Geology topics

Research about Thurston County, Washington

Source-linked reports with geographic coverage including Thurston County, Washington.

3 recordsLinked to original sources

USGS2013

Effect of simulated tree canopy removal on a municipal wellfield in the Puget Sound aquifer system, Thurston County, Washington

Effects of tree canopy removal on a wellfield were simulated using a groundwater flow model characteristic of hydrogeologic settings in the Puget Sound aquifer system. Effects were estimated according to simulated changes in flow patterns that may result from tree canopy removal associated with varying degrees of residential development. The flow model used was a modified version of a model of the hydrogeologic setting in Thurston County, Washington; the wellfield was one planned for Olympia, Washington, and the canopy modifications spanned a range of possible land use change scenarios. The relative effects of tree canopy removal were estimated in terms of potential changes in capture zones for the wellfield and groundwater levels. Because of the depth of the wellfield and the dispersal of the effects from changes in recharge at ground surface, potential changes in wellfield capture zones and groundwater levels were discernible but small compared to other possible influences.

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USGS1998

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

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 Approximately 21,000 acre-feet of water was withdrawn from the ground-water system of the GWMA through wells in 1988.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.

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USGS1994

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

Northern Thurston County is underlain by as much as 1,000 feet of unconsolidated deposits of Pleistocene Age, that are of both glacial and nonglacial origin. Interpretation of 17 geologic sections led to the delineation of 7 major geohydrologic units, 3 of which constitute aquifers in the area. Precipitation ranges from about 35 to 65 inches per year across the study area. Estimates of gross recharge from precipitation indicate that the ground-water system of the area receives about 25 inches per year. The net recharge to the system (recharge from precipitation minus withdrawals from wells) is the equivalent of about 23 inches per year. Ground water generally moves toward marine bodies and to major surface drainage channels. Leakage from Lake St. Clair, which lies in a compound kettle within permeable glacial outwash, is almost 24 feet per year per unit area. Leakage from the lake may make up part of the water that discharges at McAllister Springs, north of the lake. Of the few water-quality problems encountered, the most widespread is seawater intrusion, which is caused by the activities of man. 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 pan of the study area.

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