Despite the immeasureable value of this natural resource, human activity - urbanization - now threatens to taint the water of the Edwards Aquifer with a slew of pollutants - from fertilizers and pesticides to toxic metals and sewage spills.

The Edwards Aquifer and its Great Springs are highly vulnerable because of their unique geology and hydrology. Caves, sinkholes, faults, and fractures dot the landscape of the Recharge Zone, where water plunges underground, where it encounters limestone rock that as been eroded over time to create large underground channels for the water to flow.

Water in the Edwards Aquifer moves at a rate of thousands of feet per day; compared to velocities of a few feet per year in other aquifers. This rapid movement and the relatively large size of the spring outlets provide none of the filtration, absorption, and slow water flow that protect many aquifers from contamination.

Development in the Recharge Zone and upstream of the Recharge Zone in the Contributing Zone of new subdivisions, shopping centers, office buildings, highways, golf courses, sewer lines, wastewater treatment plants, and rock quarries all create increased risk of contamination of the aquifer.

We are literally poisoning our drinking water when we allow development to take place that will undeniably increase loads of pollutants over the sensitive karst limestone aquifer.

Urban development creates numerous sources of water pollution. First, the construction phase transforms farm, ranch, forest, and pasture land into large areas of disturbed soil. Central Texas' erratic weather patterns can dump 6-10 inches of rainfall in a short time span. Erosion and sedimentation controls at construction sites are often overwhelmed by heavy rains and the result is muddy run-off leaving the site and entering a creek and eventually the aquifer and springs.

Large scale construction activity leads to increased sediment loads that wash off of construction sites.
At right, silt fences are not capturing sediment-laden runoff at a highway construction site.

When construction is completed, the development transforms pervious land into impervious cover, which means any surface that water cannot pass through, such as roofs, parking lots, and roads. These surfaces prevent rainfall from being filtered through vegetation and absorbed by soil, thereby increasing the percentage of rainfall that becomes storm water. Rainfall that hits pavement washes oil, grease, and other urban contaminants off their surfaces and into creeks, streams and recharge features. Increased impervious cover also leads to increased flooding and erosion of stream banks, which results in higher levels of sediments entering the aquifer and emerging at the Springs.

New developments typically are required to install "water quality controls" or "best management practices," engineered structures designed to capture the "first flush" of stormwater runoff, which has a higher percentage of pollutants. The "first flush" is routed into a pond or filter that removes some pollutants. However, no structured control achieves 100% removal of pollutants. Click here to read a U.S. Geological Survey report on performance of structured controls. In some instances, the structured controls accumulate pollutants that are then washed out of the control by a very heavy rain event. The bottom line is that history has proven engineered controls cannot and do not prevent pollution of water in the Edwards Aquifer watershed.

Increased urbanization of the Edwards Aquifer has led to increased numbers of vehicles traveling over the aquifer. In turn, this has led to increased contaminants from automobiles, such as polycyclic aromatic hydrocarbons (or PAHs), entering the aquifer. Most roadways over the aquifer do not have "water quality controls" to capture these contaminants that are continually emitted by vehicles.

Increased numbers of residential subdivisions over the aquifer has led to increases in fertilizers, pesticides, fungicides, and other house hold chemicals that wash off of lawns and end up in the aquifer and springs. Golf courses are also a leading source of these contaminants, as Hill Country soils are not capable of supporting golf turf without massive chemical applications to provide nutrients and fend off insects and fungi.

Increased and concentrated residential development also creates miles of sewer pipes, which can crack and leak without being detected, sometimes dumping raw sewage into fractures and fissures. Sewage lift stations can fail, and sewer manholes can overflow.

We advocate for prevention of pollution of the Edwards Aquifer by preventing the type of developments that threaten our water and endangered species. In fact, it would be cheaper to protect the Edwards Aquifer through conservation easements and parklands purchases than it would cost taxpayers to build the roads, schools, water and wastewater systems for development that threatens our water.

In sum, the Edwards Aquifer watershed is too vulnerable to accommodate the influx of new residents that business boosters and developers would like to see.