Vertical temperature and chemical gradients in groundwater in the Tucson Basin, Arizona
Abstract
A study of vertical temperature and chemical gradients in groundwater
was conducted, primarily to determine whether or not temperature
gradients could be used as an index of vertical mixing in well bores and,
hence, as a guide in the interpretation of point samples taken at various
depths for chemical analysis. Measurements of temperature variation with
depth in well bores were made with a pre-calibrated thermistor. Water
samples were taken with point samplers at specific depths.
Graphical comparisons of profiles of temperature, electrical conductivity,
and bicarbonate and chloride contents indicate agreement with
the assumed hypotheses of vertical flow and/or mixing in well bores for
50% of the wells sampled. Anomalies were found in the chemical gradients.
Incomplete chemical analysis was noted as an important factor of the
chemical anomalies. The water chemistry was relatively uniform and the
variation with depth was not pronounced. pH studies indicated that the
water is in, or close to, equilibrium with respect to calcite in most of
the wells. The water is predominantly of iodium or calcium bicarbonate
type in irrigation water class C2-SI.
It was preliminarily concluded that vertical temperature gradients
can be us ed as a guide in the interpretation of the chemistry of samples
taken at various depths in a well bore.