The Edwards Aquifer is 180 miles long extending from Brackettville, TX to
Kyle, TX and varies in width from 5 to 40 miles. The Edwards consists of an
unconfined portion where recharge occurs, and a deeper (800-1200 feet)
confined or artesian portion through which groundwater flows in the east,
northeast direction toward the cities of San Antonio, New Braunfels, and San
Marcos. The lower boundary is the underlying Glen Rose Formation. A "badwater"
line defines the southern limits of the aquifer, where saline water with TDS
greater than 1,000 mg/l occurs. The Edwards is the primary source of drinking
water for more than 1.5 million people in and near San Antonio. The aquifer
is also vital to the agricultural and light industrial economy of the region.
This karstic aquifer consists of several layers of dense carbonate rocks that
have been dolomitized, chertified, and calcitized. The Edwards Aquifer is a
prolific aquifer because of its great thickness and areal extent, high
infiltration capacity in the recharge zone, and historically high water quality.
Various creeks and rivers passing over transmissive outcrops form the recharge
zone, where faults and connected fractures facilitate the infiltration of
water through the karstified formation.
The highly transmissive nature of the Edwards Aquifer recharge zone allows
for rapid recharge, a benefit in terms of water quantity, but may make the
aquifer highly vulnerable to contamination if the resource is not probably
understood or managed. The Edwards Aquifer Authority regulates growth and
development in the recharge zone to maintain the water quality in the Edwards.
With increasing urban and agricultural activities and higher pumping rates,
the water quality of the aquifer may be degraded. It thus becomes important to
monitor the levels of various organic and inorganic compounds entering the
aquifer, through runoff and other sources so as to control the water quality.
VOC contamination of ground water in the recharge zone of the Edwards seems to
be limited to localized areas in the city of San Antonio and Uvalde County.
San Antonio is located primarily on strata that confine the Edwards aquifer,
but residential and commercial development has expanded to the outcrop of the
Edwards aquifer where some VOCs have been detected. In Uvalde County some
development also has occurred on the Edwards aquifer outcrop. Because of
continuing development in the highly vulnerable areas of the Edwards Aquifer
recharge zone there is a need to better characterize existing contamination
and the source of contamination, as well as studying factors controlling
contaminant transport in this complex aquifer system.
The purposes of my research are to: map existing ground-water contamination
using GIS, and identify sources of contamination using stable isotope analysis
of ground-water samples. This work will lead to a greater understanding of
contaminant fate and transport in the Edwards Aquifer.
