A study was conducted to determine the relative influence of
mountain-front infiltration in the Ryan Flat subbasin and to
determine whether recent recharge (post-1940), which is of
importance to water-use planning, has reached the Salt Basin
aquifer, Trans-Pecos Texas. The alluvial and volcanic Salt Basin
aquifer lies within a bolson, and the average depth to water in
most of the subbasin is approximately 250 feet. Concentrations of
the chlorofluorocarbons CFC-11, CFC-12, and CFC-113, as well as
tritium, were measured in water from 10 wells in the study area.
CFC-model recharge dates ranged from pre-1940 to the early
1970's. Ground water in five wells had CFC-model dates of pre-1940
or pre-1945. Ground water in two wells had dates of the mid- to
late 1940's. Ground water from one well had a CFC-model recharge
age of the early 1950's. Samples from the remaining two wells were
most probably contaminated in some manner and are probably
unreliable. CFC-model ages were calculated independently for the
three chlorofluorocarbons, though the presence of volatile
organic compounds affected agreement among them. Tritium
activities in the nine wells for which tritium was analyzed
indicated pre-1953 recharge and thus agreed approximately with
the CFC-model dates.
Ground water was analyzed for selected water-quality
constituents. Water from all wells met U.S. Environmental
Protection Agency national primary and secondary drinking water
standards for all tested constituents except fluoride in samples
from three wells. Silica concentrations in water from six wells
exceeded a range considered typical in natural waters.
