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The depth to the water table can change (rise or fall)
depending on the time of year. During the late winter and
spring when accumulated snow starts to melt and spring
rainfall is plentiful, water on the surface of the earth
infiltrates into the ground and the water table rises. When
water-loving plants start to grow again in the spring and
precipitation gives way to hot, dry summers, the water table
will fall because of evapotranspiration. The most reliable
method of obtaining the depth to the water table at any
given time is to measure the water level in a shallow well
with a tape. If no wells are available, surface geophysical
methods can sometimes be used, depending on surface
accessibility for placing electric or acoustic probes. Data
bases containing depth-to-water measurements made in the
past are maintained by the USGS. Your state government
probably maintains a data base of drillers' logs that have
water-levels recorded when a well was drilled, and
hydrologic consultants often have reports that contain
water-level data from shallow boreholes. Consulting any or
all of these sources is a good first step in finding out the
depth to the water table. |