater levels and associated well information from a USGS field inventory of 360 wells in the Chehalis River basin study area. During the field inventory (July 2009–September 2009) all groundwater-level measurements were made by personnel from the USGS Washington Water Science Center using standard techniques described in Drost (2005). These data and additional information about well construction are stored in the USGS National Water Information System (NWIS), Groundwater Site Inventory (GWSI) database. The groundwater level data collected during the field inventory document the spatial distribution of water levels in the study area during late summer 2009. These data will be used along with the lithologic information from drillers’ logs to develop a better understanding of the groundwater flow system in the area. Eighteen of the sites inventoried will be monitored monthly (October 2009 through October 2010) to document changes in water levels and to characterize the interaction of groundwater and surface water in representative parts of the study area.

Well-Numbering System

Wells in the study area were assigned a unique well local number that locates and identifies each well in the Public Land Survey rectangular grid system for Washington State (fig. 2). For example, given the well number 20N/06W-28C02D1, the number and letter preceding the slash (20N) indicate the township north of the Willamette Base Line. The number and letter between the slash and the hyphen (06W) indicate the range west of the Willamette Meridian. The number following the hyphen (28) indicates the section number in the township. Most townships in the study area are divided into 36-mi² sections; however, Washington Territory Donation Land Claims of 1852–55 predate the Public Land Survey and are not regular 1-mi² sections. These early Donation Land Claims are depicted on maps as irregular-sized and shaped sections and are assigned section numbers greater than 36. The letter following the section number (C) indicates the 40-acre quarter-quarter tract in the section. The number following the quarter-quarter (02) is the sequence number used to distinguish individual wells in the same quarter-quarter tract. A “D” following the sequence number indicates a well that has been deepened. A “P” following the sequence number indicates a piezometer.

Well Locations and Water Levels

Well locations are plotted on an interactive image of the study area located at http://wa.water.usgs.gov/projects/chehalis/sites.htm. The map image can be manipulated using the buttons in the upper-left corner of the image or by clicking with the mouse to pan and double-clicking to zoom. Holding the cursor over a plotted well site opens a message box that displays the local well number. A listing of all wells shown on the map is presented in table 1. Clicking on the well location on the interactive map will provide another dialog box with information about the well location, elevation, depth, and water level when available. A link to the NWIS is also presented to provide additional information about the site.

Acknowledgments

The authors thank the many individual well owners, local businesses, and local, tribal, and state governments for their cooperation in providing access to the wells used for this study.

Reference Cited

Drost, B.W., 2005, Quality-assurance plan for groundwater activities: U.S. Geological Survey Open-File Report 2005-1126, 33 p.

First posted June 23, 2010