In 1996 northwestern Pierce County, Washington, consumed
22 billion gallons of water, 15 billion gallons of it being imported from
surface-water sources outside the area
bytes). The people of this 88-square-mile area near Puget Sound, where
the population is growing vigorously and the land is being rapidly developed,
have reached the limits of their surface-water supply and are turning to
its ground water.
But what is the
nature of the little-understood ground-water system that people are coming
to depend on? How much water can it supply? What is the quality of the
water? How will greater demands for the ground water affect nearby wells,
springs, lakes, and wetlands? A new report from the U.S. Geological Survey
presents a portrait of the ground-water system under Tacoma and Puyallup
that will point the way to answers.
system we've described will help state and local water managers know what
to expect of the aquifers--how much water they can produce and where the
better supplies are," explained M.A. Jones, the lead USGS investigator
of the project.
The new report
presents the results of a half-million-dollar investigation begun in 1995
by the USGS in cooperation with the Tacoma-Pierce
County Health Department, the
Department of Ecology, and the Cities of Puyallup
worked from 255 drillers' logs, published maps of the surficial geology,
and cross sections of the area's thick deposits of unconsolidated material
laid down during the Quaternary Period, from 1.6 million years ago to the
present. The USGS delineated a layer-cake local system of five coarse-grained
aquifers alternating with five fine-grained semiconfining units and underlain
by deep undifferentiated deposits (figure, 42589 bytes).
Ground water in the two most important aquifers, dubbed Qc1 and Qc2, generally
moves east and northeast into the Puyallup River and north to Commencement
Bay, and Puget Sound.
Of the 6,890 million
gallons of ground water withdrawn from the area in 1996 for all uses, aquifers
Qc1 and Qc2 supplied by far the most--2,790 and 2,320 million gallons (table,
14198 bytes). A ground-water budget constructed for the shallow units,
aquifer Qc1 and above, revealed that 86 percent of the quantified recharge
in the system discharges through these shallow units. The USGS concluded
that these shallow units make up the local ground water system and that
aquifer Qc2 and the units below are more properly a part of a regional
found that the quality of the ground water in the 33 wells and springs
they sampled was generally good (figure, 61466 bytes).
In only one well did the concentration of the pesticide dieldrin in the
water exceed drinking-water standards for human health, and in water from
only four wells or springs did total coliform exceed drinking-water health
standards. In eight wells or springs, water contained iron or manganese
concentrations above secondary drinking-water standards, which are chiefly
aesthetic, not health-related standards. The samples from all 33 wells
and springs were analyzed for nitrite-plus-nitrate, major ions, arsenic,
iron, manganese, bacteria, and checked for pH, temperature, specific conductance,
alkalinity, and dissolved oxygen (table, 19114 bytes)
and (figure, 43591 bytes). Only some samples were
analyzed for trace elements, methylene blue active substances, boron, radon,
pesticides, total organic carbon, and volatile organic compounds.
The report, Ground-Water
Hydrology of the Tacoma-Puyallup Area, Pierce County, Washington, by M.A.
Jones, L.A. Orr, J.C. Ebbert, and S.S. Sumioka, is published as U.S. Geological
Survey Water-Resources Investigations Report 99-4013. The report is available
for reading at the U.S. Geological Survey, WRD, 934 Broadway, Suite
300, Tacoma, Washington 98402, telephone (253) 552-1600. (abstract,
3191 bytes) and (table of contents, 27846
As the nation's
largest water, earth, and biological science and civilian mapping agency,
the USGS works in cooperation with more than 2,000 organizations across
the country to provide reliable, impartial, scientific information to resource
managers, planners, and other customers. This information is gathered in
every state by USGS scientists to minimize the loss of life and property
from natural disasters, contribute to sound economic and physical development
of the nation's natural resources, and enhance the quality of life by monitoring
water, biological, energy, and mineral resources.
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