Edwards Aquifer, water quality, and politics

In response to recent news of the pro-development, anti-local-water-quality-regulation bills proposed in the Texas legislature by Senator Armbrister (not to mention Senator Madla's separate pro-development, anti-other-local-regulation bills), Cincinnatus asks for background information on the issue of development over the Edwards aquifer, the sole current water supply for most of San Antonio.  I do have some knowledge of this, so I was inspired to do some more reading.  Here goes my attempt to help out.

First, a list of expert resources on the Web:

• Edwards Aquifer Authority:  created by the Texas leglislature in the mid-1990s as a response to federal court decisions; charged with preserving and protecting the aquifer;
• Greater Edwards Aquifer Alliance: a recently-formed alliance of environmental groups dedicated to protecting the aquifer;
• Gregg Eckhardt's Edwards Aquifer Homepage:  the ultimate resource for Edwards aquifer information of all sorts.

Now, my attempt at an overview.  Examine a map of Texas aquifers. The Edwards recharge zone, where water on the surface flows underground to enter the aquifer, is the thin blue area in south central Texas.  On the map, it looks inconsequential next to the Trinity (green) and Carrizo-Wilcox (red) aquifers.  So why is the Edwards so important?

The essential reason for the importance of the Edwards aquifer is simple:  a large amount of high quality water is cheaply available to a large city and many smaller towns.  While the other aquifers in central Texas recharge very slowly and so are very vulnerable to over-pumping, the Edwards aquifer recharges very quickly after substantial rains.  Much more water can thus be taken from it without depleting it. A local expert, Gregg Eckhardt, calls the Edwards "one of the most prolific artesian aquifers in the world."  (Alas, the aquifer's high recharge is not quite enough to meet current water needs and obligations, much less future ones, especially given the unreliability of rains in this part of Texas.  So there are a lot of contentious issues surrounding who can use how much water and when.  Such issues are beyond the scope of this post, but Eckhardt's website is a great place to learn about them.)

This speedy recharge is due to the extreme porosity of the Edwards limestone, the rock that contains the Edwards aquifer.  This rock is ridden with large holes and tunnels through which water can flow relatively unimpeded.  Substantial creeks that flow over the recharge zone (where the Edwards limestone is at the surface) frequently end up completely in the aquifer. Eckhardt writes:

It is not uncommon for the Cibolo to flow 30 feet wide and a foot deep and, in the space of a quarter mile, disappear completely into the Edwards formation.

This suggests why allowing unregulated development along the recharge zone and in areas upstream of the recharge zone could be a serious problem:  pollutants ("from fertilizers and pesticides to toxic metals and sewage spills") have a very easy path from the surface straight into the heart of the aquifer. Since the early 1990s, as San Antonio's sprawl has reached the recharge zone, this issue has exploded into prominence, pitting the interests of the developers against those of the bulk of the community in San Antonio and other towns that rely on Edwards aquifer water.

The Greater Edwards Aquifer Alliance provides some more detail on the dangers:

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.

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.

The current water quality of Edwards aquifer water in the San Antonio area is very good, but, according to Gregg Eckhardt, there are signs from other sections of the aquifer that this may not always be the case:

The Edwards Aquifer Authority conducts an extensive testing program in which many wells are routinely analyzed for pesticides, herbicides, and almost every chemical that people use or produce.  In 2000, the concentration of every pesticide, herbicide, and VOC [volatile organic compounds] tested for was below the detection limits of the test used.  The same cannot be said for Barton Springs in Austin, which occur in Edwards limestones that are hydrogeologically separated from the much larger and more prolific San Antonio section.  At Barton Springs, scientists with the United States Geological Survey have been sampling for pesticides since 2000 and have regularly detected a few pesticides at low concentrations during baseflow conditions, and a larger suite at much higher concentrations just after rain events.  Many regard the water quality problems at Barton Springs as a warning to other regional users of what will happen if Edwards recharge quality is not adequately protected.

Eckhardt adds that allowing the aquifer to become polluted would be very expensive:

Once water in the Aquifer becomes contaminated, it will be very difficult and perhaps impossible to clean.  The only alternative might be to treat water by conventional means after it is pumped to the surface, an expensive proposition that most cities other than San Antonio have already had to invest in.  In most cities, water is drawn from a river or reservoir, treated in a central location, and sent to customers over a wide area through very large distribution mains.  In San Antonio, there are many Edwards wells all over the city where water is pumped out, stored in tanks, and distributed to the local area.  There are no large conveyance systems and there would be no way to move large amounts of water from a central treatment facility if it became necessary.  Instead, there would probably have to be a large number of smaller treatment facilities, which are more expensive to build and operate.  If it became necessary, the cost for treating Edwards water would be a very big number indeed.  Whatever that number is, that is the value of the treatment the Aquifer is currently providing for free.

In 1995, San Antonio enacted the first rules and guidelines for development over the recharge zone.  But only 2% of the zone is within San Antonio's jurisdiction, so more widespread requirements for ecologically sound development are needed. 

The Edwards Aquifer Authority, run by an elected board, and which encompasses all or parts of eight central Texas counties, has been slowly moving towards establishing such rules over the last few years—in particular, placing a limit on the amount of impervious cover.  It appears that one of Sen. Armbrister's recent bills is a direct response to this rule-making process—an attempt to shut it down before it gets any further. I hope to have a chance to write more about that soon.

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