Hydrology and quality of ground water in northern Thurston County, Washington

Water-Resources Investigations Report 92-4109
By: , and 

Links

Abstract

Northern Thurston County is underlain by as much as 1,800 feet of unconsolidated deposits of Pleistocene Age that are of glacial and nonglacial origin. Iterpretation of approximately 1,140 drillers' logs led to the delineation of seven major geohydrologic units, four of which are significant aquifers.

Precipitation ranges from about 35 to 65 inches per year across the study area. Estimates of recharge indicate that the ground-water system of the Ground Water Management Area (GWMA), a subset of the study area, receives an average of about 28 inches per year. Ground water generally moves toward marine water bodies and to major surface drainage channels.

At least 33,000 acre-feet per year of ground water discharges as springs from the GWMA. Approximately 21,000 acre-feet of water was withdrawn from the ground-water system of the GWMA through wells in 1988. Total ground-water use in the GWMA in 1988 was approximately 37,000 acre-feet. About 16,000 acre-feet of water that discharges naturally through springs was used together with water withdrawn by wells for domestic supply, agricultural, commercial, industrial, institutional, and aquaculture and livestock uses.

Generally, the chemical quality of the ground water was good and 94 percent of the water samples were classified as soft or moderately hard. Of the few water-quality problems encountered, the most widespread anthropogenic problem appeared to be seawater intrusion. However, a comparison with data from 1978 indicated that the degree and extent of intrusion had not changed significantly since that time. Agricultural activities may be responsible for the presence of nitrate in ground waters at some individual wells, but septic tanks in areas of high housing density are likely responsible for elevated nitrate concentrations near the Cities of Lacey and Tumwater. The close correlation of nitrate concentrations with detergent concentrations supports the theory that the nitrate originates in septic systems, the only likely source of the detergents.

Most water-quality problems in the study area, however, are due to natural causes. Iron concentrations are as large as 21,000 micrograms per liter, manganese concentrations are as large as 3,400 micrograms per liter, and connate seawater is present in ground water in the southern part of the study area.

Study Area

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Hydrology and quality of ground water in northern Thurston County, Washington
Series title Water-Resources Investigations Report
Series number 92-4109
DOI 10.3133/wri924109
Year Published 1998
Language English
Publisher U.S. Geological Survey
Description Report: v, 230 p.; 6 Plates: 36.00 x 40.00 inches or smaller
Country United States
State Washington
County Thurston County
Google Analytic Metrics Metrics page